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1
Palacz, Z. A., and S. R. Tait. "Isotopic and geochemical investigation of unit 10 from the Eastern Layered Series of the Rhum Intrusion, Northwest Scotland." Geological Magazine 122, no. 5 (1985): 485–90. http://dx.doi.org/10.1017/s0016756800035408.
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AbstractSr and Nd isotopic compositions together with whole rock Sr and Nd abundances and olivine compositions are presented for cumulates from unit 10 of the Eastern Layered Series of the Rhum intrusion, Northwest Scotland.The results show an Nd–Sr isotopic correlation consistent with contamination by high 87Sr/86Sr, low 143Nd/144Nd crust. There is a strong correlation between the degree of contamination, Sr and Nd whole rock abundance and Fe enrichment in cumulus olivine. The allivalites are the most contaminated, while the basal peridotites are uncontaminated. This suggests that the cumulates crystallized from a primitive uncontaminated magma and the allivalites from an evolved contaminated magma. Subsequently, movement of contaminated feldspathic intercumulus liquid has perturbed the isotopic, trace element and olivine composition of the upper peridotites.
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YOSHIKAWA, Masako. "Sr-Nd isotopic compositions of oceanic mantle." Japanese Magazine of Mineralogical and Petrological Sciences 42, no. 6 (2013): 247–57. http://dx.doi.org/10.2465/gkk.120608a.
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Dempsey, C. S., A. N. Halliday, and I. G. Meighan. "Combined Sm-Nd and Rb-Sr isotope systematics in the Donegal granitoids and their petrogenetic implications." Geological Magazine 127, no. 1 (1990): 75–80. http://dx.doi.org/10.1017/s0016756800014175.
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AbstractThe metaluminous to peraluminous granitoids of the Donegal batholith, northwest Ireland, were emplaced at c. 400 Ma into greenschist-amphibolite facies metasediments of the Dalradian Supergroup. Sm-Nd and Rb-Sr isotopic data are provided for eleven granitoid samples from six of the plutons and one specimen from the northeast granodiorite pluton of the Newry complex, Co. Down; the Donegal results reveal essentially similar initial Sr isotope ratios (0.7051–0.7068) but highly variable initial eNd values, −1.2 to −8.3 (and −0.5 for Newry). Certain granitoids have distinctive Nd isotopic compositions characteristic of the involvement of old, LREE-enriched continental crust in some cases or young crust and/or mantle-derived magmas in others. The Nd and Sr isotopic variations can be explained by a variety of mixing hypotheses.
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Roulleau, Emilie, and Ross Stevenson. "Geochemical and isotopic (Nd–Sr–Hf–Pb) evidence for a lithospheric mantle source in the formation of the alkaline Monteregian Province (Quebec)." Canadian Journal of Earth Sciences 50, no. 6 (2013): 650–66. http://dx.doi.org/10.1139/cjes-2012-0145.
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We present new major element and isotopic (Nd–Sr–Hf–Pb) data and modelling from alkaline rocks of the Monteregian Igneous Province of southern Quebec (Canada) that constrain the mantle source and the magmatic origin of these rocks. The whole-rock chemical composition of the intrusions is consistent with fractional crystallization of an assemblage of olivine ± clinopyroxene (± plagioclase) derived from ocean island basalts (OIB)-like magmas, and variations in the Sr and Nd isotope compositions suggest as much as 20% crustal contamination. The bulk of the Nd–Sr–Hf and Pb isotopic data form a tight cluster between a depleted mantle end-member (HIMU, high-U/Pb mantle) and an enriched mantle (EMI) end-member and are thought to reflect a sub-continental lithospheric mantle that was metasomatized by a convecting asthenospheric plume. Variations in these isotopic compositions along the west–east axis of the Monteregian Province (from the Oka carbonatite to the Mount Shefford intrusion) may reflect various degrees of mixing between HIMU and EMI enriched mantle reservoirs. Anomalously low 207Pb/204Pb and 208Pb/204Pb isotopic ratios from some of the intrusions likely indicate incorporation of an Archean component within the lithospheric mantle. We propose a model in which Monteregian magmatism formed from melting of a predominantly Proterozoic metasomatized lithospheric mantle in response to lithospheric extension during the opening of the North Atlantic Ocean at ca. 124 Ma.
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Hindshaw, Ruth S., Nicholas J. Tosca, Alexander M. Piotrowski, and Edward T. Tipper. "Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard)." Earth Surface Dynamics 6, no. 1 (2018): 141–61. http://dx.doi.org/10.5194/esurf-6-141-2018.
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Abstract. The identification of sediment sources to the ocean is a prerequisite to using marine sediment cores to extract information on past climate and ocean circulation. Sr and Nd isotopes are classical tools with which to trace source provenance. Despite considerable interest in the Arctic Ocean, the circum-Arctic source regions are poorly characterised in terms of their Sr and Nd isotopic compositions. In this study we present Sr and Nd isotope data from the Paleogene Central Basin sediments of Svalbard, including the first published data of stream suspended sediments from Svalbard. The stream suspended sediments exhibit considerable isotopic variation (εNd = −20.6 to −13.4; 87Sr ∕ 86Sr = 0.73421 to 0.74704) which can be related to the depositional history of the sedimentary formations from which they are derived. In combination with analysis of the clay mineralogy of catchment rocks and sediments, we suggest that the Central Basin sedimentary rocks were derived from two sources. One source is Proterozoic sediments derived from Greenlandic basement rocks which are rich in illite and have high 87Sr ∕ 86Sr and low εNd values. The second source is Carboniferous to Jurassic sediments derived from Siberian basalts which are rich in smectite and have low 87Sr ∕ 86Sr and high εNd values. Due to a change in depositional conditions throughout the Paleogene (from deep sea to continental) the relative proportions of these two sources vary in the Central Basin formations. The modern stream suspended sediment isotopic composition is then controlled by modern processes, in particular glaciation, which determines the present-day exposure of the formations and therefore the relative contribution of each formation to the stream suspended sediment load. This study demonstrates that the Nd isotopic composition of stream suspended sediments exhibits seasonal variation, which likely mirrors longer-term hydrological changes, with implications for source provenance studies based on fixed end-members through time.
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Nedosekova, I. L., V. A. Koroteev, T. B. Bayanova, P. A. Serov, V. I. Popova, and M. V. Chervyakovskaya. "On the age of pyrochlore carbonatites from the Ilmeno-Vishnevogorsky Alkaline Complex, the Southern Urals (insights from Rb-Sr and Sm-Nd isotopic data)." LITHOSPHERE (Russia) 20, no. 4 (2020): 486–98. http://dx.doi.org/10.24930/1681-9004-2020-20-4-486-498.
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Research subject. In this research, we carried out Sm-Nd- и Rb-Sr-dating of pyrochlore carbonatite from the Vishnevogorsky niobium deposit, Ilmeno-Vishnevogorsky Alkaline Complex, Southern Urals. IVC is located in the Ural fold region and is a carbonatite complex of the linear type. Rare metal (Nb-Zr-TR) deposits and occurrences are related to IVC. The age and the duration of IVC deposits formation remains a matter of debate. To determine the age of IVC carbonatites and related niobium ore, we measured Sm-Nd and Rb-Sr isotopic compositions and concentrations of the elements in the minerals (pyrochlore, calcite, apatite, biotite) and bulk sample of pyrochlore carbonatite. Materials and methods. The Sm and Nd isotopic compositions and concentrations were determined on a Finnigan MAT-262L (RPQ) seven-collector mass spectrometer in the static regime at the Geological Institute of the Kola Scientific Center, Apatity, Russia. The Sr and Rb isotopic compositions and concentrations were determined on thermos-ionization mass spectrometer Triton Plus (“Geoanalitik”, IGG UD RAN, Ekaterinburg, Russia). Results. Age of pyrochlore carbonatites from ore zone 140 (Vishnevogorsky deposit, IVC) defined by Sm-Nd and Rb-Sr isotopic methods. Mineral Sm-Nd-isochron (5 points) indicated age 229 ± 16 Ma, mineral Rb-Sr-isochron (5 points) showed similar age 250.5 ± 1.2 Ma. Conclusions. Results Sm-Nd и Rb-Sr dating indicate that the pyrochlore сarbonatites of ore zone 140 crystallized ≈ 250 Ma ago, at the stage of the postcollisional extension, possibly, in connection with exhumation complex, which was accompanied by decompression, partial melting of rocks, involving fluids, dissolution and precipitation of Ordovician-Silurian alkaline-carbonatitе complex. Thus, the formation of the IVC carbonatites and related Nb-ore, which began in Silurian (S), continued in Permian (P) and Triassic (T1-2) and was associated with the post-collision stage of tectonic activity in the Ural Fold Belt.
