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Рудный потенциал щелочного, кимберлитового и карбонатитового магматизма

Журнальные статьи

Aragon, Eugenio; D'Eramo, Fernando; Castro, Antonio; et al.Tectono-magmatic response to major convergence changes in the North Patagonian suprasubduction system; the Paleogene subduction-transcurrent plate margin transition//TECTONOPHYSICS Volume: 509 Issue: 3-4 Pages: 218-237 Published: AUG 15 2011

The southern and central Andes reflect significant along-strike differences of tectonic activity, including shortening, alternating flat-to-normal subduction styles and magmatism. In northern Patagonia, the subduction/supra-subduction system, fore arc, arc and back arc basins developed in an extensional setting during the Paleogene. This was accompanied by landward migration of calc-alkalic magmatism which changed to synextensional bimodal volcanism of rhyolitic ignimbrites and interbedded tholeiitic and alkalic basalts. These Paleogene events occurred during a time when the Farallon-Aluk active ridge reached the South American plate, and the Farallon plate subduction was interrupted. They represent a new tectonic regime, characterized by a transcurrent plate margin. The presence in the back arc of a rigid lithospheric block of 100,000 km(2) represented by the North Patagonian Massif focused the rotation of the coastal blocks. This resulted in the development of two Paleogene extensional regions to the north and south, respectively, of the Massif and replaced the former back arc. Plate rearrangement caused by the inauguration of the Nazca plate and its regime of orthogonal subduction at the beginning of the Miocene, re-established typical calc-alkaline arc magmatism at the former upper Cretaceous arc locus. Present seismic activity in the subducted plate and tomographic modeling of p-wave velocity anomalies in the upper mantle also suggest the presence of a subduction gap that lasted for most of the Paleogene in northern Patagonia. (C) 2011 Elsevier B.V. All rights reserved.

Arai, Shoji; Ishimaru, Satoko Zincian chromite inclusions in diamonds: Possibility of deep recycling origin//JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES Volume: 106 Issue: 2 Pages: 85-90 Published: APR 2011

It was reported by Meyer and Boyd (1972) that zincian chromite, having 2 wt% to 3 wt% ZnO and high (>0.9) Cr# (= Cr/(Cr + Al) atomic ratio), appears as inclusions in diamonds obtained from kimberlite. Zincian chromite is characterized by a low (<0.03) Mg# [= Mg/(Mg + ferrous Fe + Zn + Mn + Ni + Co) atomic ratio] and an appreciable amount of MnO (0.4-0.5 wt%). The chemistry of zincian chromite is very different from commonly found chromite inclusions (magnesiochromite) in diamonds, which contain low amounts of ZnO (<0.1 wt%) and MnO (<0.1 wt%). Zincian and manganoan chromites are also commonly found in meteorites and in altered/metamorphosed peridotites and related rocks. The chromites found in meteorites mostly have an intermediate Mg# (0.2-0.5) and a high Cr# (mostly >0.8); moreover, the major-element chemistry of these chromites is similar to that of the magnesiochromite inclusions in diamonds. Spinels obtained from altered rocks show a chemical range that comprises the zincian chromite inclusions found in diamonds. The origin of these inclusions possibly lies in deep recycling. They were initially formed at the Earth's surface in altered/metamorphosed peridotites; they then sank deep down into the mantle and were entrained to the surface again by kimberlite magmatism.

Arslan, Mehmet; Temizel, Irfan; Abdioglu, Emel; et al.Ar-40-Ar-39 dating, whole-rock and Sr-Nd-Pb isotope geochemistry of post-collisional Eocene volcanic rocks in the southern part of the Eastern Pontides (NE Turkey): implications for magma evolution in extension-induced origin //CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 166 Issue: 1 Pages: 113-142 Published: JUL 2013

The Eocene volcano-sedimentary units in the southern part of the Eastern Pontides (NE Turkey) are confined within a narrow zone of east-west trending, semi-isolated basins in Bayburt, GumuAYhane, Airan and Alucra areas. The volcanic rocks in these areas are mainly basalt and andesite through dacite, with a dominant calc-alkaline to rare tholeiitic tendency. Ar-40-Ar-39 dating of these volcanic rocks places them between 37.7 +/- A 0.2 and 44.5 +/- A 0.2 Ma (Middle Eocene). Differences in the major and trace element variations can be explained by the fractionation of clinopyroxene +/- A magnetite in basaltic rocks and that of hornblende + plagioclase +/- A magnetite +/- A apatite in andesitic rocks. Primitive mantle-normalized multi-element variations exhibit enrichment of large-ion lithophile elements and to a lesser extent, of light rare earth elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magma derived from an enriched mantle source. Chondrite-normalized rare earth element patterns of the aforementioned volcanic rocks resemble each other and are spoon-shaped with low-to-medium enrichment (La-N/Lu-N = 2-14), indicating similar spinel lherzolitic mantle source(s). Sr, Nd and Pb isotopic systematics imply that the volcanic rocks are derived from a subduction-modified subcontinental lithospheric mantle. Furthermore, post-collisional thickened continental crust, lithospheric delamination and a subduction-imposed thermal structure are very important in generating Tertiary magma(s). The predominantly calc-alkaline nature of Eocene volcanic rocks is associated with increasing geodynamic regime-extension, whereas tholeiitic volcanism results from local variations in the stress regime of the ongoing extension and the thermal structure, as well as the thickness of the crust and the mantle-crust source regions. Based on volcanic variety and distribution, as well as on petrological data, Tertiary magmatic activity in Eastern Pontides is closely related to post-collisional thinning of the young lithosphere, which, in turn, is caused by extension and lithospheric delamination after collisional events between the Tauride-Anatolide Platform and the Eurasian Plate.

Bachmann, Olivier; Deering, Chad D.; Ruprecht, Janina S.; et al. Evolution of silicic magmas in the Kos-Nisyros volcanic center, Greece: a petrological cycle associated with caldera collapse//CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 163 Issue: 1 Pages: 151-166 Published: JAN 2012

Multiple eruptions of silicic magma (dacite and rhyolites) occurred over the last similar to 3 My in the Kos-Nisyros volcanic center (eastern Aegean sea). During this period, magmas have changed from hornblende-biotite-rich units with low eruption temperatures (<= 750-800 degrees C; Kefalos and Kos dacites and rhyolites) to hotter, pyroxene-bearing units (>800-850 degrees C; Nisyros rhyodacites) and are transitioning back to cooler magmas (Yali rhyolites). New whole-rock compositions, mineral chemistry, and zircon Hf isotopes show that these three types of silicic magmas followed the same differentiation trend: they all evolved by crystal fractionation and minor crustal assimilation (AFC) from parents with intermediate compositions characterized by high Sr/Y and low Nb content, following a wet, high oxygen fugacity liquid line of descent typical of subduction zones. As the transition between the Kos-Kefalos and Nisyros-type magmas occurred immediately and abruptly after the major caldera collapse in the area (the 161 ka Kos Plateau Tuff; KPT), we suggest that the efficient emptying of the magma chamber during the KPT drew out most of the eruptible, volatile-charged magma and partly solidified the unerupted mush zone in the upper crust due to rapid unloading, decompression, and coincident crystallization. Subsequently, the system reestablished a shallow silicic production zone from more mafic parents, recharged from the mid to lower crust. The first silicic eruptions evolving from these parents after the caldera collapse (Nisyros units) were hotter (up to >100 degrees C) than the caldera-forming event and erupted from reservoirs characterized by different mineral proportions (more plagioclase and less amphibole). We interpret such a change as a reflection of slightly drier conditions in the magmatic column after the caldera collapse due to the decompression event. With time, the upper crustal intermediate mush progressively transitioned into the cold-wet state that prevailed during the Kefalos-Kos stage. The recent eruptions of the high-SiO(2) rhyolite on Yali Island, which are low temperature and hydrous phases (sanidine, quartz, biotite), suggest that another large, potentially explosive magma chamber is presently building under the Kos-Nisyros volcanic center.

Bindeman, I. N.; Serebryakov, N. S.Geology, Petrology and O and H isotope geochemistry of remarkably O-18 depleted Paleoproterozoic rocks of the Belomorian Belt, Karelia, Russia, attributed to global glaciation 2.4 Ga //EARTH AND PLANETARY SCIENCE LETTERS Volume: 306 Issue: 3-4 Pages: 163-174 Published: JUN 15 2011

This paper deals with strongly O-18-depleted (down to -27.3 parts per thousand VSMOW) 1.9Ga Paleoproterozoic mid-grade metamorphic rocks found in the Belomorian Belt of Karelia (E. Baltic Shield). The protolith of these rocks is attributed to have been altered by glacial meltwaters during the world's first 2.4-2.3 Ga Paleoproterozoic "Slushball" glaciation, when Karelia was located near equatorial latitudes. We describe in detail three and report seven new localities with unusually depleted O-18 signatures that now span 220 km across the Belomorian Belt. Hydrogen isotope ratios measured in amphibole, biotite and staurolite also display remarkably low values of -212 to -235 parts per thousand. Isotope mapping in the three best exposed localities has allowed us to identify the world's most O-18 depleted rock, located at Khitostrov with a delta O-18 value 27 parts per thousand. In Khitostrov samples, zircons have normal delta O-18 detrital cores and low-delta O-18 metamorphic rims. Mapping demonstrates that zones of delta O-18 depletion occur in a concentric pattern 100-400 m in dimension, and each locality displays significant delta O-18 and ED heterogeneity on a meter to centimeter scale, characteristic of meteoric-hydrothermal systems worldwide. The zone of maximum delta O-18 depletions usually has the highest concentration of metamorphic corundum, rutile, and zircon and also display doubled concentrations of insoluble trace elements (Zr, Ti, Cr, HREE). These results are explained by elemental enrichment upon mass loss during hydrothermal dissolution in pH-neutral meteoric fluid. Remarkably low-delta O-18 and ED values suggest that alteration could have only happened by glacial meltwaters in a subglacial rift zone. Many localities with delta O-18 depletions occur inside metamorphozed 2.4 Ga gabbro-noritic intrusions, or near their contact with Belomorian gneisses, implying that the intrusions were driving meteoric hydrothermal systems during the known 2.4 Ga episode of Belomorian rifting. Given that the isotopically-depleted localities now spread over 200 km, the extent of the Karelian ice cap is estimated to be at least that large. Svecofennian 1.9 Ga metamorphism is seen to cause metamorphic recrystallization of hydrothermally-altered rocks into coarse-grained assemblages, and causing local metasomatism through devolatilization of the underlying hydrous low-delta O-18 protolith, further depleting ED via volatilization. This process led to gem-quality rubies and kyanites that preserve these remarkable delta O-18 values in the geologic record. (C) 2011 Elsevier B.V. All rights reserved.

Caffe, Pablo J.; Trumbull, Robert B.; Siebel, Wolfgang Petrology of the Coyaguayma ignimbrite, northern Puna of Argentina: Origin and evolution of a peraluminous high-SiO2 rhyolite magma//LITHOS Volume: 134 Pages: 179-200 Published: MAR 2012

The Coyaguayma ignimbrite is a strongly peraluminous (SP), sillimanite, garnet-bearing silicic rhyolite which erupted in the northern Puna segment of the central Andean plateau in the Upper Miocene (similar to 11 Ma), a period that was characterized by the eruption of voluminous (100s to 1000s km(3)) dacitic ignimbrites of high-K calc-alkaline affinity. In this region, the SP magmatic rocks are both rare and small, but their importance is potentially much greater as rocks of this type are usually interpreted as products of crustal melting and therefore useful for addressing mantle addition vs crustal recycling in the central Andes. The phenocryst assemblage of the Coyaguayma ignimbrite comprises plagioclase (An26-18), quartz, Ba-rich and Ba-poor sanidine, minor Al-rich ferromagnesian minerals (AI(T)- and Al-VI-rich biotite, almandine-spessartine garnet) and sillimanite, as well as accessory zircon and monazite. Textural relations suggest that the accessory and ferromagnesian phases crystallized before quartz and feldspars. Mineral equilibria suggest that crystallization of the rhyolite magma began at similar to 5 kbar and 800 degrees C, and continued almost isobarically to 720 degrees C, causing the residual liquid to increase H2O contents from similar to 4-5% to similar to 7.5% before eruption. Most major features (e.g., high SiO2, A/CNK > 1.3, low Ca, MgO, TiO2 and FeO) and trace element patterns (low Ba, Sr, Th, LREE and Eu/Eu*.; high Rb, U, Y and Nb), along with the thermobarometric constraints on magmatic P. T and water contents are consistent with an origin by mica dehydration melting of metapelitic sources (e.g., typical biotite-muscovite gneisses from the outcropping S Puna basement). However, the relatively low initial Sr-87/Sr-86 (similar to 0.7125), and high Nd-143/Nd-144 (similar to 0.512200) ratios invalidate a pure crustal origin. Instead, we propose contamination of calc-alkaline dacitic magmas similar to typical Puna ignimbrites by metapelite at mid-crustal settings (>= 18 km depth). Geochemical modeling that satisfies the chemical and isotopic data suggests mixing of 70% dacite and similar to 30% of metapelite partial melts, followed by extensive (70%) fractionation of plagioclase, K-feldspar, quartz and biotite, with minor magnetite and apatite from the hybrid magma. Sillimanite in the Coyaguayma rhyolite is interpreted as a restite mineral or a product of incongruent melting of the metapelite, which was preserved intact in the hybrid melt due to local equilibrium. This petrogenetic model explains most characteristics of crystal-poor SP rhyolites from the Puna plateau (e.g., Tocomar, Ramadas rhyolites) and it may be more generally applicable to occurrences of SP magmas in Andean-type continental arcs dominated by calc-alkaline magmatism. (C) 2011 Elsevier B.V. All rights reserved.

Chauvet, Francois; Lapierre, Henriette; Maury, Rene C.; et al. Triassic alkaline magmatism of the Hawasina Nappes: Post-breakup melting of the Oman lithospheric mantle modified by the Permian Neotethyan Plume//LITHOS Volume: 122 Issue: 1-2 Pages: 122-136 Published: FEB 2011

Middle to Late Triassic lavas were sampled within three tectonostratigraphic groups of the Hawasina Nappes in the Oman Mountains. They are predominantly alkali basalts and trachybasalts, associated with minor sub-alkaline basalts, trachyandesites, trachytes and rhyolites. Their major, trace elements and Nd-Pb isotopic compositions are very similar to those of the Permian plume-related high-Ti basalts which also occur in the Hawasina Nappes. The Triassic lavas derive from low-degree melting of an enriched OIB-type mantle source, characterized by epsilon Nd(i) = 0.3-5.3 and ((206)Pb/(204)Pb)(i) = 16.96-19.31 (for t = 230 My). With time, melting depths decreased from the garnet + spinel to the spinel lherzolite facies and the degree of melting increased. The oldest are distinguished from the others by unradiogenic Nd and Pb signatures, with epsilon Nd(i) = -4.5 to -1.2 and ((209)Pb/(204)Pb)(i) = 16.35-17.08, which we attribute to their contamination by Arabo-Nubian lower crust. The lavas likely derived from the Oman lithospheric mantle, the original DMM-HIMU signature of which was overprinted during its pervasive metasomatism by the Permian plume-related melts. We suggest that these lavas were emplaced during post-breakup decompression-triggered melting in the Middle Triassic during global kinematic reorganization of the Tethyan realm. (c) 2010 Elsevier B.V. All rights reserved.

Chen, Hua-Yong; Chen, Yan-Jing; Baker, Mike Isotopic geochemistry of the Sawayaerdun orogenic-type gold deposit, Tianshan, northwest China: Implications for ore genesis and mineral exploration //CHEMICAL GEOLOGY Volume: 310 Pages: 1-11 Published: JUN 5 2012

The Sawayaerdun gold deposit is hosted by Carbonaceous metasediments and is considered to be the largest Muruntau-type gold deposit in the Chinese Tianshan metallogenic belt. Gold mineralization at Sawayaerdun occurs in quartz veins associated with three major hydrothermal events: an early, barren quartz vein stage, middle stage mineralized quartz veins with pyrite and late carbonate (-quartz) veins. The isotopic compositions of quartz and sulfides from the Sawayaerdun gold deposit show some variation but are generally comparable to those of other orogenic-type gold deposits. Fluids trapped in early-stage quartz have a delta O-18 range of 13.6 parts per thousand to 15.4 parts per thousand, delta D of - 48 parts per thousand. to 7 parts per thousand, delta C-13 of 0.5 parts per thousand. to 4.parts per thousand. and delta Si-30 of - 0.2 parts per thousand to 0 parts per thousand. In contrast, isotopic compositions of fluids trapped in middle-stage quartz have delta O-18 values of 6.7 parts per thousand to 14.7 parts per thousand, delta D of -56 parts per thousand to -110 parts per thousand, delta C-13 of 0.4 parts per thousand. to 10.1 parts per thousand, and delta Si-30 of 0.3 parts per thousand to 0 parts per thousand. Diagenetic and hydrothermal pyrite have similar sulfur (- 1.8 parts per thousand to 0.9 parts per thousand.) and Pb isotopic values that are associated with host rock compositions. The early-stage, O-18 and C-13-rich fluids are probably derived from metamorphic decarbonation of the sedimentary host rock at depth, leading to the precipitation of early barren quartz veins. In the middle stage, a decrease in the regional pressure and temperature regime could have resulted in the incorporation of external fluids into the ore-forming system. These external fluids with isotopic signatures similar to that of the host rock and generally rich in S-34 and radiogenic Pb mixed with original ore-forming fluids to generate extensive metal precipitation. Late-stage fluids trapped by calcite veins show isotopic compositions similar to meteoric water, indicating the cessation of hydrothermal fluid circulation at Sawayaerdun occurred at this time. The metallogenetic model illustrated by stable and Pb isotopes is also consistent with fluid inclusion studies in Sawayaerdun. The development of mineralization at Sawayaerdun is strongly linked to fluid mixing, as witnessed by the isotopic signatures of fluids from identified ore-bearing zones. The isotopic compositions of other anomalous zones at Sawayaerdun are similar to those of the mineralized zones, suggesting a high potential for further exploration. (C) 2012 Elsevier B.V. All rights reserved.

