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Crystalline basement and Precambrian crustal growth of the continental massifs within the Central Asian Orogenic Belt (CAOB) are still pending problems. Our geological and geochemical investigations identified an Archean (2606 Ma) granitic pluton in the Biliya area of the Erguna Massif. The Neoarchean granitoids show high and positive in-situ zircon εHf(t) (+0.3 to +10.0), whole-rock εNd(t) (+4.8) and whole-rock εHf(t) values (+2.1). They are characterized by high Y + Ce + Zr + Nb (> 220 ppm) and Zr contents and could be classified as A-type granites. These granitoids are characterized by high Zr saturation temperatures (TZr) (796–836°C). They were derived from partial re-melting of juvenile mafic lower crust in an intracontinental back-arc extensional environment. This newly identified Neoarchean granitic pluton may represent the crystalline basement of the several continent massifs within the CAOB, and their high ?Hf(t)–?Nd(t) values may also indicate the occurrence of lateral crustal growth events in these massifs during the Neoarchean.  相似文献   

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Gossan Hill is an Archean (∼3.0 Ga) Cu–Zn–magnetite-rich volcanic-hosted massive sulfide (VHMS) deposit in the Yilgarn Craton of Western Australia. Massive sulfide and magnetite occur within a layered succession of tuffaceous, felsic volcaniclastic rocks of the Golden Grove Formation. The Gossan Hill deposit consists of two stratigraphically separate ore zones that are stratabound and interconnected by sulfide veins. Thickly developed massive sulfide and stockwork zones in the north of the deposit are interpreted to represent a feeder zone. The deposit is broadly zoned from a Cu–Fe-rich lower ore zone, upwards through Cu–Zn to Zn–Ag–Au–Pb enrichment in the upper ore zone. New sulfur isotope studies at the Gossan Hill deposit indicate that the variation is wider than previously reported, with sulfide δ34S values varying between −1.6 and 7.8‰ with an average of 2.1 ± 1.4‰ (1σ error). Sulfur isotope values have a broad systematic stratigraphic increase of approximately 1.2‰ from the base to the top of the deposit. This variation in sulfur isotope values is significant in view of typical narrow ranges for Archean VHMS deposits. Copper-rich sulfides in the lower ore zone have a narrower range (δ34S values of −1.6 to 3.4‰, average ∼1.6 ± 0.9‰) than sulfides in the upper ore zone. The lower ore zone is interpreted to have formed from a relatively uniform reduced sulfur source dominated by leached igneous rock sulfur and minor magmatic sulfur. Towards the upper Zn-rich ore zone, an overall increase in δ34S values is accompanied by a wider range of δ34S values, with the greatest variation occurring in massive pyrite at the southern margin of the upper ore zone (−1.0 to 7.8‰). The higher average δ34S values (2.8 ± 2.1‰) and their wider range are explained by mixing of hydrothermal fluids containing leached igneous rock sulfur with Archean seawater (δ34S values of 2 to 3‰) near the paleoseafloor. The widest range of δ34S values at the southern margin of the deposit occurs away from the feeder zone and is attributed to greater seawater mixing away from the central upflow zone. Received: 10 June 1999 / Accepted: 28 December 1999  相似文献   

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The formation ages of global magmatic sulfide Ni-Cu deposits are from Archean to Mesozoic,the Neoarchean and Neoproterozoic are the two peaks.In China,the formation ages of magmatic sulfide deposits are from Proterozoic to Mesozoic,and the Neoproterozoic and late Paleozoic are the two peaks,.Compared with the global magmatic deposits,there is no case study of the Archean magmatic Ni-Cu sulfide deposits in China before.The nickel deposits formed in Neoproterozoic are located on the margin of the North China Block and Yangtze Block(e.g.Jinchuan,Dapoling),and those formed in the late Paleozoic are mainly distributed in the Central Asian Orogenic Belt(CAOB).Emeishan and Tarim Large Igneous Provinces(LIPs).such as Kalatongke,Yangliuping,and Pobei.  相似文献   

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High-pressuremetamorphiceclogite,asawindowofstudyfordepthleveloflowermostcrustandmantle,hasanimportantindicatingsignificancet...  相似文献   

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1 Introduction With a wide distribution of the early Precambrian rocks, eastern Hebei Province is one of the classical regions for early Precambrian study of China. From the 1960s up to now, a great deal of geological surveys and researches have been undertaken in the region. The region was well-known among geologists of the world for the first report of the isotopic age of c. 3500 Ma (Rb-Sr Group, Laboratory of Isotopic Geology and Composite Research Group, Institute of Geology, Academ…  相似文献   

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