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Chen, Shuang-Shuang, Tong Hou, Jia-Qi Liu, and Zhao-Chong Zhang. "Geochemical Variation of Miocene Basalts within Shikoku Basin: Magma Source Compositions and Geodynamic Implications." Minerals 11, no. 1 (2020): 25. http://dx.doi.org/10.3390/min11010025.
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Shikoku Basin is unique as being located within a trench-ridge-trench triple junction. Here, we report mineral compositions, major, trace-element, and Sr-Nd-Pb isotopic compositions of bulk-rocks from Sites C0012 (>18.9 Ma) and 1173 (13–15 Ma) of the Shikoku Basin. Samples from Sites C0012 and 1173 are tholeiitic in composition and display relative depletion in light rare earth elements (REEs) and enrichment in heavy REEs, generally similar to normal mid-ocean ridge basalts (N-MORB). Specifically, Site C0012 samples display more pronounced positive anomalies in Rb, Ba, K, Pb and Sr, and negative anomalies in Th, U, Nb, and Ta, as well as negative Nb relative to La and Th. Site 1173 basalts have relatively uniform Sr-Nd-Pb isotopic compositions, close to the end member of depleted mantle, while Site C0012 samples show slightly enriched Sr-Nd-Pb isotopic signature, indicating a possible involvement of enriched mantle 1 (EM1) and EM2 sources, which could be attributed to the metasomatism of the fluids released from the dehydrated subduction slab, but with the little involvement of subducted slab-derived sedimentary component. Additionally, the Shikoku Basin record the formation of the back-arc basin was a mantle conversion process from an island arc to a typical MORB. The formation of the Shikoku Basin is different from that of the adjacent Japan Sea and Parece Vela Basin, mainly in terms of the metasomatized subduction-related components, the nature of mantle source, and partial melting processes.
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DU, ZHIHENG, CUNDE XIAO, MINGHU DING, and CHUANJIN LI. "Identification of multiple natural and anthropogenic sources of dust in snow from Zhongshan Station to Dome A, East Antarctica." Journal of Glaciology 64, no. 248 (2018): 855–65. http://dx.doi.org/10.1017/jog.2018.72.
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ABSTRACTThe stable oxygen isotope composition, major ions and isotopic compositions of strontium (Sr), neodymium (Nd) and lead (Pb) in insoluble dust from recent surface snow samples along the transect from the Zhongshan and Progress stations (located on the Amery Ice Shelf, East Antarctica) to Dome A (Summit, Antarctica) were analysed. No previous isotopic fingerprinting studies have been conducted for this transect. These data were used to document the dust provenances in Antarctica along the transect up to the highest site, Dome A, for the first time. The insoluble dust in snow samples along the coast displays an overall crust-line isotopic signature that is characterised by highly radiogenic 87Sr/86Sr values and less radiogenic 143Nd/144Nd values. These signatures are comparable with those of samples collected near the ice-free areas of the Zhongshan and Progress stations. Spatial differences are statistically significant along the transect, and the Sr, Nd and Pb isotope components in insoluble dust from two continuous snow samples at Dome A exhibit marked differences, indicating that additional dust reaches the East Antarctic Plateau. The isotopic characteristics of insoluble dust from this transect indicate that the long-distance natural dust and anthropogenic pollutants in these samples primarily originate from Australia.
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XIONG, LE, JUNHAO WEI, WENJIE SHI, et al. "Geochronology, petrology and geochemistry of the Mesozoic Dashizhuzi granites and lamprophyre dykes in eastern Hebei – western Liaoning: implications for lithospheric evolution beneath the North China Craton." Geological Magazine 155, no. 7 (2017): 1542–65. http://dx.doi.org/10.1017/s0016756817000437.
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AbstractGeochronological, elemental and isotopic data of the Dashizhuzi granites and lamprophyre dykes from the eastern Hebei – western Liaoning on the northern North China Craton (NCC) provide an insight into the nature of their magma sources and subcontinental lithospheric mantle. The Dashizhuzi granites have an emplacement age of 226 Ma. They have enriched lithospheric mantle type 1 (EM1-like) Sr–Nd isotopic compositions, and have distinctive features of high Na2O and Sr and low Y with high Sr/Y and (La/Yb)N ratios. These characteristics show that the Dashizhuzi granites originated directly from melting of mafic lower crust composed of pre-existing ancient crustal and enriched mantle-derived juvenile crustal materials at normal continental crustal depth of 33–40 km. The lamprophyre dykes are dated at 167 Ma, and can be divided into two groups. The Group 1 dykes have variable Sr–Nd isotopic compositions and mid-ocean-ridge basalt (MORB-) like Th/U, Ba/Th and Ce/Pb ratios, whereas the Group 2 dykes have enriched Sr–Nd isotopic compositions and notable high Co, Cr, MgO and low Al2O3 characteristics. These distinctive features suggest that the Group 1 dykes were derived from a relatively fertile lithospheric mantle source (garnet-facies amphibole-bearing lherzolite) which has experienced variable degrees of asthenospheric mantle-derived melt–peridotite interaction prior to melting. However, the Group 2 dykes were derived from an ancient garnet-facies phlogopite and/or amphibole-bearing lherzolite lithospheric mantle. Thinning of the Early Mesozoic lithospheric mantle beneath the northern NCC is dominantly through melt–peridotite interaction and thermo-mechanical erosion prior to Middle Jurassic time. The chemical compositions have been modified at the bottom of the lithospheric mantle through melt–peridotite interaction processes.
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Giuliani, Andrea, Matthew G. Jackson, Angus Fitzpayne, and Hayden Dalton. "Remnants of early Earth differentiation in the deepest mantle-derived lavas." Proceedings of the National Academy of Sciences 118, no. 1 (2020): e2015211118. http://dx.doi.org/10.1073/pnas.2015211118.
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The noble gas isotope systematics of ocean island basalts suggest the existence of primordial mantle signatures in the deep mantle. Yet, the isotopic compositions of lithophile elements (Sr, Nd, Hf) in these lavas require derivation from a mantle source that is geochemically depleted by melt extraction rather than primitive. Here, this apparent contradiction is resolved by employing a compilation of the Sr, Nd, and Hf isotope composition of kimberlites—volcanic rocks that originate at great depth beneath continents. This compilation includes kimberlites as old as 2.06 billion years and shows that kimberlites do not derive from a primitive mantle source but sample the same geochemically depleted component (where geochemical depletion refers to ancient melt extraction) common to most oceanic island basalts, previously called PREMA (prevalent mantle) or FOZO (focal zone). Extrapolation of the Nd and Hf isotopic compositions of the kimberlite source to the age of Earth formation yields a143Nd/144Nd-176Hf/177Hf composition within error of chondrite meteorites, which include the likely parent bodies of Earth. This supports a hypothesis where the source of kimberlites and ocean island basalts contains a long-lived component that formed by melt extraction from a domain with chondritic143Nd/144Nd and176Hf/177Hf shortly after Earth accretion. The geographic distribution of kimberlites containing the PREMA component suggests that these remnants of early Earth differentiation are located in large seismically anomalous regions corresponding to thermochemical piles above the core–mantle boundary. PREMA could have been stored in these structures for most of Earth’s history, partially shielded from convective homogenization.
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Lambert, R. StJ, V. E. Chamberlain, and J. G. Holland. "Ferro-andesites in the Grande Ronde Basalt: their composition and significance in studies of the origin of the Columbia River Basalt Group." Canadian Journal of Earth Sciences 32, no. 4 (1995): 424–36. http://dx.doi.org/10.1139/e95-036.