Cooper, Alan F.; Boztug, Durmus; Palin, J. Michael; et al. Petrology and petrogenesis of carbonatitic rocks in syenites from central Anatolia, Turkey//CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 161 Issue: 5 Pages: 811-828 Published: MAY 2011

The late Cretaceous A-type Kara double dagger ayA +/- r pluton in Central Anatolia, Turkey, intrudes and entrains xenoliths of Palaeozoic limestone. Carbonatitic magmatic rocks within the syenite have been previously interpreted (Schuiling in Nature, 192:1280, 1961) to result from metasomatic alteration and syntectic melting of marble. Carbonatites and associated calcite-syenites exhibit mineralogical characteristics (Ab-rich plagioclase, Ba-rich K-feldspar, low-Mg# biotite) that are petrogenetically more evolved than the host syenitic suite. Geochemically, carbonate-rich magmatic rocks are greatly enriched in Sr, Ba, Th, and REE and have higher LREE/HREE ratios than either syenites or marbles. In terms of O-C-Sr-Pb isotope ratios, the carbonatite/calcite-syenite suite form a consistent and geochemically coherent group that is distinct from the marble country rock and xenolith population, but similar to some of the syenitic, and particularly the nepheline syenite components of the Kara double dagger ayA +/- r pluton. Other silicate magmatic rocks are geochemically, isotopically, and geochronologically different, suggesting the pluton is composite. Overall, the mineralogical and geochemical characteristics of the carbonatites are incompatible with binary mixing of syenite and marble but are consistent with derivation of carbonatite from petrogenetically evolved foid syenite. Carbonate-silicate rock types have modal variations compatible with an origin by fractional crystallisation, rather than by liquid immiscibility.

Currie, Claire A.; Beaumont, Christopher Are diamond-bearing Cretaceous kimberlites related to low-angle subduction beneath western North America?//EARTH AND PLANETARY SCIENCE LETTERS Volume: 303 Issue: 1-2 Pages: 59-70 Published: FEB 15 2011

Diamond-bearing Cretaceous kimberlites of western North America were emplaced 1000-1500 km inboard of the Farallon plate subduction margin and overlap with the development of the Western Interior Seaway, shut-down of the Sierra Nevada arc, and the Laramide orogeny. These events are consistent with a decrease in subduction angle along much of the margin, which placed the subducted Farallon plate in close proximity to the continental interior at the time of kimberlite magmatism. Our numerical models demonstrate that low-angle subduction can result from high plate convergence velocities and enhanced westward motion of North America. Further, rapid subduction allows hydrous minerals to remain stable within the cool interior of the subducting plate to more than 1200 km from the trench. Destabilization of these minerals provides a fluid source that can infiltrate the overlying material, potentially triggering partial melting and kimberlite/lamproite magmatism. (C) 2010 Elsevier B.V. All rights reserved.

Demouchy, S.; Mainprice, D.; Tommasi, A.; et al. Forsterite to wadsleyite phase transformation under shear stress and consequences for the Earth's mantle transition zone//PHYSICS OF THE EARTH AND PLANETARY INTERIORS Volume: 184 Issue: 1-2 Pages: 91-104 Published: JAN 2011

We have studied the phase transformation of forsterite to wadsleyite under shear stress at the Earth's transition zone pressure and temperature conditions. Two-step experiments were performed using a multi-anvil press. First, we hot pressed iron-free forsterite at 6 or 11 GPa and 1100 degrees C. Then we deformed a slab of this starting material using a direct simple shear assembly at 16 GPa and 1400 degrees C for 1, 15, 35, 40, or 60 min. Both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations (CPO) by electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The phase transformation occurs very rapidly, in less than 1 min, and metastable forsterite relics are not observed after deformation. The grain size of wadsleyite is slightly smaller than the forsterite starting material. The water contents obtained from FTIR analyses in forsterite and wadsleyite are 65-124 wt ppm H(2)O and 114-736 wt ppm H(2)O, respectively, which are well below water solubility at similar conditions in the presence of free water. Wadsleyite aggregates display weak CPO patterns with [1 0 0] axes concentrated at low angle to the shear direction, [0 1 0] axes perpendicular to the shear plane and nearly random [0 0 1] axes. Only a few dislocations were observed in wadsleyite with TEM. This observation is consistent with the assumption that most dislocations formed during the initial high-stress stages of these stress-relaxation experiments, were consumed in the phase transformation, probably enhancing the transformation rate. CPO patterns vary as a function of the water content: with increasing water content the density of [1 0 0] axes parallel to the shear direction decreases, and the density of [0 0 1] axes increases. Viscoplastic self-consistent modeling of CPO evolution using previously reported glide systems for wadsleyite, i.e., [1 0 0]{0 k 1} and 1/2 (1 1 1){1 0 1}, cannot reproduce the measured CPO, unless the [0 0 1](0 1 0) system, for which dislocations have not been observed by TEM, is also activated. In addition, wadsleyite grain growth suggests the participation of diffusion-assisted processes in deformation. Calculated anisotropies for P and S-waves using measured CPO are always below 1%. This very low anisotropy is due to both the low finite strain achieved in the experiments, which leads to weak wadsleyite CPO, and to the diluting effect of added majorite. The present experiments emphasize the importance of stress, grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone. (C) 2010 Elsevier B.V. All rights reserved.

Donnelly, Cara L.; Griffin, William L.; O'Reilly, Suzanne Y.; et al. The Kimberlites and related rocks of the Kuruman Kimberlite Province, Kaapvaal Craton, South Africa//CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 161 Issue: 3 Pages: 351-371 Published: MAR 2011

The Kuruman Kimberlite Province is comprised of 16 small pipes and dikes and contains some of the oldest known kimberlites (> 1.6 Ga). In this study, 12 intrusions are subdivided into three groups with distinct petrology, age, and geochemical and isotopic compositions: (1) kimberlites with groundmass perovskites defining a Pb-Pb isochron age of 1787 +/- A 69 Ma, (2) orangeite with a U-Pb perovskite age of 124 +/- A 16 Ma, and (3) ultramafic lamprophyres (aillikite and mela-aillikite) with a zircon U-Pb age of 1642 +/- A 46 Ma. The magma type varies across the Province, with kimberlites in the east, lamprophyres in the west and orangeite and ultramafic lamprophyres to the south. Differences in the age and petrogenesis of the X007 orangeite and Clarksdale and Aalwynkop aillikites suggest that these intrusions are probably unrelated to the Kuruman Province. Kimberlite and orangeite whole-rock major and trace element compositions are similar to other South African localities. Compositionally, the aillikites typically lie off kimberlite and orangeite trends. Groundmass mineral chemistry of the kimberlites has some features more typical of orangeites. Kimberlite whole-rock Sr and Nd isotopes show zoning across the Province. When the kimberlites erupted at similar to 1.8 Ga, they sampled a core volume (ca 50 km across) of relatively depleted SCLM that was partially surrounded by a rim of more metasomatized mantle. This zonation may have been related to the development of the adjacent Kheis Belt (oldest rocks similar to 2.0 Ga), as weaker zones surrounding the more resistant core section of SCLM were more extensively metasomatized.

Evidence from detrital zircons for recycling of Mesoproterozoic and Neoproterozoic crust recorded in Paleozoic and Mesozoic sandstones of southern Libya By: Meinhold, Guido; Morton, Andrew C.; Fanning, C. Mark; et al.// EARTH AND PLANETARY SCIENCE LETTERS Volume: 312 Issue: 1-2 Pages: 164-175 Published: DEC 1 2011

The geodynamic history of the Precambrian basement in central North Africa as well as the age and provenance of its sedimentary cover sequence are still poorly constrained. Here we present first detrital zircon ages (obtained by IA-SF-ICP-MS and SHRIMP) from Paleozoic and Mesozoic sandstones of the eastern Murzuq Basin, southern Libya, which unconformably overlie the Saharan Metacraton. Establishing the age and provenance of these sandstones has important implications for our understanding of the evolution of northern Gondwana during the Paleozoic, especially for reconstructions of paleo-source areas and transport paths. Detrital zircons from the sandstones show mainly early Paleozoic to Neoarchean ages with four main age populations, at 2750-2500 Ma (8%), 2200-1750 Ma (16%), 1060-920 Ma (18%), and 720-530 Ma (39%). About 13% of all concordant grains yield ages of 1600-1000 Ma. In addition, there are 9 zircon grains (0.7% of all concordant grains) with ages of 3600-2800 Ma. The presence of a high number of ca. 1 Ga zircons is enigmatic and their origin is controversial. Besides direct sourcing from ca. 1 Ga igneous rocks in eastern Chad and ca. 1 Ga igneous rocks along the southeastern margins of the Congo and Tanzania cratons, recycling of Neoproterozoic sediments containing ca. 1 Ga zircons is another alternative hypothesis to explain the presence of ca. 1 Ga zircons in the Paleozoic sedimentary sequence of central North Africa. The ubiquitous occurrence of ca. 1 Ga zircons in Paleozoic sediments of southern Libya provides insights into the correlation and paleotectonic arrangement of Gondwana-derived terranes, present, for example, in the eastern Mediterranean and in southwestern Europe. Current paleotectonic models of dextral terrane transport along the northern Gondwana margin during the early Paleozoic may need to be revised. (C) 2011 Elsevier B.V. All rights reserved.

Fu, Bin; Kendrick, Mark A.; Fairmaid, Alison M.; et al. New constraints on fluid sources in orogenic gold deposits, Victoria, Australia//CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 163 Issue: 3 Pages: 427-447 Published: MAR 2012

Fluid inclusion microthermometry, Raman spectroscopy and noble gas plus halogen geochemistry, complemented by published stable isotope data, have been used to assess the origin of gold-rich fluids in the Lachlan Fold Belt of central Victoria, south-eastern Australia. Victorian gold deposits vary from large turbidite-hosted 'orogenic' lode and disseminated-stockwork gold-only deposits, formed close to the metamorphic peak, to smaller polymetallic gold deposits, temporally associated with later post-orogenic granite intrusions. Despite the differences in relative timing, metal association and the size of these deposits, fluid inclusion microthermometry indicates that all deposits are genetically associated with similar low-salinity aqueous, CO2-bearing fluids. The majority of these fluid inclusions also have similar Ar-40/Ar-36 values of less than 1500 and Ar-36 concentrations of 2.6-58 ppb (by mass) that are equal to or much greater than air-saturation levels (1.3-2.7 ppb). Limited amounts of nitrogen-rich fluids are present at a local scale and have the highest measured Ar-40/Ar-36 values of up to 5,700, suggesting an external or distinct source compared to the aqueous fluids. The predominance of low-salinity aqueous-carbonic fluids with low Ar-40/Ar-36 values, in both 'orogenic' and 'intrusion-related' gold deposits, is attributed to fluid production from common basement volcano-sedimentary sequences and fluid interaction with sedimentary cover rocks (turbidites). Aqueous fluid inclusions in the Stawell-Magdala deposit of western Victoria (including those associated with N-2) preserve mantle-like Br/Cl and I/Cl values. In contrast, fluid inclusions in deposits in the eastern structural zones, which contain more abundant shales, have elevated molar I/Cl ratios with maximum values of 5,170 x 10(-6) in the Melbourne Zone. Br/I ratios in this zone range from 0.5 to 3.0 that are characteristic of fluid interaction with organic-rich sediments. The maximum I/Cl and characteristic Br/I ratios provide evidence for organic Br and I released during metamorphism of the shales. Therefore, the regional data provide strong evidence for the involvement of sedimentary components in gold mineralisation, but are consistent with deeper metamorphic fluid sources from basement volcano-sedimentary rocks. The overlying sediments are probably involved in gold mineralisation via fluid-rock interaction

Giuliani, A.; Kamenetsky, V. S.; Phillips, D.; et al.Nature of alkali-carbonate fluids in the sub-continental lithospheric mantle//GEOLOGY Volume: 40 Issue: 11 Pages: 967-970 Published: NOV 2012

Mantle xenoliths sampled by kimberlite and alkali basalt magmas show a range of metasomatic styles, but direct evidence for the nature of the metasomatising fluids is often elusive. It has been suggested that carbonate-rich melts produced by partial melting of carbonated peridotites and eclogites play an important role in modifying the composition of the lithospheric mantle. These mantle-derived carbonate melts are often inferred to be enriched in alkali elements; however, alkali-rich carbonate fluids have only been reported as micro-inclusions in diamonds and as unique melts involved in the formation of the Udachnaya-East kimberlite (Yakutia, Russia). In this paper we present the first direct evidence for alkali-carbonate melts in the shallow lithospheric mantle (similar to 110-115 km), above the diamond stability field. These alkali-carbonate melts are preserved in primary multiphase inclusions hosted by large metasomatic ilmenite grains contained in a polymict mantle xenolith from the Bultfontein kimberlite (Kimberley, South Africa). The inclusions host abundant carbonates (magnesite, dolomite, and K-Na-Ca carbonates), kalsilite, phlogopite, K-Na titanates, and phosphates, with lesser amounts of olivine, chlorides, and alkali sulfates. Textural and chemical observations indicate that the alkali-carbonate melt likely derived from primary or precursor kimberlite magmas. Our findings extend the evidence for alkali-carbonate melts/fluids permeating the Earth mantle outside the diamond stability field and provide new insights into the chemical features of previously hypothesized melts. As metasomatism by alkali-rich carbonate melts is often reported to affect mantle xenoliths, and predicted from experimental studies, the fluid type documented here likely represent a major metasomatising agent in the Earth's lithospheric mantle.

Goss, A. R.; Kay, S. M.; Mpodozis, C. The geochemistry of a dying continental arc: the Incapillo Caldera and Dome Complex of the southernmost Central Andean Volcanic Zone (similar to 28 degrees S)//CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 161 Issue: 1 Pages: 101-128 Published: JAN 2011

The Pleistocene Incapillo Caldera and Dome Complex (5,570 m) marks the southernmost siliceous center of the Andean Central Volcanic Zone (similar to 28 degrees S), where the steeply dipping (similar to 30 degrees) segment of the subducting Nazca plate transitions into the Chilean "flatslab" to the south. The eruption of the Incapillo Caldera and Dome Complex began with a 3-1 Ma effusive phase characterized by similar to 40 rhyodacitic dome eruptions. This effusive phase was terminated by an explosive "caldera-forming" event at 0.51 Ma that produced the 14 km(3) Incapillo ignimbrite. Distinctive and virtually identical chemical signatures of the domes and ignimbrites (SiO(2) = 67-72 wt%; La/Yb = 37-56; Ba/La = 16-28; La/Ta = 30-50; (87)Sr/(86)Sr = 0.70638-0.70669; epsilon (Nd) = -4.2 to -4.6) indicate that all erupted lavas originated from the same magma chamber and that differentiation effects between units were minor. The strong HREE depletion (Sm/Yb = 6-8) that distinguishes Incapillo magmas from most of the large ignimbrites of the Altiplano-Puna plateau can be explained by the extent and degree of partial melting at lower crustal depths (> 40 km) in the presence of garnet. At upper crustal depths, this high-pressure residual geochemical signature, also common to adjacent late Miocene/Pliocene Pircas Negras andesites, was partially overprinted by shallow-level assimilation and fractional crystallization processes. Energy-constrained AFC modeling suggests that incorporation of anatectic upper crustal melts into a fractionated "adakite-like" dacitic host best explains the petrogenesis of Incapillo magmas. The diminution of the sub-arc asthenospheric wedge during Nazca plate shallowing left the Incapillo magma chamber unreplenished by both mafic mantle-derived and lower crustal melts and thus stranded at shallow depths within the Andean crust. Based on its small size and distinctive high-pressure chemical signature, the Incapillo Caldera and Dome Complex provides an endmember model for an Andean caldera erupting within a waning magmatic arc over a shallowing subduction zone.

