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Zhang D.Y.,Hefei University of Technology | Zhang D.Y.,Xinjiang Institute of Ecology and Geography | Zhou T.F.,Hefei University of Technology | Yuan F.,Hefei University of Technology | And 5 more authors.
Acta Petrologica Sinica | Year: 2015

The Sawuer area is located in the north part of the West Junggar region, which is characterized by the outcrops of the Devonian-Carboniferous pyroclastic sedimentary strata. In this study, the authors focused on the basaltic andesite from Tiepuke district, Southwest Sawuer area. The basaltic andesite strata are E-W trending, and there are some post-volcanism granite porphyry intruding nto the basaltic andesite strata. After detailed geological mapping, the basaltic andesite was dated as 427.6 ± 4.2 Ma with the LA-ICPMS U-Pb dating method, and the granite porphyry inserting in the Tiepuke basaltic andesite strata intruded at 387.2 ± 2.9 Ma. The dating results suggest that basaltic andesite from Tiepuke district was erupted is Early Paleozoic magmatism. This is the first time to report the discovery of the Early Paleozoic magmatism in the Sawuer area, which change the traditional understanding that there is no Early Paleozoic magmatism in Sawuer area. The basaltic andesite from Tiepuke district, comparing with the spatial and temporal distribution characters of the magmatism from the adjacent Tarbaghatai and Xiemisitai area, indicate that the Early Paleozoic magmatism in Sawuer may formed in the consistent background within Tarbaghatai-Sawuer-Xiemisitai setting, Northewest Junggar area. Source

Zhang H.,University of Science and Technology Beijing | Xu J.,University of Science and Technology Beijing | Cheng X.,University of Science and Technology Beijing | Guo X.,No. 706 Geological Party | And 3 more authors.
Acta Geologica Sinica | Year: 2015

The Talate Pb-Zn deposit, located in the east of the NW-SE extending Devonian Kelan volcanic-sedimentary basin of the southern Altaides, occurs in the metamorphic rock series of the upper second lithological section of the lower Devonian lower Kangbutiebao Formation (D1k1 2). The Pb-Zn orebodies are stratiform and overprinted by late sulfide-quartz veins. Two distinct mineralization periods were identified: a submarine volcanic sedimentary exhalation period and a metamorphic hydrothermal mineralization period. The metamorphic overprinting period can be further divided into two stages: an early stage characterized by bedding-parallel lentoid quartz veins developed in the chlorite schist and leptite of the ore-bearing horizon, and a late stage represented by pyrite-chalcopyrite-quartz veins crosscutting chlorite schist and leptite or the massive Pb-Zn ores. Fluid inclusions in the early metamorphic quartz veins are mainly CO2-H2O-NaCl and carbonic (CO2±CH4±N2) inclusions with minor aqueous inclusions. The CO2-H2O-NaCl inclusions have homogenization temperatures of 294-368° C, Tm,CO2 of -62.6 to -60.5°C, Th,CO2 of 7.7 to 29.6°C (homogenized into liquid), and salinities of 5.5-7.4 wt% NaCl eqv. The carbonic inclusions have Tm,CO2 of -60.1 to -58.5°C, and Th, CO2 of -4.2 to 20.6°C. Fluid inclusions in late sulfide quartz veins are also dominated by CO2-H2O-NaCl and CO2±CH4 inclusions. The CO2-H2O-NaCl inclusions have Th,tot of 142 to 360°C, Tm,CO2 of -66.0 to -56.6°C, Th,CO2 of -6.0 to 29.4°C (homogenized into liquid) and salinities of 2.4-16.5 wt% NaCl eqv. The carbonic inclusions have Tm, CO2 of -61.5 to -57.3°C, and Th, CO2 of -27.0 to 28.7°C. The aqueous inclusions (L-V) have Tm,ice of -9.8 to -1.3°C and Th,tot of 205 to 412°C. The P-T trapping conditions of CO2-rich fluid inclusions (100-370 MPa, 250-368°C) are comparable with the late- to post-regional metamorphism conditions. The CO2-rich fluids, possibly derived from regional metamorphism, were involved in the reworking and metal enrichment of the primary ores. Based on these results, the Talate Pb-Zn deposit is classified as a VMS deposit modified by metamorphic fluids. The massive Pb-Zn ores with banded and breccia structures were developed in the early period of submarine volcanic sedimentary exhalation associated with an extensional subduction-related back-arc basin, and the quartz veins bearing polymetallic sulfides were formed in the late period of metamorphic hydrothermal superimposition related to the Permian-Triassic continental collision. © 2015 Geological Society of China. Source

Geng X.X.,Chinese Academy of Geological Sciences | Chai F.M.,Xinjiang University | Yang F.Q.,Chinese Academy of Geological Sciences | Zuo W.Z.,Polytechnic University of Mozambique | And 3 more authors.
Acta Petrologica Sinica | Year: 2010