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Flows from the Grande Ronde Basalt of the Columbia River Basalt Group include several with the chemical composition of ferro-andesites. These flows have SiO2 > 55%, MgO < 4%, and also have higher Fe/Mg than the average value for Grande Ronde Basalt. They are also distinctly richer in Cs, Rb, K, Ba, La, Ce, Th, and U than the remainder of the Grande Ronde Basalt flows, and possess small negative Eu anomalies. Their Pb isotopic compositions define a mixing line with a negative slope on a 206Pb/204Pb versus 207Pb/204Pb plot. Their Nd isotopic compositions lie between 143Nd/144Nd = 0.51252 and 0.51264, and their Sr isotopic compositions lie between 87Sr/86Sr = 0.7055 and 0.7060. These values define the enriched end of the Columbia River Basalt Group spectrum on a Sr–Nd epsilon diagram (excluding the Saddle Mountains Basalt). These ferro-andesite flows also form a compositional end member of the Columbia River Basalt Group and are sufficiently distinctive to warrant special consideration. We compare them with lavas from other tholeiitic provinces. Petrogenetically, they can be related to the Grande Ronde Basalt low-Mg basalts by plagioclase fractionation, or by clinopyroxene fractionation in partially melted eclogites. However, the situation may not be that simple, as their unique isotopic compositions are closely related to those of parental mantle materials, perhaps thus requiring separate reservoirs and (or) sources. Extending this argument to other parts of the Columbia River Basalt Group suggests that the origin of these basalts may be in a system of comparatively small magma chambers in the uppermost mantle, frequently replenished from a variety of sources.
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Castorina, F., F. Stoppa, A. Cundari, and M. Barbieri. "An enriched mantle source for Italy's melilitite-carbonatite association as inferred by its Nd-Sr isotope signature." Mineralogical Magazine 64, no. 4 (2000): 625–39. http://dx.doi.org/10.1180/002646100549652.
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AbstractNew Sr-Nd isotope data were obtained from Late Pleistocene carbonatite-kamafugite associations from the Umbria-Latium Ultra-Alkaline District of Italy (ULUD) with the aim of constraining their origin and possible mantle source(s). This is relevant to the origin and evolution of ultrapotassic (K/Na ≫2) and associated rocks generally, notably the occurrences from Ugandan kamafugites,Western Australian lamproites and South African orangeites. The selected ULUD samples yielded 87Sr/86Sr and 143Nd/144Nd ranging from 0.7100 to 0.7112 and from 0.5119 to 0.5121 respectively, similar to cratonic potassic volcanic rocks with higher Rb/Sr and lower Sm/Nd ratios than Bulk Earth. Silicate and carbonate fractions separated from melilitite are in isotopic equilibrium, supporting the view that they are cogenetic. The ULUD carbonatites yielded the highest radiogenic Sr so far reported for carbonatites. In contrast, sedimentary limestones from ULUD basement formations are lower in radiogenic Sr, i.e. 87Sr/86Sr = 0.70745–0.70735. The variation trend of ULUD isotopic compositions is similar to that reported for Ugandan kamafugites and Western Australian lamproites and overlaps the values for South African orangeites in the εSr-εNd diagram. A poor correlation between Sr/Nd and 87Sr/86Sr ratios in ULUD rocks is inconsistent with a mantle source generated by subduction-driven processes, while the negligible Sr and LREE in sedimentary limestones from the ULUD region fail to account for a hypothetical limestone assimilation process. The Nd model ages of 1.5–1.9 Ga have been inferred for a possible metasomatic event, allowing further radiogenic evolution of the source, a process which may have occurred in isolation until eruption time. While the origin of this component remains speculative, the Sr-Nd isotope trend is consistent with a simple mixing process involving an OIB-type mantle and a component with low εNd and high εSr.
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Olive, V., R. Hebert, D. Vermette, and M. Loubet. "Geochemistry of Iapetus volcanic rocks, Quebec Appalachians; Nd, Sr isotopic compositions." American Journal of Science 297, no. 4 (1997): 418–39. http://dx.doi.org/10.2475/ajs.297.4.418.
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Bogina, Maria, Boris Belyatsky, Evgenii Sharkov, Alexey Chistyakov, and Robert Krymsky. "Origin of the Middle Paleoproterozoic Tiksheozero Ultramafic-Alkaline-Carbonatite Complex, NE Fennoscandian Shield: Evidence from Geochemical and Isotope Sr-Nd-Hf-Pb-Os Data." Minerals 11, no. 6 (2021): 570. http://dx.doi.org/10.3390/min11060570.
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This article reports new geochemical, Sr-Nd-Hf-Pb and Re-Os data on the rocks of the Middle Paleoproterozoic (1.99 Ga) Tiksheozero ultramafic-alkaline-carbonatite complex confined to the northeastern margin of the Karelian Craton. We focus on the poorly studied silicate rocks. Based on petrographic and geochemical research, the silicate rocks are subdivided into two groups: an ultramafic-mafic series depleted in REE, and other incompatible elements and an alkaline series enriched in these elements. Isotope studies showed that all rocks have juvenile isotope signatures and were likely derived from a primitive OIB-type mantle source with possible contributions of the subcontinental lithospheric mantle (SCLM). Insignificant crustal contamination is recorded by Pb and Os isotopic compositions. The incompatible element enrichment in the alkaline rocks and depletion in ultramafic-mafic rocks of the mildly alkaline series with allowance for insignificant crustal contamination confirm their derivation from different primary melts. However, a narrow range of Sr, Nd, Hf, and Pb isotope compositions and compact clusters in 207Pb/204Pb-206Pb/204Pb, Nd-87Sr/86Sr and Hf-Nd isotope diagrams indicate their origination from a common mantle source. A model of subsequent two-stage melting is being most consistent with the geochemical data for this complex.
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He, Jun, Xiaochun Xu, Zhongyang Fu, et al. "Decoupling of Sr-Nd Isotopic Composition Induced by Potassic Alteration in the Shapinggou Porphyry Mo Deposit of the Qinling–Dabie Orogenic Belt, China." Minerals 11, no. 8 (2021): 910. http://dx.doi.org/10.3390/min11080910.
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In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even < 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even < −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively.
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Niu, Xiaolu, Yildirim Dilek, Fei Liu, Guangying Feng, and Jingsui Yang. "Early Devonian ultrapotassic magmatism in the North China Craton: geochemical and isotopic evidence for subcontinental lithospheric mantle metasomatism by subducted sediment-derived fluids." Geological Magazine 158, no. 1 (2019): 158–74. http://dx.doi.org/10.1017/s0016756819000797.
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AbstractWe report new U–Pb zircon age data, zircon in situ oxygen isotope, mineral chemistry, whole-rock geochemistry and Sr–Nd isotopic compositions from the Early Devonian ultrapotassic Gucheng pluton in the North China Craton, and discuss its petrogenesis. The Gucheng pluton is exposed in the northern part of the North China Craton and forms a composite intrusion, consisting of K-feldspar-bearing clinopyroxenite, clinopyroxene-bearing syenite and alkali-feldspar syenite. Mineral phases in these lithologies include clinopyroxene (Wo43–48En19–35Fs18–38), sanidine (An0Ab3–11Or89–97), and subordinate titanite, andradite and Na-feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in situ oxygen isotopes (δ18O = 5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the North China Craton. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo-Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean-type continental margin evolution along the northern edge of the North China Craton facing the Palaeo-Asian Ocean.
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PE-PIPER, GEORGIA, and DAVID J. W. PIPER. "Late Cenozoic, post-collisional Aegean igneous rocks: Nd, Pb and Sr isotopic constraints on petrogenetic and tectonic models." Geological Magazine 138, no. 6 (2001): 653–68. http://dx.doi.org/10.1017/s0016756801005957.