Hettmann, Kai; Kreissig, Katharina; Rehkaemper, Mark; et al.Thallium geochemistry in the metamorphic Lengenbach sulfide deposit, Switzerland: Thallium-isotope fractionation in a sulfide melt //AMERICAN MINERALOGIST Volume: 99 Issue: 4 Pages: 793-803 Published: APR 2014

The Lengenbach (Switzerland) Pb-As-Tl-Zn deposit was formed from a sulfide melt at about 500 degrees C during Alpine metamorphism, but details on its formation and especially the source of the metals are still under debate. In this study we present two sample sets to address these questions: (1) MC-ICP-MS analyses of thallium isotopes in sulfides, sulfosalts, and melt inclusions from the Alpine metamorphic Lengenbach deposit in the Binn Valley of Switzerland, the non-metamorphic Wiesloch Mississippi Valley-type deposit in Southern Germany, and the Cu- and As-rich mineralization at Pizzo Cervandone about 2 km SW of the Lengenbach deposit, which has been discussed as potential source of the Lengenbach metals. (2) LA-ICP-MS analyses of micas from the Lengenbach deposit and surrounding country rocks between the deposit and the Pizzo Cervandone to trace potential metal-bearing fluid pathways. We found that Tl isotope compositions expressed as epsilon Tl-205 values in all investigated samples range from -4.1 +/- 0.5 to + 1.9 +/- 0.5. The whole variation can be seen in the Lengenbach deposit alone, which hence records considerable fractionation even during high-temperature processes involving a sulfide melt. This large range of epsilon Tl-205 is thought to be caused by nuclear volume-dependent fractionation. Interestingly, the common fahlores at Lengenbach behave differently, from all other investigated sulfosalts: based on their heavy isotopic composition together with a low As/S-ratio, they do not seem to be crystallized from the sulfide melt, but are interpreted to have formed from hydrothermal fluids enriched in the heavy Tl isotopes. Although As mobilization in the gneisses and dolomites surrounding the Lengenbach deposit is evident based on secondary arsenites. no traces of such a country rock fluid could be found in fissure micas at Lengenbach. Hence, considerations involving K/Rb, Rb/Tl, As/S, and Pb/Tl ratios in the sulfides and micas imply that the element enrichment in the Lengenbach deposit is either pre-Alpine or related to peak metamorphism, but occurred definitely before mica growth at Lengenbach.

High temperature silicon isotope geochemistry Savage, Paul S.; Armytage, Rosalind M. G.; Georg, R. Bastian; et al.//LITHOS Volume: 190 Pages: 500-519 Published: MAR 2014

Silicon (Si) is the defining element of silicate reservoirs yet, despite its dominance in major Earth processes, there is still no clear understanding of how much is hosted in Earth's core, how the enriched continental crust forms or even if the crust is isotopically different from the mantle because of a long history of weathering, erosion and subduction. With the advent of multiple collector inductively coupled plasma mass spectrometry it has become relatively straightforward to explore small (100 ppm level) mass dependent variations in Si isotopic composition resulting from high temperature fractionation and to develop new isotopic fingerprints of magmatic processes and source regions. This paper reviews the technique developments, the new data and the veracity of current interpretations. Only a small Si isotopic effect is associated with basalt formation via mantle melting. However, there now is compelling evidence, based on a considerable number of samples (> 100), that the silicate Earth is isotopically fractionated by 100-200 ppm per amu to a heavy composition relative to that of chondrites and also all differentiated stony meteorites. This could reflect variability in the circumstellar disc, but this is not well supported by data for enstatite chondrites which are isotopically light. The most plausible current explanation is that Si is a light element in Earth's core and that differences in the bond stiffness between silicate- and metal-hosted Si resulted in substantial fractionation. Interestingly, the Moon has the same Si isotope composition as Earth's mantle, which is hard to explain unless the Moon's atoms were mainly derived from Earth. Differentiated magmatic sequences such as those of Hekla, Iceland display a systematic relationship between isotopic composition and Si content. More complex magmatic suites, such as I- and S-type granites, reveal a range of isotopic compositions not well correlated with chemical composition. Similar effects are found in lower crustal granulite facies xenoliths. Nonetheless the overall composition of the continental crust is only slightly heavy relative to the mantle; in fact the effect is barely resolvable. Therefore, the amounts of surface dissolved heavy Si removed to the mantle via weathering over time have been small or these losses have been balanced by subduction of isotopically light clay. (C) 2014 Elsevier B.V. All rights reserved.

Hou, Tong; Zhang, Zhaochong; Encarnacion, John; et al. The role of recycled oceanic crust in magmatism and metallogeny: Os-Sr-Nd isotopes, U-Pb geochronology and geochemistry of picritic dykes in the Panzhihua giant Fe-Ti oxide deposit, central Emeishan large igneous province, SW China//CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 165 Issue: 4 Pages: 805-822 Published: APR 2013

The picritic dykes occurring within fine-grained gabbro in the marginal zone and in the surrounding Proterozoic wall-rock marbles of the Panzhihua Fe-Ti oxide deposit closely correspond in bulk composition with the nearby Panzhihua intrusion. These dykes offer important constraints on the nature of the mantle source of the Panzhihua ore-bearing intrusion and its possible link to the Emeishan plume. U-Pb zircon dating of the picritic dyke yields a crystallization age of 261.4 +/- A 4.6 Ma, coeval with the timing of the main Panzhihua gabbroic intrusion and Late Permian Emeishan flood basalts. The Panzhihua picritic dykes contain 37.63-43.41 wt% SiO2, 1.15-1.56 wt% TiO2, 11.43-13.25 wt% TFe2O3, and 20.96-28.87 wt% MgO. Primitive-mantle-normalized patterns of the rocks are comparable to those of ocean island basalt. The rocks define a relatively small range of Os isotopic compositions and a low Os signature of -0.13 to +2.76 for gamma(Os) (261 Ma). In combination with their Sr-Nd-Os isotopic compositions, we interpret that these rocks were derived from the Emeishan plume sources as well as the interactions of plume melts with the overlying lithosphere which had been extensively affected by eclogite-derived melts from the deep-subducted oceanic slab. Partial melting induced by an upwelling mantle plume that involved an eclogite or pyroxenite component in the lithospheric mantle could have produced the parental Fe-rich magma. Our study suggests that plume-lithosphere interaction might have played a key role in generating many world-class Fe-Ti oxide deposits clustered in the Panxi area.

Jung, S.; Pfaender, J. A.; Brauns, M.; et al.Crustal contamination and mantle source characteristics in continental intra-plate volcanic rocks: Pb, Hf and Os isotopes from central European volcanic province basalts /GEOCHIMICA ET COSMOCHIMICA ACTA Volume: 75 Issue: 10 Pages: 2664-2683 Published: MAY 15 2011

We report new Os-Pb-Hf isotope data for a suite of alkaline to basaltic (nephelinites, basanites, olivine tholeiites to quartz-tholeiites) lavas from the Miocene Vogelsberg (Germany), the largest of the rift-related continental volcanic complexes of the Central European Volcanic Province (CEVP). Os-187/Os-188 in primitive (high-MgO) alkaline lavas show a much wider range than has been observed in alkaline basalts and peridotite xenoliths from elsewhere in the CEVP, from ratios similar to those in modern MORB and OIB (0.1260-0.1451; 58.9-168 ppt Os) to more radiogenic ratios (0.1908 and 0.2197; 27.6-15.1 ppt Os). Radiogenic Os is associated with high epsilon(Hf) and epsilon(Nd), low Sr-87/Sr-86 and does not correlate with Mg* or incompatible trace elements (e. g. Ce/Pb), suggesting the presence of a radiogenic endmember in the mantle rather than crustal contamination as the source of radiogenic Os. This contrasts with another high-Mg alkaline lava characterized by highly radiogenic Os-187/Os-188 (0.4344, 10.3 ppt Os), lower epsilon(Hf) and epsilon(Nd), higher Sr-87/Sr-86, and Pb isotope signatures than the other alkaline lavas with similar trace element composition suggestive of contamination with crustal material. Hafnium (eHf: + 8.9 to + 5.0) and Pb isotope compositions (Pb-206/Pb-204: 19.10-19.61; Pb-207/Pb-204: 15.56-15.60) of the alkaline rocks fall within the range of enriched MORB and some OIB. The Vogelsberg tholeiites show even more diverse Os-187/Os-188, ranging from 0.1487 in Os-rich olivine tholeiite (31.7 ppt) to ratios as high as 0.7526 in other olivine-tholeiites and in quartz-tholeiites with lower Os concentrations (10.3-2.0 ppt). Low-Os-187/Os-188 tholeiites show Pb-Hf isotope ratios (Pb-206/Pb-204: 18.81; Pb-207/Pb-204: 15.61; epsilon(Hf): + 2.7) that are distinct from those in alkaline lavas with similar Os-187/Os-188 and originate from a different mantle source. By contrast, the combination of radiogenic Os and low Pb-206/Pb-204 and epsilon(Hf) in the other tholeiites probably reflects crustal contamination. The association at Vogelsberg of primitive alkaline and tholeiitic lavas with a range of MORB- to OIB-like Os-Pb-Hf-Nd-Sr isotopic characteristics requires at least two asthenospheric magma sources. This is consistent with trace element modelling which suggests that the alkaline and tholeiitic parent magmas represent mixtures of melts from garnet and spinel peridotite sources (both with amphibole), implying an origin of the magmas in the garnet peridotite-spinel peridotite transition zone, probably at the asthenosphere-lithosphere interface. We propose that uncontaminated Vogelsberg lavas originated in 'metasomatized' mantle, involving a 3-stage model: (1) early carbonatite metasomatism several 10-100 Ma before the melting event (2) deposition of low-degree asthenospheric melts from carbonated peridotite at the lithosphere-asthenosphere thermal boundary produces hydrous amphibole-bearing veins or patches, and (3) remobilization of this modified lithospheric mantle into other asthenospheric melts passing through the same area later. In keeping with 'metasomatized' mantle models for other continental basalt provinces, we envisage that stage (2) is short-lived (few Ma), thus producing a prominent lithospheric trace element signature without changing the asthenospheric isotopic signatures. Models of this type can explain the peculiar mix of lithospheric (prominent depletions of Rb and K) and asthenospheric (OIB-like high Os-187/Os-188, Nd-143/Nd-144 and Hf-176/Hf-177) signatures observed in the Vogelsberg and many other continental basalt suites. (C) 2011 Elsevier Ltd. All rights reserved.

Kogarko, L. N.Geochemistry of radioactive elements in the rocks of the Guli Massif, Polar Siberia //GEOCHEMISTRY INTERNATIONAL Volume: 50 Issue: 9 Pages: 719-725 Published: SEP 2012

The study of radioactive element distribution in the rocks of the Guli Complex revealed an increase of uranium and thorium contents in the final products of magmatic differentiation. In the carbonatite complex, the radioactive elements are mainly accumulated in the early rocks-phoscorites, while their contents in the late phases, dolomitic carbonatites, decrease. The Th/U ratio increases from near-chondritic values in the weakly differentiated highly-magnesian primary magmas to the late rocks-phoscorites, calcitic carbonatites, and dolomitic carbonatites. The majority of radioactive elements are hosted in rare-metal accessory minerals: perovskite, pyrochlore, calzirtite, and apatite. Rock-forming minerals are characterized by extremely low contents of radioactive elements.

Leng, Cheng-Biao; Huang, Qiu-Yue; Zhang, Xing-Chun; et al. Petrogenesis of the Late Triassic volcanic rocks in the Southern Yidun arc, SW China: Constraints from the geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes //LITHOS Volume: 190 Pages: 363-382 Published: MAR 2014

Studies on zircon ages, petrology, major and trace element geochemistry, and Sr-Nd-Hf-Pb isotopic geochemistry of intermediate volcanic rocks from the Southern Yidun arc, Sanjiang-Tethyan Orogenic Belt, SW China have been undertaken in this paper. They are used to discuss the petrogenesis of these rocks and to constrain the tectonic setting and evolution of the Yidun arc. These intermediate volcanic rocks were erupted at ca. 220 Ma (U-Pb zircon ages). Trachyandesite is the dominant lithology among these volcanic rocks, and is mainly composed of hornblende and plagioclase, with minor clinopyroxene and biotite. A hornblende geobarometer suggests that the stagnation of magma in the lower crust, where plagioclase crystallization was suppressed while hornblende crystallized, giving rise to high Sr/Y ratios that are one of the distinguishing features of adakites, after the primary magma originated from the lithospheric mantle wedge. Steeply right-inclined Rare Earth Element (REE) pattern combined with high La/Yb ratios suggests adakitic affinity of these volcanic rocks, implying that slab-melt from the subducting oceanic crust is a necessary component in the primary magma. Besides, trace element geochemistry and isotopic geochemistry also indicate that partial melting of pelagic sediments in the subduction zone and noticeable contamination with the lower crust were involved in the evolution of parental magma of these volcanic rocks. Based on previous work on the Northern Yidun arc and this study, we propose that the subduction was initiated in the Northern Yidun arc and extended to the southern part and that the Northern Yidun arc is an island arc while the Southern Yidun arc represents a continental arc, probably caused by the existence of the Zhongza Massif, that was invoked to be derived from Yangtze Block, as a possible basement of the Southern Yidun arc. (C) 2013 Elsevier B.V. All rights reserved.


The mechanism for the widespread Mesozoic magmatism in South China has been ascribed to either the paleo-Pacific plate subduction or intra-continental lithospheric extension. Mantle xenoliths entrained in the Jurassic Ningyuan alkaline basalts from southern Hunan Province, including twelve lherzolites and one harzburgite, have been studied to constrain the composition and age of the Mesozoic sub-continental lithospheric mantle. The lherzolites contain 2.06-4.09 wt.% Al2O3 and 2.03-3.91 wt.% CaO, which are higher than the abundances of these species in the harbzurgite (1.72 wt.% and 1.17 wt.%, respectively). The Cr# of spinel varies from 0.07 to 0.24. Orthopyroxene contains 3.61-4.96 wt.% Al2O3 and 0.51-0.8 wt.% CaO, whereas clinopyroxene contains 4.78-7.32 wt.% Al2O3 and 1.04-2.01 wt.% Na2O. Both whole rock and mineral compositions suggest that the Ningyuan mantle xenoliths have been subjected to low degrees of partial melting. Modeling of Y and Yb contents of clinopyroxene indicates that the lherzolites have been subjected to 3-5% degrees of partial melting, while the harzburgite has experienced about 12% melting. Clinopyroxene in most Ningyuan mantle xenoliths shows variable depletion in incompatible elements, suggesting that they have been weakly enriched after melting. Clinopyroxene in one sample (TYS01-3) displays strong enrichment in incompatible elements, reflecting the local occurrence of melt metasomatism. Equilibrium temperatures estimated by two-pyroxene geothermometry vary from 994 to 1081 degrees C. indicating that the Mesozoic mantle lithosphere has a hot geotherm. All Iherzolites display consistent highly siderophile element (HSE) patterns and have suprachondritic Ru/Ir and Pd/Ir ratios. The harzburgite shows remarkable depletion in Pt, Pd and Re. The lherzolites have Os-187/Os-188 ratios of 0.12116-0.12929, which are higher than that of the harzburgite (0.11681). A correlation between Os-187/Os-188 and Al2O3 exists among the Ningyuan mantle xenoliths, which if interpreted as an isochron analog yields a model age of similar to 2.2 Ga. This age is older than the Re depletion age (T-RD) of the harzburgite (similar to 1.8 Ga), which represents a minimum age of melt depletion. The old ages either support the existence of ancient lithosphere relics beneath the Ningyuan region or reflect the accretion of ancient mantle materials from the asthenosphere during the Mesozoic. Although the tectonic implication of the old ages is ambiguous, compositions of the Ningyuan mantle xenoliths suggest that ancient mantle lithosphere beneath South China has been thinned and replaced by hotter, younger mantle during the Mesozoic, which has led to extensive lithospheric extension and abundant magmatism. (C) 2011 Elsevier B.V. All rights reserved.

Liu Xiujin; Liu Wei Source characteristics and tectonic setting of the Early and Middle Devonian volcanic rocks in the North Junggar, Northwest China: Insights from Nd-Sr isotopes and geochemistry //LITHOS Volume: 184 Pages: 27-41 Published: JAN 2014

Andesite and pyroxene diorite porphyry in the North Junggar, NW China yield zircon U-Pb age of 412.9 +/- 1.7 Ma and 380.7 +/- 3.8 Ma, suggesting that they were formed in the Early and Middle Devonian. The Early Devonian lavas consist of basalt, basaltic andesite and andesite, dacitic porphyry and rhyolite. The enrichment of LILE and LREE, remarkably negative Nb, Ta and Ti anomalies, and low (Sr-87/Sr-86)(i) ratios and high epsilon(Nd)(t) values in these volcanic rocks, indicate that the Early and Middle Devonian igneous rocks were formed in an intraoceanic arc, and no continental crust was involved. The wide range of lava types, abundant phenocrysts and overall chemical and isotopic coherence of the Early Devonian lavas clearly suggest that fractional crystallization was the dominant process controlling the evolution of Early Devonian lavas, and is accompanied by the reinjection of parental melt into the magma chamber which can be clearly verified by reverse zoning of plagioclase phenocrysts and their abrupt increase of An content from sieved-textured core to rim. Andesite and basaltic andesite displaying adakitic characteristics have negligible relation to melting of subducted basaltic crust; instead, they are products of basaltic replenishment and fractional crystallization of plagioclase + clinopyroxene + hornblende from mafic magmas. The mantle source of Early Devonian lavas was enriched by much more slab-derived component than that of pyroxene diorite porphyry. With the evolvement of an island arc, involvement of slab-derived components in arc magmatism could decrease; moreover, the high-level crustal contamination may be a more important mechanism than source enrichment. (C) 2013 Elsevier B.V. All rights reserved.