LA-ICP-MS U-Pb zircon ages are reported fo mela-rhyolites in the bimodal volcanic rocks from the Altaizhen Formation in Dalawuzi area at the southern margin of Altay orogenic belt. The zircons with well-defined oscillatory zoning from meta-rhyolite sample yielded mean 206Pb/238U ages of 365.6 ± 1.6Ma and 413.5 ± 2.0Ma. The age of 365.6 ± 1.6Ma represent the eruption age of the volcanic rocks of the Altaizhen Formation, which indicated that the Altaizhen Formation was formed during the Middle to Fate Devonian. The age of 413.5 ± 2.0Ma, which are consistent with the eruption age of the Kangbuliebao silicic volcanic rocks and Early Devonian granite, can be inteipreted as an age of captured zircon from Early Devonian magmatism. Geochemically, meta-basalts are rich in titanium, alkali (especially sodium), iron, LILE and LREE and poor in magnesium. They have higher contents of HIFSEs (Nb, Ta, Zr and Hf) than those of typical IAB. Meta-rhyolites are generally characterized by rich silicon, alkali, and poor magnesium. They have relatively high U, Th and rather low Ba, Sr, Ti and P. They display obvious negative anomaly of Nb, Ta and Ti, obvious enrichment of LREE, noticeable negative Eu anomalies (δEu =0.21 ~ 0.41). Basaltic and rhyolilic rocks show similar Pb isotopic data to M-MORB. On the basis of regional geological and geochemical evidences, this paper concludes that the basalt was originated from depleted asthenosphere and subducted material (subducted slab, sediments and fluids), and rhyolite resulted from thermal and the new accretion materials and mingling between basaltic magma and felsic magma. The bimodal volcanic rocks are the products of partial extension after the subduction. Source

Deng Y.-F.,Hefei University of Technology | Deng Y.-F.,Xinjiang Institute of Ecology and Geography | Yuan F.,Hefei University of Technology | Yuan F.,Xinjiang Institute of Ecology and Geography | And 7 more authors.
Journal of Asian Earth Sciences | Year: 2015

New U-Pb zircon ages and geochemical data including whole rock major and trace element concentrations, PGE and radiogenic isotopes are used to investigate the magma evolution processes and the sulfide saturation history of the Ural-Alaskan type Tuerkubantao mafic-ultramafic intrusion in southern Altai orogen. The Tuerkubantao intrusion consists of dunite, wehrlite, olivine pyroxenite, gabbro and diorite. Igneous zircons from a gabbro in the intrusion yielded a LA-ICP-MS U-Pb age of 370.3±4.8Ma, indicating that the intrusion was emplaced in the Late Devonian. The intrusive rocks are characterized by enrichment of large ion lithophile elements and depleted high field strength elements relative to N-MORB, which is similar to the Devonian Ural-Alaskan type intrusions in southern Altai orogen and different from Devonian volcanic rocks from ophiolites in West Junggar. The Tuerkubantao intrusive rocks have restricted (87Sr/86Sr)t ratios (0.70396-0.70453) and a large range of εNd(t) (-2.84 to +3.80). The trace elements and isotope compositions are comparable with those of the volcanic rocks along the Pacific margins of the Americas. The calculated parental magma of the Tuerkubantao rocks has a high-Mg basaltic composition with ~9.12wt% MgO and ~7.02wt% FeOT. It is proposed that the primary magma was generated from partial melting of metasomatized lithospheric mantle triggered by upwelling of asthenosphere at an active continental margin. The Cu/Pd ratios in gabbros (9.26×105-32.8×105) are obviously higher than those of the wehrlites (1.18×104-1.95×104), indicating that gabbros in the intrusion have experienced sulfide segregation, whereas sulfide saturation did not occur in the wehrlites. © 2015 Elsevier Ltd. Source

Deng Y.F.,Hefei University of Technology | Zhou T.F.,Hefei University of Technology | Yuan F.,Hefei University of Technology | Du X.W.,No. 706 Geological Party | And 2 more authors.
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2015

The Sawuer region is located at the northeastern margin of the West Junggar, where the Late Paleozoic volcanic and intrusive rocks ( including a few mafic intrusive rocks) are widespread. The geochronology of these magmatic rocks has great significance to constrain the Carboniferous tectonic setting in the West Junggar. This paper discusses the tectonic setting and the genetic mechanism of the Keketuobie intrusion in the Sawuer region and provides the evidence to constrain the Carboniferous tectonic setting in the West Junggar based on the petrography, SHRIMP U-Pb ages of zircons and geochemical compositions of different rock types from the Keketuobie intrusion. The Keketuobie intrusion is made up of medium-coarse grained gabbro, fine grained gabbro and diorite. The veined fine grained gabbro intruded in the medium-coarse grained one and some medium-coarse grained gabbro inclusions occurred in the veined fine grained gabbro. The contact between the medium-coarse grained gabbro and diorite is gradational. These petrographic characteristics indicate that the Keketuobie intrusion was formed from multiple pulses of magma. The early magma formed the medium-coarse grained gabbro and diorite, the later magma emplaced in tectonic fractures of the medium-coarse grained gabbro and formed veined fine grained one. According to SHRIMP U-Pb age analysis results, the crystallization of the fine grained gabbro is 323.2 ± 6.2Ma, corresponding to late Early Carboniferous. The diagenetic age of the Keketuobie intrusion is older than those of ophiolite rocks, island arc volcanic rocks, the intrusive rocks in the porphyry deposits, coeval with the ages of the I-type granites, but clearly earlier than those of the post-collision A-type granites and bimodal volcanic rocks, suggesting the Keketuobie intrusion may be formed in the syn-collosional environment. The correlation of major oxides and the similar trace element partitions of the different rocks suggest that they are resulted from crystallization differentiation of the same primary magma. The petrographic and geochemical features suggest primary magma of the intrusion was produced by interactions between depleted asthenospheric melts and metasomatized lithospheric mantle. The slab break-off might play an important role in the upwelling of asthenospheric mantle. Source

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