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Nd isotopic composition has been determined for 16 igneous rocks, representing the wide geochemical, spatial and temporal range of post-collisional, late Cenozoic magmas in the Aegean area. Nd isotopes are used to further interpret previously published Pb and Sr isotope data. The overall pattern of late Cenozoic volcanism resulted from rapid extension, with thermal effects causing melting of hydrated, enriched, subcontinental lithosphere to produce widespread K-rich magmas. Slab break-off and intrusion of hot asthenosphere caused partial melting of rift-related continental margin basalts at the detachment point to generate adakitic magmas. Further outboard, mafic magma from enriched lithospheric mantle melted thickened lower crust to produce the granitoid plutons of the Cyclades. Nd isotopic variation in these varied rock types correlates with pre-Cenozoic palaeo-geography. Proterozoic subduction-related enrichment in Th and U, together with other large-ion lithophile elements, produced distinctive Pb isotope composition. This was later modified where Mesozoic subduction of terrigenous sediment was important, whereas subduction of oceanic carbonate sediments produced enrichment in radiogenic Sr and low Ce/Sr ratios. Late Cenozoic magmas sourced in eastern Pelagonian zone sub-continental lithospheric mantle have Nd model ages of about 1.0 Ga, and generally high 87Sr/86Sr and high 207Pb/204Pb (∼ 15.68) and 208Pb/204Pb (∼ 39.0) for low 206Pb/204Pb (∼ 18.6), but rocks to the west have more radiogenic Pb and higher Ce/Sr as a result of greater subduction of terrigenous sediment from the northern Pindos ocean. Magmas sourced from sub-continental lithosphere beneath the Apulian continental block were strongly influenced by subduction of oceanic crust and sediments north of the passive margin of north Africa. Subduction of Nile-derived terrigenous sediment in the east resulted in Nd model ages of 0.7 to 0.8 Ga and radiogenic Pb isotopes. Greater subduction of oceanic carbonate in the west resulted in magmas with higher 87Sr/86Sr and lower Ce/Sr. The strongly negative εNd for adakites in the central Aegean rules out a source from subducted oceanic basalt, and the adakite magma was probably derived from melting of hydrated Triassic sub-alkaline basalt of continental origin. Where trachytic rocks are succeeded by nepheline-normative basalts (e.g. Samos), Nd isotope data imply that early partial melting of the enriched subcontinental lithospheric mantle involved hydrous amphibole and phlogopite, but once these minerals were consumed, younger magmas were produced by partial melting dominated by olivine and orthopyroxene.
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Mohr, Peter. "Cryptic Sr and Nd isotopic variation across the Leinster Granite, southeast Ireland." Geological Magazine 128, no. 3 (1991): 251–56. http://dx.doi.org/10.1017/s0016756800022093.
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AbstractRb–Sr isotope whole-rock data from the end-Caledonian Leinster Batholith define an errorchron age of 464±26 Ma, appreciably older than the accepted emplacement age of c. 405 Ma. This anomalously old age is the consequence of a highly variable initial Sr isotopic composition. Initial Nd ratios and TDM model ages also show a wide range of values. However, these isotopic variations are neither randomly distributed nor related to petrographic changes but instead reflect, in a simple way, geographic position about the axis of the batholith. The isotopic pattern revealed in the Leinster Batholith means that isochron ages obtained from S-type granites may be largely dependent on the sampling scheme adopted. The variable isotopic composition of the granite most likely resulted from either a heterogeneous metasedimentary source or hybridization of coeval, dominantly crustal melts.
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Baskina, V. A., Yu V. Gol’tsman, and E. D. Bairova. "Sr and Nd isotopic compositions and sources of basalts of southern Primorye." Doklady Earth Sciences 413, no. 2 (2007): 406–9. http://dx.doi.org/10.1134/s1028334x07030191.
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Zhou, Taixi, Jiangfeng Chen, Xun Zhang, Yin Liu, and Fuquan Jin. "Nd and Sr isotopic compositions of basalts from the Alatao Pass, Xinjiang." Chinese Science Bulletin 42, no. 10 (1997): 878–79. http://dx.doi.org/10.1007/bf02882506.
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Leat, P. T., R. N. Thompson, M. A. Morrison, G. L. Hendry, and A. P. Dickin. "Silicic Magmas Derived by Fractional Crystallization from Miocene Minette, Elkhead Mountains, Colorado." Mineralogical Magazine 52, no. 368 (1988): 577–85. http://dx.doi.org/10.1180/minmag.1988.052.368.03.
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AbstractThe rock association of minette with silicic lavas and intrusions (granites, syenites, dacites) is a common geologic feature in both collisional and extensional tectonic settings. Considerable doubt exists as to whether a genetic link exists between these mafic and silicic rocks. We describe a Miocene sill from NW Colorado which is a clear example of a mixed magma consisting of originally-liquid inclusions of minette in a silicic trachydacite host. Chemical and Sr, Nd and Pb isotopic data are consistent with derivation of the silicic host magma of the sill dominantly by fractional crystallization of the minette magma. Correlations between the elemental compositions of the rock types and their Sr and Nd isotopic ratios imply minor assimilation of continental crust with relatively low values of both 87Sr/86Sr and 143Nd/144Nd, concomitantly with fractional crystallization. The parental minette magma was probably derived by partial melting of subcontinental lithospheric mantle. While the sill was emplaced in a rift-like tectonic setting, the chemical and isotopic composition of the lithosphere-derived minette magmas (and hence the silicic fractionates) was largely independent of this setting, but dependent upon the composition and age of the lithospheric mantle and crust.
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BONEV, NIKOLAY, YILDIRIM DILEK, JOHN M. HANCHAR, KAMEN BOGDANOV, and LASLO KLAIN. "Nd–Sr–Pb isotopic composition and mantle sources of Triassic rift units in the Serbo-Macedonian and the western Rhodope massifs (Bulgaria–Greece)." Geological Magazine 149, no. 1 (2011): 146–52. http://dx.doi.org/10.1017/s0016756811000938.
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AbstractWe report on the field occurrence and isotopic compositions of metamafic rocks exposed in the Serbo-Macedonian (Volvi and Therma bodies) and western Rhodope (Rila Mountains) massifs of Bulgaria and Greece. These metamafic units consist of high- and low-Ti gabbroic and basaltic rocks, whose Nd–Sr–Pb isotopes are compatible with mantle-derived MORB and OIB components with a small amount of crustal material involved in their melt source. These isotopic features combined with the field observations are consistent with an intra-continental rift origin of the metamafic rocks protolith, and are comparable to those of the Triassic rift-related mafic rocks in the northern Aegean region.
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Smith, Alan D., Alan D. Brandon, and Richard StJ Lambert. "Nd–Sr isotope systematics of Nicola Group volcanic rocks, Quesnel terrane." Canadian Journal of Earth Sciences 32, no. 4 (1995): 437–46. http://dx.doi.org/10.1139/e95-037.
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Volcanic rocks of the Nicola Group belong to an arc built on the western margin of the Quesnel terrane in the Late Triassic to Early Jurassic. Low-K – high-K compositional types define a Rb–Sr isochron of 222 ± 15 Ma with initial 87Sr/86Sr = 0.70367 ± 2. The corresponding Nd isotopic compositions of these samples (εNd(222 Ma) = +5.1 to +7.8) fall within the range for early Mesozoic island arcs. A comparable range of εNd(222 Ma) (+5.0 to +7.9) in picrite–shoshonite samples precludes generation of increasingly potassic magmas by progressive metasomatism of the mantle wedge alone. Source-region heterogeneity, possibly imparted by changes in the composition of subducted slab components or interaction with amphibole or phlogopite in the source remnant of an earlier (Permian) arc on the Quesnel terrane, is required to account for geochemical differences between these rock suites. Crustal contamination is severely limited from the high εNd values, such that continental basement now underlying the Quesnel terrane is likely an artifact of later terrane obduction.
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Nagatsuka, Naoko, Nozomu Takeuchi, Ki-Cheol Shin, and Takanori Nakano. "Spatial variations of Sr–Nd isotopic ratios, mineralogical and elemental compositions of cryoconite in an Alaskan glacier." Annals of Glaciology 59, no. 77 (2018): 147–58. http://dx.doi.org/10.1017/aog.2019.2.
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ABSTRACTTo understand the geological origins of minerals in cryoconite and the nutrients sources for microbes on glaciers, we analyzed the Sr–Nd isotopic ratios of the four mineral fractions in cryoconites including saline, carbonate, phosphate, silicate and the organic fraction obtained from Gulkana Glacier in Alaska. The isotopes in the silicate mineral fraction exhibited spatial variation within the glacier (87Sr/86Sr: 0.704533–0.709563, εNd (0): −16.0 to 0.5), which can be explained by the different mixing ratios of the two distinct sources: one of the sources is lateral and terminal moraines or soil, and the other is the medial moraine of the glacier. The minerals in the cryoconite at the lower sites in the glacier are likely derived from the former source, whereas those at the upper sites are from latter sources. The mineralogical and elemental compositions also support mixing of the silicate minerals from the two local sources. The Sr isotopic ratios of the organic fraction also showed spatial variation on the glacier in the middle sites – a trend similar to those of the phosphate fraction. The results suggest that the organic matter is mostly the byproducts of microbes using the phosphate minerals as a nutrient source.