Liu, Q. Y.; Worden, R. H.; Jin, Z. J.; et al. SR versus non-TSR processes and their impact on gas geochemistry and carbon stable isotopes in Carboniferous, Permian and Lower Triassic marine carbonate gas reservoirs in the Eastern Sichuan Basin, China //GEOCHIMICA ET COSMOCHIMICA ACTA Volume: 100 Pages: 96-115 Published: JAN 1 2013

Deep-sea bamboo corals hold promise as long-term climatic archives, yet little information exists linking bamboo coral geochemistry to measured environmental parameters. This study focuses on a suite of 10 bamboo corals collected from the Pacific and Atlantic basins (250-2136 m water depth) to investigate coral longevity, growth rates, and isotopic signatures. Calcite samples for stable isotopes and radiocarbon were collected from the base the corals, where the entire history of growth is recorded. In three of the coral specimens, samples were also taken from an upper branch for comparison. Radiocarbon and growth band width analyses indicate that the skeletal calcite precipitates from ambient dissolved inorganic carbon and that the corals live for 150-300 years, with extension rates of 9-128 mu m/yr. A linear relationship between coral calcite delta O-18 and delta C-13 indicates that the isotopic composition is influenced by vital effects (delta O-18:delta C-13 slope of 0.17-0.47). As with scleractinian deep-sea corals, the intercept from a linear regression of delta O-18 versus delta C-13 is a function of temperature, such that a reliable paleotemperature proxy can be obtained, using the "lines method." Although the coral calcite delta O-18:delta C-13 slope is maintained throughout the coral base ontogeny, the branches and central cores of the bases exhibit delta O-18:delta C-13 values that are shifted far from equilibrium. We find that a reliable intercept value can be derived from the delta O-18:delta C-13 regression of multiple samples distributed throughout one specimen or from multiple samples within individual growth bands.


This study integrates new and extant zircon U-Pb age and Hf isotope data, whole-rock Nd-Sr isotope data, and geochemistry data from the Chinese Altay (CA) and adjacent areas, in an attempt to identify the source rocks of granitoids and acidic-intermediate volcanic rocks and, hence, continental-crust growth in the CA. The protolith of the gneisses includes the earliest products of erosion from the surface rocks of the island arc volcanics and the syn- and post-collisional granitoids of the Caledonian orogenic-mountain system, whereas the provenance of metasedimentary rocks was exposed from increasingly deeper levels or from an expanded region that evolved from the axis to the flank of the mountain system as it was denuded until planation such that eroded material from the Tuva-Mongol microcontinental block to the east could be delivered to the CA. The CA tends to be more mafic and isotopically more primitive with depth, because material eroded early constitutes the lower section and material eroded late constitutes the upper section of the Early-Paleozoic sedimentary-pile. Source rocks for the granitoids and acidic-intermediate volcanic rocks of the CA include the eroded material from the microcontinental block, the eroded material from the syn- and post-collisional granitoids of the Caledonian province, MORB-type mafic rocks, and a minor component from the metasomatized lithospheric-mantle. Eroded material from the terrains north of the CA was first deposited as an Early-Paleozoic sedimentary-pile in the CA. The top section of this pile was again eroded and transported to the trench at the CA continental margin, and these second-round sediments were subducted beneath the CA accretionary wedge. The un-eroded lower section of the Early-Paleozoic sedimentary-pile lay at bottom of the CA accretionary wedge that was underplated by MORB-type mafic rocks. The CA granitoids can be divided into orogenic (460-360 Ma) and post-orogenic (similar to 320-260 Ma). The orogenic granitoids can be subdivided into Groups 1 (epsilon(Nd) (t) < +1) and 2 (epsilon(Nd) (t) mostly higher than +1). The main branch of the granitoids (67 data) that includes Group 1 and a majority of Group 2 were derived mainly from eroded materials from the Caledonian province and the Tuva-Mongol microcontinental block. The source rock of acidic-intermediate volcanic rocks was dominantly eroded materials from the latter. The granitoids in the Erqisi nappe at the junction between the CA and the Junggar are characterized by a mixed source between MORB-like mafic rocks and juvenile crustal-rocks. The Mid-Devonian dacite-rhyolite and dolerite dikes in the west Chinese Altay were derived from metasomatized lithospheric-mantle. Integrated isotope and geochemistry data further constrain the source compositions of granitoids. The granitoids in the northwest Chinese Altay were mainly derived from subducted sediment that was eroded from the top section of the Early-Paleozoic sedimentary-pile, whereas those in the east Chinese Altay were derived dominantly from the lower section of the pile. The source rock of the granitoids in the northeast of the middle Chinese Altay consists of the lower section of the Early-Paleozoic sedimentary-pile; and sediment, quartz keratophyre, and keratophyre that were subducted or thrust beneath the northern Chinese Altay. The main source rock of the granitoids in the southwest of the middle Chinese Altay varies between the subducted sediment in the westernmost segment and the lower section of the Early-Paleozoic sedimentary-pile and the mafic underplate to the east. A geophysical-sounding profile across the CA and East Junggar reveals a three-layer structure of the CA accretionary-wedge underplated by an oceanic lithosphere that was detached from the downgoing oceanic-spreading-center. From the Silurian to the Mid-Late Devonian, the active spreading-center was repeatedly subducted beneath the CA along a southwestward-retreating subduction zone as

Mani, Devleena; Patil, D. J.; Dayal, A. M. Stable carbon isotope geochemistry of adsorbed alkane gases in near-surface soils of the Saurashtra Basin, India //CHEMICAL GEOLOGY Volume: 280 Issue: 1-2 Pages: 144-153 Published: JAN 7 2011

Fifteen samples with high concentrations of alkane gases were measured for their delta C-13(1); delta C-13(2) and delta C-13(3) compositions using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The values for methane varied from -27 to -45.4 parts per thousand, ethane from -20.9 to -27.6 parts per thousand, and propane from -20.4 to -29.1 parts per thousand versus the Vienna PeeDee Belemnite (VPDB). The carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gases derived from thermogenic sources. Comparisons of carbon isotopic signatures and compositional variations with the standard carbon isotopic models suggest that hydrocarbon gases found in the shallow depths of the study area are not of bacterial origin but are formed thermally from deeply buried organic matter, likely to be mainly a terrestrial source rock with a partial contribution from a marine source. These gases may have migrated to the near-surface environment, where they represent an admixture of thermally generated hydrocarbon gases from mixed sources and maturity. The maturity scale (delta C-13 versus Log Ro %) applied to the surface sediment samples of the Jamnagar area indicated the source material to be capable of generating oil and gas. The detection of thermogenic alkane gases in near-surface sediments offers the possibility of hydrocarbons at depth in Saurashtra. (C) 2010 Elsevier B.V. All rights reserved.

Mao, Qigui; Xiao, Wenjiao; Fang, Tonghui; et al. Geochronology, geochemistry and petrogenesis of Early Permian alkaline magmatism in the Eastern Tianshan: Implications for tectonics of the Southern Altaids//LITHOS Volume: 190 Pages: 37-51 Published: MAR 2014

In the early Permian large volumes of volcanic rocks developed in the Eastern Tianshan of the southern Altaids. The Shaerhu alkaline complex, which occurs along a NW-trending transcurrent fault in the Dananhu arc, is composed of alkaline gabbro intrusions, granites and rhyolites; the gabbros and rhyolites have similar zircon crystallization ages of 286.5 +/- 2.1 Ma and 286.7 +/- 2.1 Ma, respectively. The granitic and rhyolitic rocks have typical A-type granite geochemical signatures, i.e. high oxide ratios (in wt.%): K2O + Na2O, (K2O + Na2O)/CaO, K2O/MgO, and SiO2, high trace element values: Zr, Nb, Ga, Ce, Y, and REE, and high Zr + Ce + Y, and 10,000 * Ga/Al ratios. However, spidergrams and REE patterns indicate major depletions in Ba, Sr, P. Ti and Eu. The presence of positive epsilon(Nd)(t) values of + 7.0 to +11.2 and low (Sr-87/Sr-86)(i) (0.70148-0.70416) indicates that these alkaline rocks were derived from a depleted mantle, and not from old continental crust. The geochemical characters indicate that the rocks of the complex have the same source and that fractionation was important in their generation. A-type granitic rocks are the most highly fractionated of alkaline basic rocks. In summary, the Shaerhu complex is a product of mantle-derived alkaline magma fractionation, which is one of the main mechanisms of A-type granite genesis. The felsic rocks of the Shaerhu complex have the geochemical signature of an A(2)-type granite, and thus were not derived from a rift or mantle plume. In the early Permian, oblique subduction in the southern Altaids gave rise to strike-slip extensional faults, which controlled the emplacement of large volumes of mantle-derived melts. (C) 2013 Elsevier B.V. All rights reserved.

Marks, Michael A. W.; Hettmann, Kai; Schilling, Julian; et al.The Mineralogical Diversity of Alkaline Igneous Rocks: Critical Factors for the Transition from Miaskitic to Agpaitic Phase Assemblages //JOURNAL OF PETROLOGY Volume: 52 Issue: 3 Pages: 439-455 Published: MAR 2011

Geochemically, the large family of alkaline plutonic rocks (both Qtz-undersaturated and -oversaturated compositions) can be subdivided into metaluminous [(Na2O + K2O) < Al2O3] and peralkaline [(Na2O + K2O) > Al2O3] types. In this paper, we discuss two important aspects of the mineralogical evolution of such rocks. With respect to their Fe-Mg phases, a major mineralogical transition observed is the precipitation of arfvedsonite or aegirine instead of fayalite or magnetite (+/- ilmenite). The relative stability of these phases is controlled by oxygen fugacity and Na activity in the crystallizing melts. If Na activity in the melt is high enough, arfvedsonite + aegirine form a common assemblage in peralkaline rocks under both reduced and oxidized conditions. Major mineralogical differences within this rock group exist with respect to their high field strength element (HFSE)-rich minerals: most syenitic rocks, known as miaskites, contain zircon, titanite or ilmenite as HFSE-rich minerals, whereas in agpaites complex Na-K-Ca-(Ti, Zr) silicates incorporate the HFSE. Similarly, only a small group of peralkaline granites are found to lack zircon, titanite or ilmenite but instead contain Na-K-Ca-(Ti, Zr) silicates. Here, we present a detailed phase petrological analysis of the chemical parameters (mu Na2O, mu CaO, mu K2O) that influence the transition from miaskitic to agpaitic rocks. Based on the occurrence of Ti and Zr minerals, several transitional mineral assemblages are identified and two major evolution trends for agpaites are distinguished: a high-Ca trend, which is exemplified by the alkaline rocks of the Kola Province, Russia, and a Ca-depletion trend, which is displayed by the alkaline rocks of the Gardar Province, South Greenland. Both trends show significant Na-enrichment during magmatic evolution. High-Ca agpaites evolve from nephelinitic parental melts that did not crystallize large amounts of plagioclase. In contrast, agpaites showing Ca-depletion originate by extensive fractionation of plagioclase from basaltic parental melts. In some peralkaline granites evolutionary trends are observed that culminate in agpaite-like HFSE-mineral associations in the most evolved rocks.

Mattioli, Michele; Lustrino, Michele; Ronca, Sara; et al. Alpine subduction imprint in Apennine volcaniclastic rocks. Geochemical-petrographic constraints and geodynamic implications from Early Oligocene Aveto-Petrignacola Formation (N Italy)//LITHOS Volume: 134 Pages: 201-220 Published: MAR 2012

The present-day northern Apennines represent an area where two different orogenic cycles took place. The most ancient is the Alpine Orogeny, initiated with a south- to south-eastward subduction of oceanic lithosphere (Early Cretaceous to Late Eocene phase), followed by continental collision. The younger is referred to the Apennines Orogeny, characterized by a west- to north-westward oceanic lithosphere subduction started from Late Eocene and still active in the southemmost sectors of Italy (Calabrian Arc). In this framework, during the Early Oligocene, an similar to 800 m thick conglomeratic succession extremely rich in volcanic material (up to similar to 90% in volume) was deposited in the Northern Apennines, forming the Aveto-Petrignacola Formation (APF). The volcanic fraction of this succession is made up of basaltic andesites, andesites and dacites, with minor rhyolites, basalts and gabbros found as pebbles -0.001-0.5 m(3) in size. Petrographic, mineral chemical, major and trace element analyses, as well as Sr-Nd-Pb isotopic ratios are compatible with calc-alkaline magmatism generated as a consequence of metasomatic modifications related to the subduction of oceanic lithosphere. The large spectrum of lithologies is compatible with processes of fractional crystallization of the main phases observed in thin sections. However, the large range of isotopic ratios (Sr-87/Sr-86 = 0.7044-0.71013; Nd-143/Nd-144 = 0.51278-0.51223; Pb-206/Pb-204 = 18.44-18.83; (207)pb/(204)pb = 15.55-15.67; Pb-208/Pb-204 = 38.05-38.85) suggests the presence of heterogeneous mantle sources, possibly coupled with interaction of melts with crustal rocks at shallow depth. On the basis of field geology constraints, we propose that the subduction-related geochemical and mineralogical characteristics of the APF volcanic rocks reflect ancient modifications of their mantle sources, lacking any evidence for a genetic link with the Apennine subduction system. Subduction-related metasomatism of APF mantle sources likely occurred during the older south-east dipping subduction of the Alpine Tethys under Northern Adria (present day Northern Italy). (C) 2012 Elsevier B.V. All rights reserved.

McCreath, Jamie A.; Finch, Adrian A.; Herd, Donald A.; et al Geochemistry of pyrochlore minerals from the Motzfeldt Center, South Greenland: The mineralogy of a syenite-hosted Ta, Nb deposit // AMERICAN MINERALOGIST Volume: 98 Issue: 2-3 Pages: 426-438 Published: FEB-MAR 2013

Vladykinite, ideally Na3Sr4(Fe2+Fe3+)Si8O24, is a new complex sheet silicate occurring as abundant prismatic crystals in a dike of coarse-grained peralkaline feldspathoid syenite in the north-central part of the Murun complex in eastern Siberia, Russia (Lat. 58 degrees 22 ' 48 '' N; Long. 119 degrees 03 ' 44 '' E). The new mineral is an early magmatic phase associated with aegirine, potassium feldspar, eudialyte, lamprophyllite, and nepheline; strontianite (as pseudomorphs after vladykinite) and K-rich vishnevite are found in the same assemblage, but represent products of late hydrothermal reworking. Vladykinite is brittle, has a Mohs hardness of 5, and distinct cleavage on {100}. In thin section, it is colorless, biaxial negative [alpha = 1.624(2), beta = 1.652(2), gamma = 1.657(2), 2V(meas) = 44(1)degrees, 2V(calc) = 45(1)degrees] and shows an optic orientation consistent with its structural characteristics (X<^>a = 5.1 degrees in beta obtuse, Z<^>c = 4.7 degrees in beta acute, Y = b). The Raman spectrum of vladykinite consists of the following vibration modes (listed in order of decreasing intensity): 401, 203, 465, 991, 968, 915, 348, 167, 129, 264, 1039, and 681 cm(-1); O-H signals were not detected. The Mossbauer spectrum indicates that both Fe2+ and Fe3+ are present in the mineral (Fe3+/Fe-Sigma = 0.47), and that both cations occur in a tetrahedral coordination. The mean chemical composition of vladykinite (acquired by wavelength-dispersive X-ray spectrometry and laser-ablation inductively-coupled-plasma mass-spectrometry), with Fe-Sigma recast into Fe2+ and Fe3+ in accord with the Mossbauer data, gives the following empirical formula calculated to 24 O atoms: (Na2.45Ca0.56)(Sigma 3.01)(Sr-3.81 1(K0.04Ba0.02La0.02Ce0.01)Sigma(3.90)(Fe0.752+Fe0.663+Mn0.26Zn0.26Al0.12Mg0.05Ti0.01)(Sigma 2.01)(Si7.81Al0.19)(Sigma 8.00)O-24. The mineral is monoclinic, space group P2(1)/c, a = 5.21381(13), b = 7.9143(2), c = 26.0888(7) angstrom, beta = 90.3556(7)degrees, V = 1076.50(5) angstrom(3), Z = 2. The ten strongest lines in the powder X-ray diffraction pattern are [d(obs) in angstrom (I) (hkl)]: 2.957 (100) ((1) over bar 23, 123); 2.826 (100) ((1) over bar 17, 117); 3.612 (58) ((1) over bar 14, 114); 3.146 (37) (120); 2.470 (32) (210, 01.10); 4.290 (30) ((1) over bar 11, 111); 3.339 (30) ((1) over tilde 06, 115, 106); 2.604 (28) (200); 2.437 (25) (034); 1.785 (25) (21.10, 234). The structure of vladykinite, refined by single-crystal techniques on the basis of 3032 reflections with F-o > 4 sigma F-o to R-1 = 1.6%, consists of tetrahedral sheets parallel to (100) and consisting of (Si8O24)(16-) units incorporating four-membered silicate rings and joined into five- and eight-membered rings by sharing vertices with larger tetrahedra hosting Fe2+, Fe3+, Mn, Zn, Al, Mg, and Ti. Larger cations (predominantly Na, Sr, and Ca) are accommodated in octahedral and square-antiprismatic interlayer sites sandwiched between the tetrahedral sheets.