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Jahn, Bor-ming, Fuyuan Wu, and Bin Chen. "Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 1-2 (2000): 181–93. http://dx.doi.org/10.1017/s0263593300007367.
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The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calcalkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion.Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive εNd(T) values and young Sm—Nd model ages (TDM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their ‘juvenile’ character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative εNd(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes.The evolution of the CAOB is probably related to accretion of young arc complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.
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Speziale, Sergio, Francesca Castorina, Paolo Censi, Celso de Barros Gomes, Leila Soares Marques, and Piero Comin-Chiaramonti. "Carbonatites from the southern Brazilian Platform: A review. II: Isotopic evidences." Open Geosciences 12, no. 1 (2020): 678–702. http://dx.doi.org/10.1515/geo-2020-0032.
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AbstractEarly and Late Cretaceous alkaline and alkaline–carbonatitic complexes from southern Brazil are located along the main tectonic lineaments of the South America Platform. Calcium-, magnesium-, and ferrocarbonatites are well represented and frequently associated even in the same complex. Primary carbonates present significant variations in C–O isotopic compositions, which are mainly due to isotope exchange with H2O–CO2-rich hydrothermal fluids, whereas fractional crystallization or liquid immiscibility probably affects the δ18O and δ13C values by no more than 2δ‰. Our isotope exchange model implies that the most significant isotopic variations took place in a hydrothermal environment, e.g., in the range 400–80°C, involving fluids with the CO2/H2O ratio ranging from 0.8 to 1. Sr–Nd–Pb isotope systematics highlight heterogeneous mixtures between HIMU and EMI mantle components, similar to the associated alkaline rocks and the flood tholeiites from southern Brazil. In spite of the strong variation shown by C–O isotopes, Sr–Nd–Pb–Os isotopic systematics could be related to an isotopically enriched source where the chemical heterogeneities reflect a depleted mantle “metasomatized” by small-volume melts and fluids rich in incompatible elements. These fluids are expected to have promoted crystallization of K-rich phases in the mantle, which produced a veined network variously enriched in LILE and LREE. The newly formed veins (enriched component) and peridotite matrix (depleted component) underwent a different isotopic evolution with time as reflected by the carbonatites. These conclusions may be extended to the whole Paraná–Etendeka system, where isotopically distinct parent magmas were generated following two main enrichment events of the subcontinental lithospheric mantle at 2.0–1.4 and 1.0–0.5 Ga, respectively, as also supported by Re–Os systematics. The mantle sources preserved the isotopic heterogeneities over a long time, suggesting a nonconvective lithospheric mantle beneath different cratons or intercratonic regions. Overall, the data indicate that the alkaline–carbonatitic magmatism originated from a locally heterogeneous subcontinental mantle.
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Geagea, M. Lahd, P. Stille, M. Millet, and Th Perrone. "REE characteristics and Pb, Sr and Nd isotopic compositions of steel plant emissions." Science of The Total Environment 373, no. 1 (2007): 404–19. http://dx.doi.org/10.1016/j.scitotenv.2006.11.011.
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Macdougall, J. D., and Stephen E. Haggerty. "Ultradeep xenoliths from African kimberlites: Sr and Nd isotopic compositions suggest complex history." Earth and Planetary Science Letters 170, no. 1-2 (1999): 73–82. http://dx.doi.org/10.1016/s0012-821x(99)00091-6.
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Bell, Keith, and John Blenkinsop. "Nd and Sr isotopic compositions of East African carbonatites: Implications for mantle heterogeneity." Geology 15, no. 2 (1987): 99. http://dx.doi.org/10.1130/0091-7613(1987)15<99:nasico>2.0.co;2.
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Garçon, Marion, Catherine Chauvel, Christian France-Lanord, Mara Limonta, and Eduardo Garzanti. "Which minerals control the Nd–Hf–Sr–Pb isotopic compositions of river sediments?" Chemical Geology 364 (January 2014): 42–55. http://dx.doi.org/10.1016/j.chemgeo.2013.11.018.
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Yang, ShouYe, ShaoYong Jiang, HongFei Ling, XiaoPing Xia, Min Sun, and DeJie Wang. "Sr-Nd isotopic compositions of the Changjiang sediments: Implications for tracing sediment sources." Science in China Series D: Earth Sciences 50, no. 10 (2007): 1556–65. http://dx.doi.org/10.1007/s11430-007-0052-6.
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Roden, Michael F., V. Rama Murthy, and Jose C. Gaspar. "Sr and Nd Isotopic Composition of the Jacupiranga Carbonatite." Journal of Geology 93, no. 2 (1985): 212–20. http://dx.doi.org/10.1086/628943.
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CINTRON FRANQUI, NADJA OMARA, SUNG HI CHOI, and DER-CHUEN LEE. "Peridotites and basaltic rocks within an ophiolitic mélange from the SW igneous province of Puerto Rico: relation to the evolution of the Caribbean Plate." Geological Magazine 154, no. 1 (2016): 96–118. http://dx.doi.org/10.1017/s001675681500093x.
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AbstractThe geology of Puerto Rico is divided into three regions: the north, central and SW igneous provinces. Characterized by its Jurassic ophiolitic mélange basement, lithology of the SW Igneous Province (SIP) is not related to either of the other two provinces. The ophiolitic mélange is exposed in three peridotite belts: Monte del Estado, Rio Guanajibo and Sierra Bermeja. We present geochemical data to identify the tectonic setting of the SIP peridotite formation and its relation to the evolution of the Caribbean Plate. Comparisons of spinel Cr no. (13–21), Mg no. (63.3–69.6) and TiO2suggest an abyssal peridotite origin; however, only Sierra Bermeja presents high TiO2characteristics of a mid-ocean-ridge-basalt- (MORB-) like melt reaction. Temperatures determined with two-pyroxene geothermometers indicated a cold thermal regime ofc. 800–1050°C, with characteristics of large-offset transform fault abyssal peridotites. The geochemistry and Sr–Nd–Hf–Pb isotopic compositions of basalts within the mélange were also analysed. Las Palmas amphibolites exhibited normal-MORB-like rare earth element (REE) and trace-element patterns, whereas metabasalts and Lower Cajul basalts exhibited island-arc tholeiitic-like patterns. Highly radiogenic Sr isotopes (0.70339–0.70562) of the basalts suggest seawater alteration; however, Pb–Pb and Nd–Hf isotope correlations represent the primary compositions of a Pacific/Atlantic MORB source for the amphibolites, metabasalts and Lower Cajul basalts. We propose that the SIP ophiolitic mélange was formed along a large-offset transform fault, which initiated subduction and preserved both proto-Pacific and proto-Caribbean lithospheric mantle. Younger Upper Cajul basalts exhibited enriched-MORB-like geochemical and isotopic signatures, which can be attributed to a tectonized Caribbean ocean plateau.
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Ripp, G. S., I. A. Izbrodin, M. O. Rampilov, A. A. Tomilenko, E. A. Lastochkin, and V. F. Posokhov. "Relationship of F-Be mineralization to granites and syenites at the Ermakovka deposit (Western Transbaikalia)." Geologica Acta 18 (January 29, 2020): 1–13. http://dx.doi.org/10.1344/geologicaacta2020.18.2.
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The paper presents the mineralogical and geochemical characteristics of two groups of hydrothermal rocks and their relation with subalkaline granites of the Ermakovskoe deposit. The first group includes fluorite-phenakite-bertrandite ore bodies, occurring outside the granite massif. The second group is presented by silicification bodies with sulfates, phosphates, kaolinite, muscovite and hematite. It bears REE (rare earth elements) mineralization (monazite, florencite, xenotime) and occurs within the massif. Our research included isotopic analyses of Sr, Nd and O, studies of trace, including rare-earth element compositions and age determination (U-Pb) of apatite from F-Be ores. Geochemical and isotopic studies are not according with relation between F-Be ores and granites. This is proven by the absence of Be-mineralization in granites and schlieren pegmatites, and a sharp difference in composition of their fluid phases. A reductive fluid specification forming F-Be ores (containing CH4, H2, N2, CO2 and H2S), contrasts sharply with fluid specification of granites. The granites are characterized by high oxygen fugacity, due to ferrous iron, sulfates and phosphates. Besides isotopic composition of oxygen in quartz (7.4 and 5.1‰ δ18О V-SMOW respectively), initial Sr ratios (0.7056-0.7065 and 0.707-0.709 respectively) and REE compositions are different.
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Bell, K., A. N. Zaitsev, J. Spratt, S. Fröjdö, and A. S. Rukhlov. "Elemental, lead and sulfur isotopic compositions of galena from Kola carbonatites, Russia – implications for melt and mantle evolution." Mineralogical Magazine 79, no. 2 (2015): 219–41. http://dx.doi.org/10.1180/minmag.2015.079.2.01.
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AbstractGalena from four REE-rich (Khibina, Sallanlatvi, Seblyavr, Vuoriyarvi) and REE-poor (Kovdor) carbonatites, as well as hydrothermal veins (Khibina) all from the Devonian Kola Alkaline Province of northwestern Russia was analysed for trace elements and Pb and S isotope compositions. Microprobe analyses show that the only detectable elements in galena are Bi and Ag and these vary from not detectable to 2.23 and not detectable to 0.43 wt.% respectively. Three distinct galena groups can be recognized using Bi and Ag contents, which differ from groupings based on Pb isotope data. The Pb isotope ratios show significant spread with 206Pb/204Pb ratios (16.79 to 18.99), 207Pb/204Pb (15.22 to 15.58) and 208Pb/204Pb ratios (36.75 to 38.62). A near-linear array in a 207Pb/204Pb vs.206Pb/204Pb ratio diagram is consistent with mixing between distinct mantle sources, one of which formed during a major differentiation event in the late Archaean or earlier. The S isotopic composition (δ34S) of galena from carbonatites is significantly lighter (–6.7 to –10.3% Canyon Diablo Troilite (CDT) from REE-rich Khibina, Seblyavr and Vuoriyarvi carbonatites, and – 3.2% CDT from REE-poor Kovdor carbonatites) than the mantle value of 0%. Although there is no correlation between S and any of the Pb isotope ratios, Bi and Ag abundances correlate negatively with δ34S values. The variations in the isotopic composition of Pb are attributed to partial melting of an isotopically heterogeneous mantle source, while those of δ34S (together with Bi and Ag abundances) are considered to be process driven. Although variation in Pb isotope values between complexes might reflect different degrees of interaction between carbonatitic melts and continental crust or metasomatized lithosphere, the published noble gas and C, O, Sr, Nd and Hf isotopic data suggest that the variable Pb isotope ratios are best attributed to isotopic differences preserved within a sub-lithospheric mantle source. Different Pb isotopic compositions of galena from the same complex are consistent with a model of magma replenishment by carbonatitic melts/fluids each marked by quite different Pb isotopic compositions.
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Lei, Ming, Zhengfu Guo, Wenbin Zhao, Maoliang Zhang, and Lin Ma. "Coexisting Late Cenozoic Potassic and Sodic Basalts in NE China: Role of Recycled Oceanic Components in Intraplate Magmatism and Mantle Heterogeneity." Lithosphere 2020, no. 1 (2020): 1–28. http://dx.doi.org/10.2113/2020/8875012.
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Abstract This study presents an integrated geochemical study of the Wudalianchi-Erkeshan potassic basalts and Halaha sodic basalts of NE China, and uses these data to further our understanding of the petrogenetic relationships between the coeval potassic and sodic basalts in this region. The potassic basalts with high concentrations of K2O have arc-like trace-element compositions and enriched Sr-Nd-Hf isotopic compositions with unradiogenic 206Pb/204Pb values (16.77–16.90). In contrast, the sodic basalts with high concentrations of Na2O have OIB-like trace-element compositions and depleted Sr-Nd-Hf isotopic compositions with radiogenic 206Pb/204Pb values (18.27–18.40). These data suggest that the potassic and sodic basalts were derived from mixed depleted mid-ocean-ridge basalt mantle (DMM) and enriched mantle source end-members, where the enriched end-members are ancient sediment for the potassic basalts and Pacific oceanic crust for the sodic basalts. The combined geophysical and geochemical data indicate that these two enriched end-members are located in the mantle transition zone. We propose that partial melting of upwelling asthenospheric mantle comprising ambient DMM and recycled materials shifting from the ancient sediment to the Pacific oceanic crust could have produced the coeval potassic and sodic basalts in NE China. The proposed mantle sources for the potassic and sodic basalts indicate that the upper mantle beneath NE China was highly heterogeneous during late Cenozoic.
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SHELLNUTT, J. GREGORY, TUNG-YI LEE, CHIH-CHENG YANG, et al. "Late Permian mafic rocks identified within the Doba basin of southern Chad and their relationship to the boundary of the Saharan Metacraton." Geological Magazine 152, no. 6 (2015): 1073–84. http://dx.doi.org/10.1017/s0016756815000217.
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AbstractThe Doba gabbro was collected from an exploration well through the Cretaceous Doba basin of southern Chad. The gabbro is composed mostly of plagioclase, clinopyroxene and Fe–Ti oxide minerals and displays cumulus mineral textures. Whole-rock40Ar–39Ar step-heating geochronology yielded a Late Permian plateau age of 257 ± 1 Ma. The major and trace elemental geochemistry shows that the gabbro is tholeiitic in composition and has trace element ratios (i.e. La/YbN> 7; Sm/YbPM> 3.4; Nb/Y > 1; Zr/Y > 5) indicative of a basaltic melt derived from a garnet-bearing mantle source. The moderately enriched Sr–Nd isotopes (i.e. ISr= 0.70495 to 0.70839; ɛNd(T)= −1.0 to −1.3) fall within the mantle array (i.e. OIB-like) and are similar to other Late Permian plutonic rocks of North-Central Africa (i.e. ISr= 0.7040 to 0.7070). The enriched isotopic composition of the Doba gabbro contrasts with the more depleted compositions of the spatially associated Neoproterozoic post-Pan-African within-plate granites. The contrasting Nd isotope composition between the older within-plate granites and the younger Doba gabbro indicates that different mantle sources produced the rocks and thus may mark the southern boundary of the Saharan Metacraton.
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BRUNI, SANDRO, MASSIMO D'ORAZIO, MIGUEL J. HALLER, et al. "Time-evolution of magma sources in a continental back-arc setting: the Cenozoic basalts from Sierra de San Bernardo (Patagonia, Chubut, Argentina)." Geological Magazine 145, no. 5 (2008): 714–32. http://dx.doi.org/10.1017/s0016756808004949.
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AbstractEast of the Patagonian Andes, mafic volcanic rocks (mainly lava flows and scoriae) are exposed in the Sierra de San Bernardo fold belt and neighbouring areas (central Patagonia; 44.5–46° S, 69–71° W). They were erupted over a wide interval of time (late Eocene–Pleistocene; 14 new K–Ar ages), and show systematic chemical and Sr–Nd–Pb isotopic variations in time. The alkaline lavas (Mg number 57–66) erupted during the late Eocene and early Miocene, have an intraplate geochemical affinity, and have the highest 143Nd/144Nd and 206Pb/204Pb and the lowest 87Sr/86Sr ratios of the dataset. Their compositions indicate that their depth of equilibration in the mantle was greater than that of subsequent lavas. In contrast, the Plio-Pleistocene alkaline lavas (Mg number 58–71) are the most enriched in incompatible elements, still showing an intra-plate signature, and have the lowest 143Nd/144Nd and 206Pb/204Pb and the highest 87Sr/86Sr ratios. A distinctive group of early Miocene subalkaline lavas is characterized by slightly more evolved compositions (Mg number 56–59), coupled with very low incompatible element contents, flat LREE and fractionated HREE patterns (‘kinked’ pattern), and intermediate Sr–Nd–Pb isotope compositions. The Pleistocene basanites (Mg number 71–72) from the Cerro Ante monogenetic cone, on the easternmost slopes of the Patagonian Andes, have a marked orogenic geochemical signature and Sr–Nd–Pb isotope ratios that overlap with those of volcanic rocks from the adjacent active Andean arc. They originated in a mantle source extensively modified by the addition of materials from the subducting Pacific oceanic plates. We suggest that the wide chemical and isotopic variability of the Sierra de San Bernardo lavas reflects the upwelling of asthenospheric mantle beneath the study area, which induced lithospheric erosion and progressive involvement of enriched mantle domains in the genesis of magmas. In this context, late Eocene and early Miocene alkaline magmatism was dominantly sourced from the asthenospheric mantle, whereas Plio-Pleistocene alkaline magmas contain the largest proportion of an enriched lithospheric component. The peculiar compositional features of the early Miocene subalkaline lavas are interpreted in terms of high-degree mantle melting followed by melt–lithospheric mantle reaction processes. Based on current knowledge about the relative movement and decoupling between lithosphere and asthenosphere, we propose that the asthenosphere below the study area rose up to compensate for the westward drift of the mantle wedge coupled with the South American lithosphere.