Merle, Renaud; Kaczmarek, Mary-Alix; Tronche, Elodie; et al. Occurrence of inherited supra-subduction zone mantle in the oceanic lithosphere as inferred from mantle xenoliths from Dragon Seamount (southern Tore-Madeira Rise)//JOURNAL OF THE GEOLOGICAL SOCIETY Volume: 169 Issue: 3 Pages: 251-267 Published: MAY 2012

Spinel-bearing peridotite and pyroxenite xenoliths dredged from the Dragon Seamount (southern Tore-Madeira Rise, West Iberia and Morocco margin) give an insight into the composition of the underlying lithosphere. These xenoliths are devoid of evidence of strong host lava-peridotite interaction and re-equilibration or late impregnation in the plagioclase facies. The spinels and pyroxenes from the Dragon peridotites have compositions distinct from those of both Iherzolites and harzburgites from the Iberia margin and the Mid-Atlantic Ridge. They display a highly depleted composition, in particular, high Cr-number, up to 0.63 in the spinels, consistent with a melting degree between 12 and 19%. Because of the strong chemical similarities between the Tore-Madeira Rise, Newfoundland peridotites, and peridotites from supra-subduction zones, we propose that the Dragon peridotites formed in a similar context. The pyroxenites display a cumulate texture and are probably a high-temperature-high-pressure cumulate formed by fractional crystallization from a melt. The Tore-Madeira Rise peridotites may represent a former mantle wedge in an oceanic arc, later included into the continental lithosphere and finally tectonically disseminated within the lithosphere during the rifting of the Newfoundland-Iberia continental lithosphere. As a consequence, rifting processes may produce heterogeneities in the oceanic lithosphere and influence isotopic compositions of ocean island basalt-type lavas during plume-lithosphere interactions, as inferred for the southern Tore-Madeira Rise.

Mollo, Silvio; Putirka, Keith; Iezzi, Gianluca; et al. The control of cooling rate on titanomagnetite composition: implications for a geospeedometry model applicable to alkaline rocks from Mt. Etna volcano// CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 165 Issue: 3 Pages: 457-475 Published: MAR 2013

In this study, we have investigated the control of cooling rate on the composition of titanomagnetite formed from a trachybasaltic melt. Results show that disequilibrium growth conditions exert a primary control on the abundance, texture, and composition of the crystals. As the degree of cooling is increased, titanomagnetites show immature textures and are progressively enriched in Al + Mg and depleted in Ti. Thus, early-formed titanomagnetite nuclei do not re-equilibrate with the melt over faster cooling rates; instead, their compositions are far from equilibrium. On the basis of the different intra-crystal redistribution rates for Ti, Al, and Mg, we have calibrated a geospeedometer that represents the first quantitative description of the effect of cooling rate on titanomagnetite composition. This model was tested using the compositions of titanomagnetites in lava and dike samples from Mt. Etna volcano whose crystallization conditions resemble those of our experiments. Cooling rates calculated for lava samples are comparable with those measured in several volcanic complexes. At Mt. Etna, compositional variations of titanomagnetite grains from the innermost to the outermost part of a dike testify to progressively higher degrees of cooling, in agreement with numerical simulations of thermal gradients in and around magmatic intrusions.

Moore, Nicole E.; DeBari, Susan M. Mafic magmas from Mount Baker in the northern Cascade arc, Washington: probes into mantle and crustal processes // CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 163 Issue: 3 Pages: 521-546 Published: MAR 2012

Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt of Park Butte (49.3-50.3 wt% SiO2, Mg# 64-65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of Lake Shannon (50.7-52.6 wt% SiO2, Mg# 58-62) and Sulphur Creek (51.2-54.6 wt% SiO2, Mg# 56-57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8-54.0 wt% SiO2, Mg# 68-70) and the HMA of Glacier Creek (58.3-58.7 wt% SiO2, Mg# 63-64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO2 suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite unit, Cathedral Crag (52.2-52.6 wt% SiO2, Mg# 55-58), is an Mg-poor differentiate of the Type 3 endmember. The calc-alkaline lavas are least enriched in a subduction component (lowest H2O, Sr/P-N, and Ba/Nb), the LKOT-like lavas are intermediate (moderate Sr/P-N and Ba/Nb), and the HMBA are most enriched (highest H2O, Sr/P-N and Ba/Nb). The generation of the LKOT-like and calc-alkaline lavas can be successfully modeled by partial melting of a spinel lherzolite with variability in composition of slab flux and/or mantle source depletion. The HMBA lavas can be successfully modeled by partial melting of a garnet lherzolite with slab flux compositionally similar to the other lava types, or less likely by partial melting of a spinel lherzolite with a distinctly different, HREE-depleted slab flux.

Papoutsa, Angeliki D.; Pe-Piper, Georgia The relationship between REE-Y-Nb-Th minerals and the evolution of an A-type granite, Wentworth Pluton, Nova Scotia//AMERICAN MINERALOGIST Volume: 98 Issue: 2-3 Pages: 444-462 Published: FEB-MAR 2013

The Wentworth Pluton in the Eastern Cobequid Highlands consists principally of metaluminous to peralkaline A-type granite (similar to 362 Ma), a large part of which was remelted by a major gabbro intrusion (similar to 357 Ma). Magmatic minerals like allanite-(Ce), chevkinite-(Ce), zircon, and hingganite-(Y) and post-magmatic mineral phases, such as REE-bearing epidote, samarskite-(Y), aeschynite-(Y), fersmite, thorite-like phases, and hydroxylbastnasite-(Ce), were identified. The presence of fluorine in the parental magma, indicated by whole-rock geochemical data and the presence of fluorite, increased the solubility of monazite and xenotime and thus facilitated retainment of rare metals in the magmatic system. Fractionation of allanite-(Ce) and chevkinite-(Ce) led to a melt enriched in heavy rare earth elements (HREE), from which hingganite-(Y) crystallized during late magmatic stages. The remelting of the early granite led to fluorine and sulfur release in volatile phases, which circulated with hydrothermal fluids, thus mobilizing the REE and other rare metals. Reduction of fluorine activity during the late to post-solidus crystallization resulted in the precipitation of HREE and rare metals in samarskite-(Y), thereby enriching the residual hydrothermal fluids in light rare earth elements (LREE). Post-magmatic LREE minerals, such as hydroxylbastnasite-(Ce), either replaced earlier minerals or precipitated from these hydrothermal fluids. Carbonate fluids involved in a late regional hydrothermal circulation event along the Cobequid-Chedabucto fault (320-315 Ma) promoted Ti mobility and the formation of TiO2 minerals and probably of aeschynite-(Y). This mineralogical diversity, in addition to the complex geological history of the pluton, provides a unique opportunity to correlate the formation of individual rare-metal minerals to different stages of pluton evolution and thus provide an insight to the formation conditions of these minerals.

Pe-Piper, Georgia; Zhang, Yuanyuan; Piper, David J. W.; et al. Relationship of Mediterranean type lamproites to large shoshonite volcanoes, Miocene of Lesbos, NE Aegean Sea//LITHOS Volume: 184 Pages: 281-299 Published: JAN 2014

Shoshonites, which are high-K trachyandesitic rocks, are found in many orogenic belts and are commonly of post-collisional origin. The petrogenesis of shoshonites has been widely debated. Small lava flows and dykes of lamproite and related lamproitic rocks of early Miocene age in Lesbos are coeval with voluminous shoshonite volcanoes. Their distinctive petrology and isotope geochemistry provide an exceptional opportunity to assess the petrogenetic relationship between lamproites and shoshonites. The lamproitic rocks contain phenocrysts of forsteritic olivine (as high as Fo(93)) and clinopyroxene, both with inclusions of chrome spinel (Cr# similar to 0.9 or similar to 0.6) and carbonate melt inclusions, indicating the presence of carbonatite melts. Some complexly zoned clinopyroxene from lamproitic rocks have salite cores with chemical composition suggesting they formed in the upper mantle in a melt strongly enriched in LILE and LREE. Both lamproites and shoshonites show continuous trends of trace elements and their isotopic compositions overlap. Lack of variation in K with Mg# or SiO2 for particular temporal-spatial groups of shoshonites suggests derivation from particular inhomogeneous mantle rather than fractionation processes. In contrast to other pen-Mediterranean lamproites, the Lesbos lamproites and shoshonites have unusual Pb isotope composition that requires a common origin from subcontinental lithospheric mantle enriched in LILE in the Paleozoic. This enrichment process involved partial melting of subducted carbonate-bearing pelites. Triassic rift-related volcanism and formation of Jurassic small ocean basins produced extreme depletion of parts of the mantle. Lamproitic magma was derived from melting of enriched refractory harzburgite, whereas enriched lherzolite, wehrlite and pyroxenite partially melted to supply larger volumes of shoshonitic and related magmas. The NE Aegean Miocene shoshonite province is thus not directly related to contemporary subduction, but may have been triggered by related back-arc extension. (C) 2013 Elsevier B.V. All rights reserved.


Rift-related Cenozoic alkaline mafic lavas from northern Victoria Land (Antarctica) carry abundant mantle xenoliths whose oxygen fugacities (fO(2)) were determined to assess how the metasomatism, related to Cenozoic magmatism, affected the state of oxidation of the lithospheric mantle. The xenoliths used for this study are anhydrous spinel peridotites sampled in two localities, Greene Point and Baker Rocks, that show different extents of metasomatism: these are limited to incompatible element enrichments in Greene Point and to enrichments in major, minor and trace elements at Baker Rocks. The data set includes a composite xenolith from Baker Rocks, formed by a depleted lherzolite crosscut by an amphibole-bearing vein. Mossbauer spectroscopy was used to accurately determine the Fe3+/Fe-tot ratios in spinel and amphibole minerals. Amphiboles were also characterized by Single-Crystal X-ray Diffraction, and the crystallographic data were used to calculate the dehydrogenation. The oxidation state recorded by the xenoliths ranges from 0.2 to 1.5 log-bar units below the fayalite-magnetite-quartz (FMQ) buffer (Delta logfO(2)) with the highest values observed in the metasomatized samples from Greene Point. For the vein of composite Baker Rocks xenolith, Delta log fO(2) was estimated on the basis of the amphibole in -1.7 log-bar units, a value close to those calculated for all Baker Rocks xenoliths (Delta logfO(2) = -1.5 to -1.1 log-bar units). These results indicate a similar oxidation state for lithospheric mantle prior to the metasomatic event at Greene Point and Baker Rocks (Delta logfO(2) similar to -1.3 log-bar units). Metasomatism produced different effects in the shallow mantle at the two sites. At Greene Point, an oxidizing metasomatic melt caused the rise of fO(2) in peridotite portions close to melt conduits up to FMQ. In contrast, at Baker Rocks, a metasomatizing melt with fO(2) similar to that of the peridotite matrix produced chemical changes in the surrounding mantle rocks and amphibole crystallization without significantly modifying the local oxidation state. The origin of such different metasomatic melts, as well as the variety of primary magmas produced during the magmatic phase of Cenozoic rifting, is linked to the geodynamic evolution of the rift and probably involved the melting of a heterogeneous mantle source composed of a peridotite veined by pyroxene-bearing veins formed from an earlier amagmatic phase of the rift.

Pietruszka, Aaron J.; Norman, Marc D.; Garcia, Michael O.; et al. Chemical heterogeneity in the Hawaiian mantle plume from the alteration and dehydration of recycled oceanic crust//EARTH AND PLANETARY SCIENCE LETTERS Volume: 361 Pages: 298-309 Published: JAN 1 2013

Inter-shield differences in the composition of lavas from Hawaiian volcanoes are generally thought to result from the melting of a heterogeneous mantle source containing variable amounts or types of oceanic crust (sediment, basalt, and/or gabbro) that was recycled into the mantle at an ancient subduction zone. Here we investigate the origin of chemical heterogeneity in the Hawaiian mantle plume by comparing the incompatible trace element abundances of tholeiitic basalts from (1) the three active Hawaiian volcanoes (Kilauea, Mauna Loa, and Loihi) and (2) the extinct Koolau shield (a compositional end member for Hawaiian volcanoes). New model calculations suggest that the mantle sources of Hawaiian volcanoes contain a significant amount of recycled oceanic crust with a factor of similar to 2 increase from similar to 8-16% at Loihi and Kilauea to similar to 15-21% at Mauna Loa and Koolau. We propose that the Hawaiian plume contains a package of recycled oceanic crust (basalt and gabbro, with little or no marine sediment) that was altered by interaction with seawater or hydrothermal fluids prior to being variably dehydrated during subduction. The recycled oceanic crust in the mantle source of Loihi and Kilauea lavas is dominated by the uppermost portion of the residual slab (gabbro-free and strongly dehydrated), whereas the recycled oceanic crust in the mantle source of Mauna Loa and Koolau lavas is dominated by the lowermost portion of the residual slab (gabbro-rich and weakly dehydrated). The present-day distribution of compositional heterogeneities in the Hawaiian plume cannot be described by either a large-scale bilateral asymmetry or radial zonation. Instead, the mantle source of the active Hawaiian volcanoes is probably heterogeneous on a small scale with a NW-SE oriented spatial gradient in the amount, type (i.e., basalt vs. gabbro), and extent of dehydration of the ancient recycled oceanic crust. Published by Elsevier B.V.

Prelevic, Dejan; Jacob, Dorrit E.; Foley, Stephen F. Recycling plus: A new recipe for the formation of Alpine-Himalayan orogenic mantle lithosphere//EARTH AND PLANETARY SCIENCE LETTERS Volume: 362 Pages: 187-197 Published: JAN 15 2013

The origin of the lithospheric mantle beneath accretionary orogens is enigmatic; although severe compression of the buoyant crust occurs, the mantle lithosphere is generally thought to be removed and returned to the convecting mantle. We suggest that during the accretion of oceanic arcs and small continental blocks in the Mediterranean region, and more generally throughout the whole Alpine-Himalayan orogenic belt, the mantle lithosphere is newly created and composed of intimately mixed peridotite and crustal material from the forearc region. Potassium-rich volcanic rocks emplaced sometimes more than 30 Ma after the formation of this lithosphere carry evidence for the presence of extremely depleted peridotite in their sources, but also for mica-bearing pyroxenites formed by reaction between subducted continental sediments and peridotite. Olivines crystallized from the magmas and mantle-xenocrysts derived from the enriched mantle, have elevated concentrations of Li that correlate positively with Sr-87/Sr-86 of the lavas, indicative of an origin from continental crustderived sediments. If much of the continental crust is formed in accretionary orogens of this type, then extensive tracts of the continental lithosphere may contain mixtures of ultradepleted peridotite and recycled crustal material. In this case a portion of the subducted sediment is not returned to the convecting mantle, but becomes stored within the subcontinental lithospheric mantle. (C) 2012 Elsevier B.V. All rights reserved.