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Sevigny, J. H., and R. J. Thériault. "Geochemistry and SrNd isotopic composition of Eocene lamphrophyre dykes, southeastern British Columbia." Canadian Journal of Earth Sciences 40, no. 6 (2003): 853–64. http://dx.doi.org/10.1139/e03-014.
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Mineral compositions, geochemical analyses, and SrNd isotopic compositions are reported for alkaline and calc-alkaline lamprophyres collected along the southern margin of the Valhalla Complex, southeastern British Columbia. The lamprophyres were emplaced during Eocene extension and lithospheric thinning associated with tectonic denudation of the Valhalla Complex. SiO2 contents range from 44.451.6 wt.%, K2O from 1.33.7 wt.%, and volatile contents (H2O + CO2 + SO3) from 0.84.6 wt.%. MgO and Cr contents are 9.57.6 wt.% and 540130 ppm, respectively, for samples with Mg#s between 0.69 and 0.65. Chrondrite-normalized rare-earth element patterns are strongly fractionated with Cen = 120375 and Ybn = 8.412.7. Alkaline lamprophyres contain biotite ± kaersutite ± calcic plagioclase and exhibit a limited range in initial 87Sr/86Sr (0.70510.7057), initial εNd (3.7 to 4.3), and TDM (766796 Ma). Calc-alkaline lamprophyres contain F-rich phlogopite and sodic plagioclase, and exhibit a wider range in initial 87Sr/86Sr (0.70640.7090), initial εNd (6.3 to 11.9), and TDM (9171,614 Ma). Alkaline lamprophyres are interpreted as uncontaminated melts derived from a long-term, volatile, and incompatible element-enriched mantle reservoir. Mantle enrichment coincided with continental rifting of western North America (ca. 760 Ma). The enriched mantle reservoir remained isolated for ~700 Ma. Lamprophyres were generated by partial melting of the mantle reservoir in response to adiabatic decompression and lithospheric thinning during Eocene extension.
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Xu, Wen-Liang, Jia-Hui Chen, Ai-Hua Weng, et al. "Stagnant slab front within the mantle transition zone controls the formation of Cenozoic intracontinental high-Mg andesites in northeast Asia." Geology 49, no. 1 (2020): 19–24. http://dx.doi.org/10.1130/g47917.1.
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Abstract The geochemistry of Cenozoic intracontinental high-Mg andesites (HMAs) in northeast Asia, together with regional geophysical data, offers an opportunity to explore the genetic relationship between the formation of intracontinental HMAs and subduction of the Pacific plate. Compared with primary HMAs in arcs, Cenozoic intracontinental HMAs in northeast Asia have lower Mg# [100 × Mg/(Mg + Fe2+)] values (53–56) and CaO contents (5.8–6.6 wt%), higher alkali (Na2O + K2O) contents (5.15–6.45 wt%), and enriched Sr-Nd-Hf isotopic compositions (87Sr/86Sr = 0.7056–0.7059; εNd = −4.9 to −3.4; εHf = −4.7 to −2.6) as well as lower Pb isotope ratios (206Pb/204Pb = 16.76–19.19; 207Pb/204Pb = 15.42–15.45; 208Pb/204Pb = 36.71–37.11). These Cenozoic intracontinental HMAs are similar to Cenozoic potassic basalts in northeast China with respect to their Sr-Nd-Pb-Hf isotopic compositions but have higher SiO2 and Al2O3 contents and lower K2O, MgO, and light rare earth element contents. These features indicate that these Cenozoic intracontinental HMAs originated from the mantle, where recycled ancient sediments and water contributed to partial melting of peridotite. Combined with the presence of a large low-resistivity anomaly derived from the mantle transition zone (MTZ) near these intracontinental HMAs, and their occurrence above the stagnant slab front within the MTZ (at 600 km depth) in northeast Asia, we conclude that the stagnant slab front, with high contents of recycled ancient sediments and water, has controlled the formation of Cenozoic intracontinental HMAs in northeast Asia.
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Carlson, Richard W., Lars E. Borg, Amy M. Gaffney, and Maud Boyet. "Rb-Sr, Sm-Nd and Lu-Hf isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to the time of Moon formation." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2024 (2014): 20130246. http://dx.doi.org/10.1098/rsta.2013.0246.
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New Rb-Sr, 146,147 Sm- 142,143 Nd and Lu-Hf isotopic analyses of Mg-suite lunar crustal rocks 67667, 76335, 77215 and 78238, including an internal isochron for norite 77215, were undertaken to better define the time and duration of lunar crust formation and the history of the source materials of the Mg-suite. Isochron ages determined in this study for 77215 are: Rb-Sr=4450±270 Ma, 147 Sm- 143 Nd=4283±23 Ma and Lu-Hf=4421±68 Ma. The data define an initial 146 Sm/ 144 Sm ratio of 0.00193±0.00092 corresponding to ages between 4348 and 4413 Ma depending on the half-life and initial abundance used for 146 Sm. The initial Nd and Hf isotopic compositions of all samples indicate a source region with slight enrichment in the incompatible elements in accord with previous suggestions that the Mg-suite crustal rocks contain a component of KREEP. The Sm/Nd— 142 Nd/ 144 Nd correlation shown by both ferroan anorthosite and Mg-suite rocks is coincident with the trend defined by mare and KREEP basalts, the slope of which corresponds to ages between 4.35 and 4.45 Ga. These data, along with similar ages for various early Earth differentiation events, are in accord with the model of lunar formation via giant impact into Earth at ca 4.4 Ga.
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Esperança, Sonia, and Thomas C. Moyer. "Rhyolites as probes of the crust: examples from Tertiary volcanism in Arizona, southwestern U.S.A." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 347–59. http://dx.doi.org/10.1017/s0263593300008014.
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ABSTRACTGeochemical and isotopic data obtained from three bimodal basalt-rhyolite fields in west-central Arizona point to significant variation in the sources of the siliceous products despite petrological similarities between them. The studied fields, which straddle the boundary between the Basin and Range and Colorado Plateau physiographic provinces, include Castaneda Hills (CH) in the Basin and Range, Kaiser Spring (KS) in the Transition Zone, and Mount Floyd (MF) in the Colorado Plateau. Two types of rhyolite (high-silica [HSR] and low-silica [LSR]) occur as lavas in the KS and MF fields, whereas all analysed CH samples are HSR. These lavas generally post-date low-angle extension of the Basin and Range crust and become generally younger towards the Colorado Plateau. Our isotopic data illustrate that the CH rhyolites require a source with comparatively radiogenic Sr, that most rhyolites require a source with comparatively unradiogenic 206Pb/204Pb, and that the MF-HSR require a source with comparatively radiogenic Nd and 206Pb/204Pb. The isotopic data clearly indicate that the western Arizona rhyolites contain a large crustal component. Importantly, the Pb isotopic compositions of the rhyolites illustrate the transition between two crustal provinces identified by other workers on the basis of Nd and Pb isotopic studies of Proterozoic granites. The Sr, Nd, and Pb isotopic compositions of our rhyolites can be modelled by mixing a basaltic component with three hypothetical crustal end-members which themselves may be formed by mixing two crustal components. One crustal component, which is characterised by unradiogenic Pb and Sr, may be similar to the mafic gneiss xenoliths of Tule Tank on the Colorado Plateau. The second crustal component, which has more radiogenic Sr and Pb, may be similar to the Proterozoic Fenner Gneiss of southeastern California. This conceptual model indicates an apparent increase in the contribution of the depleted Tule Tank source from the Basin and Range onto the Colorado Plateau and accommodates the notion that there is an underlying consistency to the petrogeneses of the western Arizona rhyolites as suggested by their chemistry and mineralogy. Although the CH and KS lavas require only one crustal end-member, the MF-HSR and LSR require two isotopically distinct sources. This difference may be attributed to the homogenisation of diverse crustal lithologies by ductile stretching during crustal extension.
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KAWANO, Yoshinobu, Satoshi OKAMURA, Kazuya KUBO, and Hiroo KAGAMI. "Trace elements, Sr and Nd isotopic compositions of the Okushiri granodioritic body, southwest Hokkaido." JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY 88, no. 9 (1993): 447–56. http://dx.doi.org/10.2465/ganko.88.447.
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Jweda, Jason, Louise Bolge, Cornelia Class, and Steven L. Goldstein. "High Precision Sr-Nd-Hf-Pb Isotopic Compositions of USGS Reference Material BCR-2." Geostandards and Geoanalytical Research 40, no. 1 (2015): 101–15. http://dx.doi.org/10.1111/j.1751-908x.2015.00342.x.
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Lapin, A. V., A. V. Tolstov, and A. V. Antonov. "Sr and Nd isotopic compositions of kimberlites and associated rocks of the Siberian craton." Doklady Earth Sciences 414, no. 1 (2007): 557–60. http://dx.doi.org/10.1134/s1028334x07040150.
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CHEN, B., and M. ZHAI. "Geochemistry of late Mesozoic lamprophyre dykes from the Taihang Mountains, north China, and implications for the sub-continental lithospheric mantle." Geological Magazine 140, no. 1 (2003): 87–93. http://dx.doi.org/10.1017/s0016756802007124.
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Many late Mesozoic lamprophyre dykes occur in the Taihang Mountains (north China). These lamprophyres are rich in large ion lithophile elements (e.g. Rb, Sr, Ba and K) and light REE, and have highly differentiated REE patterns. They show large but regular variations in chemical and Nd–Sr isotopic compositions. All these suggest that the lamprophyres were produced from differentiation of a parental magma, coupled with contamination by lower crust. The parental magma was derived from melting of a long-term enriched sub-continental lithospheric mantle source as is indicated by the highly enriched isotopic signatures of the lamprophyres. Mantle enrichment in the area was probably produced by interaction of volatile-rich melts released from the asthenosphere with the above lithosphere in middle Proterozoic times.
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Fang, Xue, Zhigang Zeng, Siyi Hu, et al. "Origin of Pumice in Sediments from the Middle Okinawa Trough: Constraints from Whole-Rock Geochemical Compositions and Sr-Nd-Pb Isotopes." Journal of Marine Science and Engineering 7, no. 12 (2019): 462. http://dx.doi.org/10.3390/jmse7120462.
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Frequent volcanic activity has occurred in the Okinawa Trough (OT) during the late Quaternary, which attracted much attention to the origin of volcanic rocks. Pumice collected from the seafloor has been extensively investigated, whereas few studies paid attention to the pumice in the sediment. The geochemical compositions of pumice preserved in sediments generally provide insight into past volcanic activity and regional magmatism. Here, we present major and trace element compositions and Sr-Nd-Pb isotope data, together with the established age framework for pumice samples recovered from sediment core S9 in the middle OT (MOT) to investigate their possible formation. Compositionally, the S9 pumice samples are dacite and are characterized by relatively higher Sr (87Sr/86Sr = 0.70480–0.70502) and Pb (206Pb/204Pb = 18.321-18.436, 207Pb/204Pb = 15.622–15.624, and 208Pb/204Pb = 38.52–38.63) and lower Nd (143Nd/144Nd = 0.51272–0.51274) isotope compositions than basalts from the MOT. The geochemical compositions of pumice clasts from different layers of core S9 display no temporal variation trends and vary within narrow ranges. On the basis of the geochemical characteristics of S9 pumice samples, we infer that the parent magma of these samples might generate from hybrid magma through an extensive fractional crystallization process. The Indian Ocean MORB-type mantle was first metasomatized by the subducted Philippine Sea sediments to form the primitive magma; then, followed by assimilation of a small amount of lower crustal component occurred in the lower crust. The long-term magmatism and relatively consistent isotopic compositions indicate that a magma chamber might have existed in the lower crust of the MOT between 11.22 and 12.96 cal. ka BP.
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Morishita, Tomoaki, Naoto Hirano, Hirochika Sumino, et al. "Alkali basalt from the Seifu Seamount in the Sea of Japan: post-spreading magmatism in a back-arc setting." Solid Earth 11, no. 1 (2020): 23–36. http://dx.doi.org/10.5194/se-11-23-2020.
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Abstract. We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing basalt dredged from the Seifu Seamount (SSM basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2σ) was obtained for the SSM basalt, indicating that it erupted shortly after the termination of back-arc spreading in the Sea of Japan. The SSM basalt is a high-K to shoshonitic alkali basalt that is characterized by light rare earth element enrichment. The trace element features of the basalt are similar to those of ocean island basalt, although the Yb content is much higher, indicating formation by the low-degree partial melting of spinel peridotite. The Nd, Sr, and Pb isotopic compositions of the SSM basalt differ from those of back-arc basin basalts in the Sea of Japan. The Sr–Nd isotopic composition of the SSM basalt suggests its source was depleted mid-ocean ridge mantle containing an enriched mantle (EM1) component. The SSM basalt was formed in a post-back-arc extension setting by the low-degree partial melting of an upwelling asthenosphere that had previously been associated with the main phase of back-arc magmatism.
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ZHU, YONGFENG, BO CHEN, and TIAN QIU. "Geology and geochemistry of the Baijiantan–Baikouquan ophiolitic mélanges: implications for geological evolution of west Junggar, Xinjiang, NW China." Geological Magazine 152, no. 1 (2014): 41–69. http://dx.doi.org/10.1017/s0016756814000168.
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AbstractWe report two newly identified Ordovician ophiolite belts in west Junggar, NW China: Tajin–Tarbahatai–Kujibai–Honguleleng (TTKH) and Tangbale–Baijiantan–Baikouquan (TBB) ophiolitic belts. These two ophiolitic belts provide constraints for the Palaeozoic reconstruction of Central Asia and the geological evolution of this region. The TTKH and TBB ophiolitic belts are dismembered parts of different ophiolitic belts which represent relics of Ordovician oceanic floor; they subducted to the north under the Chingiz–Tarbahatai arc and to the south under the Junggar plate, respectively. The Baijiantan–Baikouquan ophiolite mélanges comprise the major part of the TBB. Flat rare Earth element (REE) patterns with positive Eu anomalies and insignificant depletion of high-field-strength elements (HFSE) relative to melts of primitive mantle suggest a mid-ocean-ridge basalt (MORB) origin for the metagabbro. Lherzolite samples define a Sm–Nd isotopic isochron with age of 474 Ma andɛNd(t)of +8.9. Lherzolite samples with positiveɛNd(t)values of +8.8 to +9.1 and initial87Sr/86Sr ratios of 0.7037–0.7040 are rather homogeneous in Sr–Nd isotopic composition, whereas metagabbro samples show wider Sr–Nd isotopic compositional ranges withɛNd(t)of +5.9 to +11.0. The Sm–Nd isotopic isochron age (c.380 Ma) for garnet amphibolite samples, consistent with a zircon U–Pb age (c.385 Ma) for metagabbro, represents a magmatic event prior to subduction. Thermodynamic calculations for garnet amphibolite yield a clockwise pressure–temperature path with peak metamorphic condition ofc.15 kbar and 520–560°C at 342 Ma, indicating a subduction-channel setting. The Rb–Sr isochron ages (335 Ma, 333 Ma) for metagabbro represent a metamorphic event during exhumation.
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IONOV, D. A. "Sr-Nd-Pb Isotopic Compositions of Peridotite Xenoliths from Spitsbergen: Numerical Modelling Indicates Sr-Nd Decoupling in the Mantle by Melt Percolation Metasomatism." Journal of Petrology 43, no. 12 (2002): 2261–78. http://dx.doi.org/10.1093/petrology/43.12.2261.
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