Pritchard, Chad J.; Larson, Peter B. Genesis of the post-caldera eastern Upper Basin Member rhyolites, Yellowstone, WY: from volcanic stratigraphy, geochemistry, and radiogenic isotope modeling //CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 164 Issue: 2 Pages: 205-228 Published: AUG 2012

n array of samples from the eastern Upper Basin Member of the Plateau Rhyolite (EUBM) in the Yellowstone Plateau, Wyoming, were collected and analyzed to evaluate styles of deposition, geochemical variation, and plausible sources for low delta O-18 rhyolites. Similar depositional styles and geochemistry suggest that the Tuff of Sulphur Creek and Tuff of Uncle Tom's Trail were both deposited from pyroclastic density currents and are most likely part of the same unit. The middle unit of the EUBM, the Canyon flow, may be composed of multiple flows based on a wide range of Pb isotopic ratios (e.g., Pb-206/Pb-204 ranges from 17.54 to 17.86). The youngest EUBM, the Dunraven Road flow, appears to be a ring fracture dome and contains isotopic ratios and sparse phenocrysts that are similar to extra-caldera rhyolites of the younger Roaring Mountain Member. Petrologic textures, more radiogenic Sr-87/Sr-86 in plagioclase phenocrysts (0.7134-0.7185) than groundmass and whole-rock ratios (0.7099-0.7161), and delta O-18 depletions on the order of 5aEuro degrees found in the Tuff of Sulphur Creek and Canyon flow indicate at least a two-stage petrogenesis involving an initial source rock formed by assimilation and fractional crystallization processes, which cooled and was hydrothermally altered. The source rock was then lowered to melting depth by caldera collapse and remelted and erupted. The presence of a low delta O-18 extra-caldera rhyolite indicates that country rock may have been hydrothermally altered at depth and then assimilated to form the Dunraven Road flow. Times Cited: 3 (from All Databases)

Rao, N. V. Chalapathi; Lehmann, B. Kimberlites, flood basalts and mantle plumes: New insights from the Deccan Large Igneous Province // EARTH-SCIENCE REVIEWS Volume: 107 Issue: 3-4 Pages: 315-324 Published: AUG 2011

A clear-cut temporal and spatial relationship between small-volume, volatile-rich and highly potassic continental melt fractions, such as kimberlites and related rocks, and large-volume continental flood basalts exists in several Large Igneous Provinces (LIPs). Many of these LIPs are also widely regarded as products of mantle plume-lithosphere interactions. The small-volume melts either immediately pre-date or post-date or even are co-eval with the main flood basalt event. The overlap of ages between the flood basalts and the kimberlites very likely reflects a cause and effect relationship via mantle plumes. Recently discovered end-Cretaceous diamondiferous kimberlites (orangeites) in the Bastar craton of central India which are synchronous with the flood basalts, carbonatites, lamprophyres and alkaline rocks of the Deccan LIP provide an opportunity to re-evaluate the role of mantle plume-lithosphere interactions in the generation of these disparate magmas. The geographical zonation of the kimberlite-lamprophyre-carbonatite-alkaline rock spectrum in the Deccan LIP is inferred to reflect variable thickness of the pre-Deccan Indian lithosphere with a thinner lithosphere along the known rift zones of northwestern and western India and a thickened lithosphere underlying the Bastar craton of central India. This heterogeneity is thought to have controlled the volume of melt generation and melt ascent, as well as the ultimate alkaline magma type. These findings are supported by the regional lithospheric thickness map, generated from converting seismic shear wave velocities into temperature profiles, which clearly depicts that the present-day lithosphere beneath the Bastar craton is thicker than that in western and NW India where the centre of the Deccan plume-head was located. Thermal weakening of the sub-Bastar craton due to mantle plume-lithosphere interaction at the end-Cretaceous resulting in a thin-spot is suggested to have controlled the Deccan-related mafic dyke emplacement in the Bastar craton. (C) 2011 Elsevier B.V. All rights reserved.

Rao, N. V. Chalapathi; Lehmann, B.; Mainkar, D.; et al. Petrogenesis of the end-Cretaceous diamondiferous Behradih orangeite pipe: implication for mantle plume-lithosphere interaction in the Bastar craton, Central India//CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 161 Issue: 5 Pages: 721-742 Published: MAY 2011

We present mineral chemistry, geochemistry and Sr and Nd isotope data of drillcore samples from the Late Cretaceous (65 Ma), diamondiferous Behradih ultramafic pipe, Bastar craton, Central India, which is emplaced synchronous with the Deccan flood basalt eruption. The rock is affected by pervasive serpentine-talc-carbonate alteration and consists of pelletal lapilli and variously sized olivine and phlogopite macrocrysts, set in a groundmass of abundant clinopyroxene, chrome spinel, apatite, Fe-rich perovskite (< 50 mu m), zircon, titanite, rutile and calcite. Mineralogical studies identify the Behradih pipe as orangeite (formerly termed as Group II kimberlite) and establish the occurrence of such rocks outside the Kaapvaal craton, southern Africa. As the age of the Behradih orangeite overlaps with that of the main phase of the Deccan flood basalt magmatism, we infer a common tectonomagmatic control vis-a-vis the Deccan-related mantle plume. Trace element ratios and the Nd isotope signatures of the Behradih pipe imply that the Deccan plume has only contributed heat, but not substantial melt, to the Behradih magma with a cause-and-consequence relationship between them. Our study highlights (a) a striking similarity in the genesis of Late Cretaceous orangeites associated with the continental flood basalts in the Kaapvaal and Bastar cratons but related to different mantle plumes and (b) the role of plume-lithosphere interaction in the generation of orangeites.

Ridolfi, Filippo; Renzulli, Alberto Calcic amphiboles in calc-alkaline and alkaline magmas: thermobarometric and chemometric empirical equations valid up to 1,130A degrees C and 2.2 GPa // CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Volume: 163 Issue: 5 Pages: 877-895 Published: MAY 2012

The following article presents constraints of the stability of Mg-rich (Mg/(Mg + Fe2+) > 0.5) calcic amphibole in both calc-alkaline and alkaline magmas, testing of previous thermobarometers, and formulation of new empirical equations that take into consideration a large amount of literature data (e.g. more than one thousand amphibole compositions among experimental and natural crystals). Particular care has been taken in choosing a large number of natural amphiboles and selecting quality experimental data from literature. The final database of experimental data, composed of 61 amphiboles synthesized in the ranges of 800-1,130A degrees C and 130-2,200 MPa, indicates that amphibole crystallization occurs in a horn-like P-T stability field limited by two increasing curves (i.e. the thermal stability and an upper limit), which should start to bend back to higher pressures. Among calcic amphiboles, magnesiohornblendes and tschermakitic pargasites are only found in equilibrium with calc-alkaline melts and crystallize at relatively shallow conditions (P up to similar to 1 GPa). Kaersutite and pargasite are species almost exclusively found in alkaline igneous products, while magnesiohastingsite is equally distributed in calc-alkaline and alkaline rocks. The reliability of previous amphibole applications was checked using the selected experimental database. The results of this testing indicate that none of the previous thermobarometers can be successfully used to estimate the P, T and fO(2) in a wide range of amphibole crystallization conditions. Multivariate least-square analyses of experimental amphibole compositions and physico-chemical parameters allowed us to achieve a new thermobarometric model that gives reasonably low uncertainties (T +/- A 23.5A degrees C, P +/- A 11.5%, H2Omelt +/- 0.78wt%) for calc-alkaline and alkaline magmas in a wide range of P-T conditions (up to 1,130A degrees C and 2,200 MPa) and a dagger NNO values (+/- 0.37 log units) up to 500 MPa. The K-A-Al-[4] relation in amphibole can be readily used to distinguish crystals of calc-alkaline liquids from those of alkaline magmas. In addition, several chemometric equations allowing to estimate the anhydrous composition of the melts in equilibrium with amphiboles of calc-alkaline magmas were derived.

Sharkov, E. V.; Chistyakov, A. V. The Early Paleoproterozoic Monchegorsk Layered Mafite-Ultramafite Massif in the Kola Peninsula: Geology, Petrology, and Ore Potential //PETROLOGY Volume: 20 Issue: 7 Pages: 607-639 Published: DEC 2012

The Early Paleoproterozoic Monchegorsk Complex is exposed over an area of 550 km(2) and comprises two layered mafite-ultramafite intrusions of different age: the Monchegorsk pluton of ultramafic and mafic rocks and the predominantly gabbroid Main Range Massif (also referred to as the Moncha-Chuna-Volch'i Tundras Massif), which are separated by a fault. Both massifs consists of intercalating cumulates (first of all, Ol +/- Crt, Ol + Opx +/- Crt, Opx, Opx + Pl +/- Cpx, and Pl), they were produced by similar melts of siliceous high-Mg series but differ in the stratigraphy of their cumulates: while the Monchegorsk pluton is dominated by ultramafites, the Main Range Massif consists mostly of gabbroids, first of all, of gabbronorites. The complex is accompanied by PGE-Cu-Ni ore mineralization, low-sulfide Pt-Pd mineralization, and chromite mineralization. Judging from geological data and isotopic dates, the Monchegorsk Complex is a long-lived magmatic center, which evolved over a time span of 50 Myr at 2.50-2.46 Ga. The Main Range Massif is younger and likely truncates the western continuation of the Monchegorsk pluton. The complex is spatially restricted to the zone of the Middle Paleoproterozoic regional Central Kola Fault and is now tectonic collage whose rocks were variably affected by overprinted metamorphism in the course of deformations. These processes most significantly affected rocks along the peripheries of the Monchegorsk pluton in the south. These rocks were completely transformed under greenschist-facies conditions but often preserved their primary textures and structures. The processes overprinted both the marginal portions of the pluton itself and the rocks of its second phase, which are accompanied by economic low-sulfide PGE deposits. The PGE-Cu-Ni ore mineralization of the Monchegorsk Complex is genetically related to two distinct evolutionary episodes with a quiescence period in between: (1) The emplacement of large layered mafite-ultramafite intrusions at 2.5-2.45 Ga. Economic deposits of sulfide Cu-Ni ores with subordinate PGE mineralization occur within the Monchegorsk pluton, and the moderate-grade low-sulfide PGE ores are related to its second evolutionary phase (in the foothills of Vuruchuaivench and in the Moroshkovoe Lake, and Southern Sopcha areas). The primary magmatic ore mineralization is predominantly Cu-Fe-Ni sulfide with PGE bismuthides-tellurides. (2) The Monchegorsk Complex was involved in the zone of the Central Kola Fault at 2.0-1.9 Ga and was broken in a collage of tectonic blocks. The rocks were sheared along the boundaries of the blocks and were affected by overprinted metamorphism, which proceeded under greenschist-facies conditions in the structures surrounding the Monchegorsk pluton in the south. Thereby the primary PGE-Cu-Ni ore mineralization underwent metamorphic processes was recrystallized with the formation of Pt-Pd arsenides, stannides, antimonides, selenides, etc. This processes was associated with the partial redistribution of PGE with their local accumulation (up to economic concentrations), and the orebodies themselves acquired diffuse outlines. In other words, the second episode was marked by the transformation of the older primary magmatic ore mineralization. DOI: 10.1134/S0869591112070041

Sheard, Emma R.; Williams-Jones, Anthony E.; Heiligmann, Martin; et al. Controls on the Concentration of Zirconium, Niobium, and the Rare Earth Elements in the Thor Lake Rare Metal Deposit, Northwest Territories, Canada //ECONOMIC GEOLOGY Volume: 107 Issue: 1 Pages: 81-104 Published: JAN-FEB 2012

The Thor Like rare metal (Zr, Nb, REE, Ta, Be, Ca) deposits in Canada's Northwest Territories represent one of the largest resources of zirconium, niobium. and the heavy rare earth elements (FIB E IF,) in the world. Much of the potentially ecolunnic mineralization was concentrated by magmatic processes. However, there is also evidence of autometasomatic processes and remobilization of Zr and REE by liydrot henna! fluids. The deposits are situated at the southern edge of the Slave province of the Canadian Shield, within the 2091 to 2185 Ma alkaline to peralkaline Blachford Like Intrusive Complex. A layered alkaline suite dominated by aegirine nepheline syenite occurs in the center of this suite of rocks and is considered to represent die youngest phase of the complex. Much of the rare metal mineralization occurs in two subhorizontal tabular layers, which form upper and lower zones of the Nechalacho deposit (formerly the Lake zone), and in Zr is hosted primarily be zircon. Nb primarily by ferrocolumbite and fergusonite-(Y), and HREE by fergusonite-(Y) and zircon. The LREE are present mainly in nionazite-(Ce), allanite-(Ce), bastnasite-(Ce), parisite-(Ce), and synchysite-(Ce). Much of the HREE mineralization in the lower mineralized zone occurs in secondary zircon, which forms small (10-30 mu m) anhedral grains in psendomorphs after probable endialyte. In the upper zone, zircon is a magmatic cumulate mineral, which was replaced locally by secdulary BEE-bearing minerals. Element distribution maps of zircon crystals in the tipper zone indicate that the FIBEB were mobilized from the cores and locally precipitated as fergusonite-(Y) along microfractures. The light rare earth elements (LREE) were also mobilized locally from both primary zircon and inferred primary eudialyte. The occurrence of zircon in fractures, wrapped around brecciated K-feldspar fragments, and as a secondary phase in pseudomorphs are evidence of its hydrothermal origin and/or of remobilizatimi of prilflarY zirconnun. A model is proposed in which injection of separate pulses of iniaskitic and agpaitic magma resulted in the crystallization of an upper zone rich in zircon and a lower zone rich in dutiable. Primary euclialyte was later altered in situ to zircon-fergusouite-(Y)-bastniisite-(Ce)-parisite4Ce)-synchysite-(Ce)-allanite-(Ce)-albitequartz-biotite-fluorite-kutualiorite-hematite-bearing pseudomorphs by an inferred illumine-enriched magmatic hydrothernial fluid. Zirconiiim, niobinni, and BEE in both the upper and lower Zones were subsequently mobilized during multiple metasomatic events, which, for the most part, served to further enrich the primary layers in HEE (albitization generally dispersed BEE and high field strength elements (HESE)) and created new secondary H E phases.

Sun, Wei-Dong; Ling, Ming-Xing; Chung, Sun-Lin; et al. Geochemical Constraints on Adakites of Different Origins and Copper Mineralization//JOURNAL OF GEOLOGY Volume: 120 Issue: 1 Pages: 105-120 Published: JAN 2012

The petrogenesis of adakites holds important clues to the formation of the continental crust and copper +/- gold porphyry mineralization. However, it remains highly debated as to whether adakites form by slab melting, by partial melting of the lower continental crust, or by fractional crystallization of normal arc magmas. Here, we show that to form adakitic signature, partial melting of a subducting oceanic slab would require high pressure at depths of >50 km, whereas partial melting of the lower continental crust would require the presence of plagioclase and thus shallower depths and additional water. These two types of adakites can be discriminated using geochemical indexes. Compiled data show that adakites from circum-Pacific regions, which have close affinity to subduction of young hot oceanic plate, can be clearly discriminated from adakites from the Dabie Mountains and the Tibetan Plateau, which have been attributed to partial melting of continental crust, in Sr/Y-versus-La/Yb diagram. Given that oceanic crust has copper concentrations about two times higher than those in the continental crust, whereas the high oxygen fugacity in the subduction environment promotes the release of copper during partial melting, slab melting provides the most efficient mechanism to concentrate copper and gold; slab melts would be more than two times greater in copper (and also gold) concentrations than lower continental crust melts and normal arc magmas. Thus, identification of slab melt adakites is important for predicting exploration targets for copper- and gold-porphyry ore deposits. This explains the close association of ridge subduction with large porphyry copper deposits because ridge subduction is the most favorable place for slab melting.


Growing interest in the mineral perovskite (CaTiO3) as a U-Pb chronometer and archive of near-primary Sr and Nd isotope compositions in magmatic systems highlights the need for well-characterized mineral standards. Based on a conventionally determined, high-precision Sr and Nd isotope data set, we propose perovskite from the alkaline Ice River intrusion as a natural reference material for Sr and Nd isotope ratio determinations. Ice River perovskite has mean present-day Sr-87/Sr-86 (TIMS) and Nd-143/Nd-144 (ID-MC-ICP-MS) ratios of 0.702838 +/- 51 and 0.512581 +/- 32, respectively (2-sigma uncertainties). The TIMS Pb-206/U-238 age of 361.7 +/- 1.0 Ma (2-sigma), determined on the same crystal fragments as the Sr and Nd isotope compositions, falls within the accepted range of 355-372 Ma for the Ice River intrusion. Although there is a similar to 2.2% difference between the ages of Ice River perovskite (similar to 355-363 Ma) reported in various U-Pb studies (determined by TIMS, SIMS, and LA-MC-ICP-MS methods), the material investigated here has the currently best-calibrated U-Pb systematics for perovskite. We therefore recommend the Pb-206/U-238 age of 361.7 +/- 1.0 Ma as a reference value for use in geochronology studies. Perovskite is a prime target for petrogenetic studies of kimberlites and related alkaline rocks, because it preserves primary magmatic signatures. The ability to combine important petrogenetic information with high-resolution U-Pb emplacement ages at mineral scale will be instrumental for an improved understanding of deep magmatism beneath cratons and areas of rifted continental lithosphere. (C) 2012 Elsevier B.V. All rights reserved.

Tappe, Sebastian; Steenfelt, Agnete; Nielsen, Troels Asthenospheric source of Neoproterozoic and Mesozoic kimberlites from the North Atlantic craton, West Greenland: New high-precision U-Pb and Sr-Nd isotope data on perovskite//CHEMICAL GEOLOGY Volume: 320 Pages: 113-127 Published: AUG 6 2012

We present combined U-Pb, Sr, and Nd isotope data for small perovskite crystal fractions from kimberlites in West Greenland. Based on this high-precision TIMS data set, we revise the age range for kimberlite magma emplacement in the Sarfartoq and Tikiusaaq fields to 550-590 Ma and 158-166 Ma, respectively. These improved U-Pb perovskite age constraints reinforce the close temporal association of kimberlite and carbonatite magmatism across the North Atlantic craton. The new combined U-Pb, Sr, and Nd isotope data for perovskites provide evidence for kimberlite magma derivation from a moderately depleted mantle source region during both the Neoproterozoic and Mesozoic. Moreover, we demonstrate that the difference in initial Sr-Nd isotope compositions between the Neoproterozoic Sarfartoq (Sr-87/Sr-86 = 0.70278-0.70293; epsilon(Nd) = + 1.6 to + 3.6; n = 13) and Mesozoic Tikiusaaq (Sr-87/Sr-86 = 0.70319-0.70346; epsilon(Nd) = + 4.8 to + 5.1; n = 3) kimberlite fields can be readily explained by isotopic evolution of a common mantle reservoir. This mantle reservoir appears to have continuously participated in global crust-mantle differentiation and recycling, which points to the well-stirred convective upper mantle as the ultimate kimberlite magma source region beneath West Greenland. The apparent geographic shift of kimberlite and associated carbonatite magmatic activity from the craton margin during the Neoproterozoic toward the craton center during the Mesozoic is explained by changes in localized, small-scale mantle flow along the underside of progressively thinning cratonic lithosphere. (C) 2012 Elsevier B.V. All rights reserved.

Thompson, M. D.; Barr, S. M.; Grunow, A. M. Avalonian perspectives on Neoproterozoic paleogeography: Evidence from Sm-Nd isotope geochemistry and detrital zircon geochronology in SE New England, USA //GEOLOGICAL SOCIETY OF AMERICA BULLETIN Volume: 124 Issue: 3-4 Pages: 517-531 Published: MAR-APR 2012

Arc-related Northern Appalachian Ava-Ionian terranes developed in the ocean surrounding Rodinia beginning around 760 Ma, so paleogeographic constraints on these terranes have implications for the margins of Rodinia itself in Neoproterozoic time. The first Sm-Nd isotopic data together with new detrital zircon ages from SE New England suggest that at least this segment of Avalonia contains rocks with contributions from crustal sources in Baltica, rather than Amazonia as commonly argued. Eight samples from 610 to 600 Ma Dedham, Dedham North, Milford, Fall River, Esmond, and Westwood granites in SE New England yield epsilon(Nd) (600) values from -1.2 to +2.2 and depleted mantle model ages ranging from 2.2 Ga to 1.0 Ga. The younger model ages, reflecting largely juvenile magmatic components, are typical of other Avalonian terranes in Atlantic Canada. The oldest model ages can be produced by mixing juvenile mantle extractions with 10%-15% Baltic crust. The isotopic composition of Baltic crust in these calculations is proxied by Svecofennian metasedimentary rocks with detrital zircon suites comparable to those obtained from younger than 912 Ma quartzite of the Westboro Formation intruded by the Dedham Granite north of Boston (Massachusetts). An Avalonia-Baltica connection is also consistent with available paleomagnetic data placing both areas at moderate south paleolatitude between ca. 615 Ma and ca. 575 Ma during Ediacaran deposition of their respective Squantum-Gaskiers and Varanger glacial deposits.

Vikent'ev, I. V.; Borisova, A. Yu.; Karpukhina, V. S.; et al.Direct data on the ore potential of acid magmas of the Uzel'ginskoe ore field (Southern Urals, Russia) //DOKLADY EARTH SCIENCES Volume: 443 Issue: 1 Pages: 401-405 Published: MAR 2012

Vrevskii, A. B.Age and isotope geochemistry of ore-hosting granodiorites of the Nyal'm-1 gold deposit (Kolmozero-Voron'ya greenstone belt, Kola Peninsula) //DOKLADY EARTH SCIENCES Volume: 442 Issue: 1 Pages: 100-104 Published: JAN 2012


This paper reports on a rare magmatic suite of adakitic rocks and associated magnesian and potassium-rich magmatic enclaves and dikes, which occur in the Tunchang-Fengmu area, Hainan Island (Southeast China). LA-ICP-MS zircon U-Pb age data show that they were generated in the late Early Cretaceous (similar to 107 Ma). The adakitic rocks, consisting mainly of granodiorites and biotite granites, are high-K cal-calkaline and have low Mg-# values (0.27-0.50). They are geochemically similar to slab-derived adakites, e.g., with high SiO2, Al2O3, Sr, Sr/Y and La/Yb values, low Y and Yb contents, and negligible Eu and positive Sr anomalies. They also have relatively uniform (Sr-87/Sr-86); (0.7086-0.7096), (Pb-206/Pb-204)(i) (18.50-18.61), (Pb-207/Pb-204)(i) (15.56-15.64) and (Pb-208/Pb-204)(i) (38.17-38.44) isotope ratios, with slightly variable epsilon(Nd)(t) (-3.85 to -6.55) and zircon in situ epsilon(Hf)(t) (-4.7 to +1.7) values. The mafic enclaves and dikes display disequilibrium textures (e.g., multiple-zoned clinopyroxene with low-MgO rims in contact with perthite and quartz microcrystals). They are high-K calc-alkaline and shoshonitic, and all but one sample have high Mg-# (0.63-0.72) values. These mafic rocks are characterized by light rare earth element enrichment and heavy rare earth element (REE) depletion, negligible Eu and Sr and positive Pb anomalies, and Nb and Ta depletion. They have slightly more variable initial Sr-87/Sr-86 isotope ratios (0.7064-0.7086), epsilon(Nd)(t) (-5.1 to +0.1) values. and (Pb-206/Pb-204)(i) (18.35-18.50), (Pb-207/Pb-204)(i) (15.45-15.59) and (Pb-208/Pb-204)(i) (38.18-38.70) ratios. One mafic dike sample has zircon in situ epsilon(Hf)(t) values (-4.94 to -2.42) similar to those of adakitic rocks (-4.7 to +1.7) in the area. We suggest that the adakitic rocks were most likely generated by partial melting of newly underplated basaltic lower crust with arc-like geochemical characteristics, and the primitive compositions of the mafic enclaves and dikes likely originated from lithospheric + asthenospheric mantle sources meta-somatized by subducted oceanic sediments or a relatively juvenile lithospheric mantle source. Mantle-derived primitive magmas likely underwent mixing at depth with minor crustally-derived felsic magmas before being injected into the adakitic magma chamber. Such injections may have broken up the magma into discrete globules and convective motion distributed the enclaves through the adakitic host. Asthenosphere upwelling due to the roll-back of the subducted Paleo-Pacific plate likely triggered the coeval late Early Cretaceous crust- and mantle-derived magmatism, resulting in the magma hybridization observed on Hainan Island. (C) 2012 Elsevier B.V. All rights reserved.

Wang, Jiasheng; Wen, Hanjie; Fan, Haifeng; et al.Sm-Nd geochronology, REE geochemistry and C and O isotope characteristics of calcites and stibnites from the Banian antimony deposit, Guizhou Province, China //GEOCHEMICAL JOURNAL Volume: 46 Issue: 5 Pages: 393-407 Published: 2012

The Banian sediment-hosted antimony deposit is a medium-sized deposit located in the Dushan County, South Guizhou, China. Calcite is the dominant gangue mineral and can be divided into two types: white and pink. Pink calcite is intimately associated with mineralization. Sm-Nd dating of five white calcites yield an isochron age of 128.2 +/- 3.2 Ma, with initial epsilon(Nd) = -4.3 and MSWD = 0.54, while six pink calcites yield an identical age of 126.4 +/- 2.7 Ma with initial epsilon(Nd) = -6.0 and MSWD = 0.68. These new age constraints suggest that the Banian deposit formed during the late Yanshanian. Negative initial epsilon(Nd) values. C (-0.5 to -1.8), 0 (12.5 to 14.6) isotopic characteristics of calcites, and field observations of abundance of vuggy open spaces, all suggest significant interaction between fluid and wall rocks. Calcites are characterized by strongly LREE-depleted and MREE- and HREE-enriched (LREE/HREE = 0.11-0.61). Stibnites are LREE-enriched, and MREE- and HREE-depleted (LREE/HREE = 105-500). Wall rocks are characterized by moderate LREE-enriched (LREE/HREE = 6.2-12). Pink calcites are more enriched in LREE (LREE/HREE = 0.11-0.61) than white calcites (LREE/HREE = 0.11-0.23), while the concentration of HREE remains nearly constant in both. The high contents of Fe and Mn in calcites and the negative correlation between Fe+Mn (ppm) and LREE/HREE ratios suggest that the Fe-Mn impurities in calcites may dominate the enrichment of MREE and HREE in calcites from the Banian deposit.

Yan, Xi-An; Liu, Jia-Jun; Han, Si-Yu; et al. Isotope geochemistry and its implications in the origin of Yangla copper deposit, western Yunnan, China //GEOCHEMICAL JOURNAL Volume: 48 Issue: 1 Pages: 19-28 Published: 2014

The Yang la copper deposit is located in western Yunnan Province, China, with an estimated Cu reserve of approximately 1.2 million tons. It is a typical giant copper deposit, and its mining started only recently. The delta C-13(V-PDB) values of the calcites studied vary from -5.1 parts per thousand to 1.0 parts per thousand, implying that the hydrothermal fluids from which the calcites precipitated were derived from the granitic magma. The delta O-18(SMOW(H2O)) and delta D-SMOW values of quartz fluid inclusions range from 0.11 parts per thousand to 2.50 parts per thousand and from -120 parts per thousand to -100 parts per thousand, respectively. These data may suggest the following: (1) mixing between meteoric and magmatic fluids, or (2) the evolution of meteoric fluid by its interaction with igneous or metamorphic rocks. The delta S-34 values of sulfides range from -4.20 parts per thousand to 1.85 parts per thousand (average: -0.85 parts per thousand), which is consistent with the magmatic origin. Based on the He-3/He-4 ratios of fluid inclusions trapped in sulfides of the deposit (0.14-0.17 Ra) and Ar-40/Ar-36 ratios of 301-1053, it can be inferred that the ore-forming fluids of the deposit were derived primarily from the crust with a minor mantle component during the metallogenic processes. Based on C, H, O, and S isotopic compositions, and the Yangla copper deposit is bordered primarily by gently dipping thrust faults near the Linong granodiorite. Moreover, the Re-187-Os-187 isochron age of molybdenite puts the time of metallogenesis at 233.3 +/- 3 Ma, which is virtually coeval with the emplacement of the Linong granodiorite (235.6-234.1 Ma) and highlights the genetic link between the Yangla copper deposit and the Linong granodiorite. It is likely that the ore-forming fluids exsolved from the Linong granodiorite, which was formed by crustal melting induced by the intrusion of mantle-derived magma. During the late Early Permian, the Jinshajiang oceanic plate was subducted to the west, resulting in the formation of a series of gently dipping thrust faults in the Jinshajiang tectonic belt. Subsequently, the thrust faults was tensional during the early Late Triassic, which was a time of transition from collision-related compression to extension in the Jinshajiang tectonic belt; such conditions produced an environment favorable for the formation of ore fluids. This extension, in turn, induced the upwelling of hot asthenosphere, triggering intense melting in the lithospheric mantle and producing voluminous basaltic magma. Subsequently, the mantle-derived magma likely ascended along the fractures and faults to underplate the lower crust, which underwent partial melting to generate voluminous granitic magma. After the magma reached the base of the early-stage Yangla granodiorite, the platy granodiorite at the base of the Yangla body shielded the late-stage magma. Then, this magma cooled slowly, releasing some of its ore-forming fluids into the gently dipping thrust faults near the Yangla granodiorite and producing mineralization.


New laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon ages and geochemical data are reported for the Karamay ophiolitic melange in the West Junggar area at the southwestern margin of the Altaids (or Central Asian orogenic belt), northwestern China. The data were used to identify the petrogenesis of the melange, and to evaluate its tectonic significance. In addition, this study aimed to assess the possible presence of Devonian mantle plume in the region. The Karamay ophiolitic melange crops out at the boundary of the Junggar Basin but is partly hidden by Meso zoic sediments, with an exposure area of similar to 40 km(2). The site contains ultramafic rocks, cumulates, gabbros, pillow lavas, abyssal radiolarian cherts, turbidites, and tuffs, which show typical block-in-matrix structures. Zircon U-Pb analyses from the basalt and gabbro by LA-ICP-MS yielded weighted mean ages of 395 +/- 3 Ma and 387 +/- 8 Ma, respectively. These ages suggest a Middle Devonian emplacement. All basalts bear the signature of ocean-island basalt (OIB) and are characterized by alkaline compositions with high concentrations of Na2O + K2O (3.7-8.5 wt%) and TiO2 (1.5-3.1 wt%); large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion; very weak or no Eu anomalies (Eu/Eu* = 0.9-1.0); and no obvious Nb, Ta, or Ti negative anomalies. We propose that these basaltic rocks were derived from mantle plume-related magmatism associated with the evolution of the Paleoasian oceanic system. The enriched mantle source could have contained 2%-5% garnet and similar to 3% spinel. The rocks also display strong geochemical similarities with the Xigaze seamount basalts, which formed in intra-oceanic settings. Compared to the basalts, the gabbros display mid-ocean-ridge-basalt-type tholeiitic basalt features, derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction-zone environment. These observations are supported by previous work, and they indicate Devonian mantle plume-related magmatism within the Paleoasian Ocean. However, as these rocks are mainly parts of accretionary complexes, whether the Karamay and Darbut ophiolitic melange formed in a single belt remains equivocal, and further work is required to resolve this issue. Thus, there was a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous before final amalgamation and docking to the northern Siberian block.

Yang, Jin-Hui; Sun, Jin-Feng; Zhang, Min; et al. Petro genesis of silica-saturated and silica-undersaturated syenites in the northern North China Craton related to post-collisional and intraplate extension// CHEMICAL GEOLOGY Volume: 328 Special Issue: SI Pages: 149-167 Published: OCT 18 2012

Whole-rock major and trace element and Sr-, Nd- and Hf-isotope data, together with zircon U-Pb and Hf-isotope data, are reported for three alkaline intrusions (Liangjia, Jianfang and Hekanzi) in the Yanshan Fold and Thrust Belt in the northeastern North China Craton, in order to investigate their sources, petrogenesis and tectonic implications. The Liangjia and Jianfang plutons are mainly composed of medium-grained quartz syenites, whereas, the Hekanzi complex consists of nepheline-bearing pyroxene-biotite syenites. Zircon U-Pb dating gives emplacement ages of 254-246 Ma for the Liangjia and Jianfang silica-saturated syenites and 226224 Ma for the Hekanzi silica-undersaturated syenites. The Late Permian silica-saturated alkaline rocks have high silica contents (SiO2 = 69.2-75.7 wt.%) and low MgO (0.04-0.47 wt.%) concentrations, and are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) but with negative Eu, Ba and Sr anomalies and depletion in high field strength elements (HFSEs), with significant negative Nb, Ta, P and Ti anomalies. Geochemical data and Sr-, Nd and Hf-isotopic compositions indicate that they were mainly derived from partial melting of lower crustal materials with extensive pyroxene and plagioclase fractionation. The Triassic silica-undersaturated syenites have relatively high MgO abundances (up to 5.3 wt.%) at basic to intermediate silica contents. They are enriched in LREE and LILE and depleted in HREE and HFSE, with negative Nb. Ta and Ti anomalies. They have relatively low initial Sr-87/Sr-86 ratios and relatively negative whole rock epsilon(Nd)(t) and epsilon(Hf)(t) values and zircon epsilon(Hf)(t) values. All these geochemical features indicate that they were the result of crustal assimilation and fractional crystallization of a mafic magma derived from an amphibole-clinopyroxene-rich lithospheric mantle via small degree partial melting. Based on the regional geology, the Late Permian syenites would form in a post-collisional extension setting, whereas, the Triassic syenites were most likely generated in an intraplate extensional setting, providing time constraints on the geodynamic transition from post-orogenic to intra-plate extension. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Yang, T. N.; Zhang, H. R.; Liu, Y. X.; et al. Permo-Triassic arc magmatism in central Tibet: Evidence from zircon U-Pb geochronology, Hf isotopes, rare earth elements, and bulk geochemistry //CHEMICAL GEOLOGY Volume: 284 Issue: 3-4 Pages: 270-282 Published: MAY 24 2011

There is hot debate on whether there is a Paleo-Tethyan suture within Qiangtang and on how the suture extends in central Tibet. In situ Hf and U-Pb isotopes, and rare earth element (REE) analyses of zircons, together with bulk chemistry, have helped us identify a significant, and previously unknown stage of subduction-related magmatism along the southern part of the eastern Qiangtang block, north of the Shuanghu suture, central Tibet. SHRIMP and LA-ICP-MS zircon U-Pb data demonstrate that the magmatism started as early as 275 Ma, lasted until 248 Ma, and took place at the same time as blueschist and eclogite were forming in the central Qiangtang high- to ultrahigh-pressure metamorphic belt (QMB). The positive epsilon(Hf)(t) values of the magmatic zircons range from 9.71 to 16.73. and indicate derivation of magma from a relatively uncontaminated, depleted mantle. Variations in epsilon(Hf)(t) values and the REE patterns of magmatic zircons, combined with substantial heterogeneities in the whole-rock chemistry, suggest that the arc-related magmatism occurred in pulses, and was long-lived. The present data can be interpreted in terms of a history of progressive subduction during the Early Permian and Early Triassic, during which time continental fragments of EQ affinity were tectonically eroded and subducted into the mantle, along with the subducted oceanic slab. The temporal and spatial correlations between the arc-like volcanic belt and the high-pressure metamorphic belt suggest a Late Paleozoic ocean (Paleo-Tethys) existed between the western and eastern Qiangtang blocks, and that the ocean was closed by northwards subduction. (C) 2011 Elsevier B.V. All rights reserved.

Zhang, Dongyang; Zhang, Zhaochong; Santosh, M.; et al. Perovskite and baddeleyite from kimberlitic intrusions in the Tarim large igneous province signal the onset of an end-Carboniferous mantle plume//EARTH AND PLANETARY SCIENCE LETTERS Volume: 361 Pages: 238-248 Published: JAN 1 2013

Several tens of kimberlitic pipes and dykes are exposed in the Wajilitag area in the western Tarim large igneous province. Here we report for the first time secondary ion mass spectrometric U-Pb age data on perovskite and baddeleyite grains in a kimberlitic pipe and a kimberlitic dyke from the Tarim Craton. The perovskite yielded a well-defined intercept age of 299.8 +/- 4.3 Ma, which is consistent with its corresponding concordia and Pb-206/U-238 ages, corrected for the common Pb contribution, of about 300 Ma. The baddeleyite separated from two kimberlitic samples from a dyke display identical concordia U-Pb ages of 300.8 +/- 4.7 Ma and 300.5 +/- 4.4 Ma. Our age data show that the kimberlitic intrusions were emplaced at ca. 300 Ma, rather than in the late Permian as previously regarded. These new ages are slightly older than the eruption ages of Tarim flood basalts (291-273 Ma), offering a critical regional time marker for the onset of Permo-Carboniferous magmatism in the Tarim Craton. Detailed petrographic observations did not reveal any ultrahigh pressure mineral assemblage in the Wajilitag kimberlitic intrusions. Phlogopites from these intrusions show epsilon(Nd)(t) values of +3.7 to +4.2. The baddeleyites which are texturally primary and therefore inferred to have crystallized directly from the kimberlitic magma, yield a range of epsilon(Hf)(t) from +4.8 to +8.7. These results combined with previously reported geochemical data, suggest that the Wajilitag kimberlitic intrusions were most likely derived from a moderately refractory and depleted subcontinental lithosphere mantle, metasomatized by subduction components associated with an early-middle Paleozoic convergent regime. The kimberlitic magma was generated by small-degree partial melting of the lithospheric mantle in response to the impingement of the Tarim mantle plume. Thus, our new geochronological data suggest the arrival of the mantle plume beneath the Tarim lithosphere at least 10 million years before the onset of Tarim flood basalt volcanism. The end-Carboniferous Wajilitag kimberlitic intrusions, the oldest known phase associated with Carboniferous magmatism in the Tarim Craton, signals the initial magmatic pulse triggered by mantle plume impingement. (C) 2012 Elsevier B.V. All rights reserved.


A combined study of zircon U-Pb ages, Lu-Hf isotopes, mineral 0 isotopes, whole-rock elements and Sr-Nd isotopes was carried out for alkaline intrusive rocks (including gabbro, syenite and granite) in the Sulu orogen. The results provide insights into crust-mantle interaction in the continental subduction zone. SIMS and LA-ICPMS zircon U-Pb dating yield Late Triassic ages of 201 +/- 2 to 212 +/- 1 Ma for their crystallization. These ages are younger than Middle Triassic ages for ultrahigh-pressure (UHP) metamorphism of country rocks, corresponding to syn-exhumation magmatism during continental collision. The alkaline rocks are characterized by the arc-like patterns of trace element distribution, with relative enrichment of LILE and LREE but relative depletion of HFSE. They have high initial Sr-87/Sr-86 ratios of 0.7064 to 0.7114 and highly negative epsilon(Nd)(t) values of -16.4 to -13.8 with two-stage Nd model ages of 2.11 to 2.33 Ga for whole-rock. Zircon Lu-Hf isotope analyses also show highly negative epsilon(Hf)(t) values of -20.9 +/- 0.5 to -14.1 +/- 0.9, with two-stage Hf model ages of 2.10 +/- 0.06 to 2.56 +/- 0.03 Ga. The zircon exhibits relatively consistent delta O-18 values of 5.6 to 6.2 parts per thousand, slightly higher than normal mantle values. The enrichment of radiogenic Sr-Nd-Hf isotopes in the gabbro indicates its origination from an isotopically enriched mantle source, whereas the arc-like pattern of trace element distribution for it suggests a fertile mantle source with enrichment of LILE and LREE. Thus, it is part of the orogenic lithospheric mantle that would be generated by underplate reaction of the subcontinental lithospheric mantle with hydrous felsic melts derived from the subducted continental crust during the Triassic continental collision. On the other hand, there are general similarities in trace element and radiogenic isotope characteristics between the syenite-granite and UHP metaigneous rocks in the Dabie-Sulu orogenic belt, suggesting its genetic link to the subducted continental crust itself. Therefore, the alkaline rocks are derived from partial melting of the orogenic lithospheric mantle and the subducted continental crust in the stage of exhumation. They provide a petrological record of recycling the subducted continental crust into mantle depths with consequent crust-mantle interaction during the continental collision. (C) 2011 Elsevier B.V. All rights reserved.


Ранее в Южной Гоби Монголии были открыты пояс массивов щелочных гранитов и карбонатитовая провинция. Лугингольский массив псевдолейцитовых сиенитов с карбонатитами входил в щелочно-гранитный пояс. Полученные новые цифры возраста показали, что он на 40 млн лет моложе Хан-Богдинского массива и отделен от щелочно-гранитного пояса крупным разломом. На этом же участке Южной Гоби кроме Лугингольского массива с западной стороны от массива в районе горы Барун-Хасар-Ула В.И. Коваленко обнаружены серия даек щелочных К-шонкинитов с жилой редкометалльного карбонатита, а на северо-востоке от Лугингольского массива нами — серия даек щелочных и нефелиновых сиенитов. Эти данные дают основание выделить интрузивный комплекс К-щелочных пород шонкинитов и лейцитовых сиенитов с TR-рудоносными карбонатитами верхнепалеозойского возраста. Таким образом, в Южной Гоби выделяются три разновозрастных комплекса щелочных пород. В статье приводятся уточненные геологические карты трех комплексов. Массивы всех трех комплексов являются месторождениями редких элементов (TR, Nb, Zr, Y и P). Детально рассмотрен химический состав силикатных пород комплекса, редкометалльных агпаитовых пегматитов, карбонатитовых и апатитовых редкометалльных руд. На основе идентичности химического, минерального и геохимического редкометалльного составов шонкинитов Барун-Хасар-Ула и Маунтин Пасс (США) и их карбонатитов вместе с карбонатитами Лугингольского массива делается вывод о их принадлежности к единому формационному комплексу К-щелочных пород и карбонатитов. С использованием графиков спектров TR и спайдеровских диаграмм показана общность и различия редкометалльных пород трех комплексов, а также отличия парагенезисов их редкометалльных минералов. Описывается редкий процесс аморфизации редкометалльных минералов, связанный с высокими температурами их кристаллизации в химической обстановке аномальной кремнекислотности в пегматитах Хан-Богдинского массива. Источником первичных магм щелочно-карбонатитовых комплексов является контаминированная мантия ЕМ-2, прошедшая процесс рециклинга, а для агпаитовых щелочных гранитов Хан-Богдо — деплетированная мантия.


Ареал распространения малых интрузий комплекса эдельвейс щелочных пород и карбонатитов ограничен отрогами Северо-Чуйского хребта на юго-востоке Горного Алтая. По изотопным Ar-Ar данным, его становление происходило в среднем кембрии ~ 507 млн лет назад. Все производные комплекса в последовательности: щелочной клинопироксенит -меланогаббро - щелочной сиенит + кальциокарбонатит представлены в составе только одного массива. Силикатные магматические образования по кремнекислотности и щелочности соответствуют формации калиевых щелочных и субщелочных основных пород. Апатит-флогопитовые Са-карбонатиты обогащены P2O5 (до 3.6 мас. %), Sr (~ 2500-5500 г/т), REE (до ~ 2000 г/т) и, предположительно, имеют ликвационный генезис. Доминирующим магматическим источником комплекса (?Nb(Т) = +6.56…+6.85) послужил плюмовый компонент PREMA-типа. По изотопным данным (87Sr/86Sr(Т) ~ 0.7032-0.7039; ?18О ~ 7.5-14.9 ‰; ?13С ~ -2.7…-8.4 ‰), фракционирование расплавов сопровождалось их коровой контаминацией. Особенности редкоэлементного состава пород свидетельствуют о возможном становлении комплекса в окраинно-континентальной обстановке на фоне развития позднеколлизионного рифтинга и смешения материала умеренно деплетированной (PREMA) и обогащенной надсубдукционной литосферной мантии (EM I или EM II) с веществом континентальной коры. Предполагается, что комплексы щелочных пород и карбонатитов западного сегмента Центрально-Азиатского складчатого пояса имеют первичную плюмовую природу и совместно с другими разноформационными производными раннепалеозойского (510-470 млн лет) магматизма образуют в его пределах крупную изверженную провинцию.

Вялов В.И., Панова Е.Г., Семенов Е.В., Гамов М.И., Попов Ю.В., Ключарев Д.С. РЕДКОЗЕМЕЛЬНЫЕ МЕТАЛЛЫ В ДИКТИОНЕМОВЫХ СЛАНЦАХ И ОБОЛОВЫХ ПЕСЧАНИКАХ ПРИБАЛТИЙСКОГО БАССЕЙНА//Руды и металлы. 2014. № 1. С. 30-35.

Исследованы составы оболовых песчаников (фосфоритов) и диктионемовых сланцев Прибал- тийского осадочного бассейна. В них определены повышенные содержания редкоземельных металлов, достигающие в фосфоритах в сумме с Y минимально-промышленного уровня. Основ- ным источником металлов в оболовых песчаниках служит фосфоритизированный детрит раковин Obolus. В диктионемовых сланцах редкоземельные металлы содержатся в карбонат- фтор-апатите обломков раковин, в мелких кристаллах апатита. Оболовые песчаники могут рассматриваться как новый генетический тип промышленного оруденения на редкоземельные металлы.

Когарко Л.Н. РУДНЫЙ ПОТЕНЦИАЛ ЩЕЛОЧНЫХ МАГМ//Разведка и охрана недр. 2011. № 6. С. 60-64.

Среди магматических формаций мира щелочные породы, включая карбонатиты, обладают самым высоким рудным потенциалом на редкометальное сырье. Исследования показали, что рудоносными зонами на редкометальное сырье Ловозерской интрузии являются только те, которые содержат ранний идиоморфный лопарит и эвдиалит. Необходимым условием появления магматических редкометальных месторождений кумулятивного типа является ранняя котектическая насыщенность расплава в отношении рудного минерала.

Кузнецова Л.Г., Спиридонов А.М., Дриль С.И., Куликова З.И. ГЕОХИМИЯ ЛЕПИДОЛИТОВЫХ ГРАНИТОИДОВ ПРОЯВЛЕНИЯ МУНГУТИЙН ЦАГААН ДУРУЛЖ (ЦЕНТРАЛЬНАЯ МОНГОЛИЯ)//Геология и геофизика. 2012. Т. 53. № 10. С. 1401-1416.

Изучено геолого-геодинамическое положение, петрологические и геохимические особенности жильных лепидолитовых гранитоидов участка Мунгутийн Цагаан Дурулж (МЦД), обнаруженных в Центральной Монголии, в пределах ареала проявления внутриплитного редкометалльного магматизма мезозойского возраста. Установлено, что их обогащение редкими элементами вызвано интенсивным воздействием на лейкограниты с первично слабой редкометалльной минерализацией высокофтористых, богатых K, Li, Rb, Cs, Sn, Be, W флюидов, поступавших из залегавшего на глубине магматического очага редкометалльных гранитных расплавов. Очень высокий уровень содержаний фтора, редких щелочных элементов и Sn, Be, W, типичный для гранитоидов МЦД, сопоставим только с грейзенами редкометалльных гранитов и топаз-лепидолит-альбитовыми пегматитами. Различия с грейзенами могут быть обусловлены в каждом конкретном случае особенностями исходных пород, подвергшихся грейзенизации. Различия грейзенизированных лейкогранитов МЦД с топаз-лепидолит-альбитовыми пегматитами более кардинальные - помимо ярко выраженных петрографических признаков к ним относятся: эволюционный тренд, направленный в сторону снижения содержаний нормативного альбита и не характерный для магматических пород Li-F геохимического типа; катаклаз и разгнейсование пород явно способствовали их химическому преобразованию в данном направлении; стабильно пониженные содержания Nb и Ta - редких элементов, обычно накапливающихся в ходе кристаллизационного фракционирования F-Li гранитных расплавов и слаборастворимых в магматических флюидах. Грейзенизированные гранитоиды МЦД не только сами являются богатыми редкометалльными рудами Li, Rb, F, Sn, но с большой долей вероятности служат признаком присутствия на глубине невскрытого массива редкометалльных гранитов.


В статье систематизированы и обобщены результаты выполненных за последние два десятилетия геологических, геохронологических изотопных и геохимических исследований магматических пород Улкан-Джугджурской анортозит-рапакивигранит-щелочногранитной магматической ассоциации и связанного с ней оруденения. Установлено, что рассматриваемая ассоциация представляет собой типичный пример образований анорогенного типа, формирование которых происходило во внутриплитной геодинамической обстановке и было, вероятнее всего, обусловлено деятельностью мантийного суперплюма. Активность этого суперплюма проявилась на территории Сибирского кратона в возрастном интервале 1.751.70 млрд лет. Формирование этой ассоциации происходило в дискретном режиме, что, вероятнее всего, отражает пульсационную эволюцию сублитосферного мантийного источника. Выделяются два этапа: предрифтовый (17361727 млн лет) и собственно рифтовый (17221705 млн лет) и несколько стадий. Все магматические породы, входящие в состав ассоциации, имеют смешанное мантийно-коровое происхождение. Основные породы были образованы из базальтовой магмы типа OIB, претерпевшей разноглубинную коровую контаминацию. Породы кислого состава формировались в результате смешения различных магм мантийного и корового происхождения. Роль мантийного компонента последовательно увеличивалась в возрастном ряду: умереннощелочной субсольвусный гранит - умереннощелочной гиперсольвусный гранит -щелочной гиперсольвусный гранит. Все эндогенные месторождения района связаны с единым источником мантийным плюмом и его производными. Образование Fe-Ti-апатитовых месторождений в анортозитах происходило в результате интенсивной нижнекоровой контаминации базальтовой магмы вблизи границы М и двух этапов фракционной кристаллизации на различных уровнях глубинности нижне- и верхнекоровом. Редкометальные месторождения района генетически связаны со щелочными гранитами. Формирование урановых месторождений, вероятнее всего, обусловлено процессами среднерифейской реювенации региона и пород Улкан-Джугджурской ассоциации.

Мельникова В.И., Гилева Н.А., Радзиминович Н.А., Масальский О.К., Чечельницкий В.В. СЕЙСМИЧНОСТЬ БАЙКАЛЬСКОЙ РИФТОВОЙ ЗОНЫ ЗА ПЕРИОД ЦИФРОВОЙ РЕГИСТРАЦИИ ЗЕМЛЕТРЯСЕНИЙ (2001-2006 ГГ.)//Вопросы инженерной сейсмологии. 2009. Т. 36. № 1. С. 40-55

Рассматриваются особенности сейсмического режима Байкальской рифтовой зоны в периоды аналоговой (1960-2000 гг.) и цифровой (2001-2006 гг.) регистрации землетрясений. Установлено, что общее количество сейсмических событий, зарегистрированных цифровой аппаратурой, по сравнению с аналоговым периодом наблюдений увеличилось вдвое, а уровень представительности понизился до КР = 7Изучены фокальные механизмы 110 землетрясений с КР ? 8.0. Определено, что подавляющее большинство сейсмических источников в 2001-2006 гг. характеризуется сбросовыми или сдвиго-сбросовыми подвижками. Особое внимание уделено изучению сильных землетрясений (КР ? 13.5; МPSP ? 4.7), механизмы которых отражают региональное поле тектонических напряжений.

Огородников В.Н., Поленов Ю.А., Савичев А.Н. РЕДКИЕ МЕТАЛЛЫ И РЕДКОЗЕМЕЛЬНЫЕ ЭЛЕМЕНТЫ В КИАНИТОВЫХ РУДАХ КОЛЬСКОГО ПОЛУОСТРОВА И УРАЛА//Труды Института геологии и геохимии им. академика А.Н. Заварицкого. 2013. № 160. С. 274-281.


На примере щелочных и субщелочных массивов Енисейского кряжа показаны условия образования и эволюции щелочного и ассоциирующего с ним магматизма в западном обрамлении Сибирского кратона. Приведены петрографические, минералогические, геохимические и геохронологические данные для пород Среднетатарского и Ягодкинского массивов, локализующихся в пределах Татарско-Ишимбинской сутурной зоны. Железистые, метаалюминиевые разности, обогащенные редкими элементами (Nb, Ta, Zr, Hf, РЗЭ), составляющие большинство исследуемых пород, образовывались на этапах фракционной кристаллизации щелочной магмы в обстановке активной континентальной окраины на западе Сибирского кратона в поздненеопротерозойское время — 690—710 млн лет назад. Эти породы ассоциируют с обогащенными Nb породами — лейкогранитами А -типа и карбонатитами. Sm/Nd и Rb/Sr изотопные данные позволяют предполагать доминирование мантийной компоненты в магматических источниках основных и средних пород, и процессы контаминирования этой магмой разных объемов континентального корового материала.

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