Neoproterozoic ultramafic–mafic-carbonatite complex and granitoids in Quruqtagh of northeastern Tarim Block,western China: Geochronology,geochemistry and tectonic implications |
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| Institution: | 1. Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing 100037, China;2. Institut für Geowissenschaften, Universität Mainz, D-55099 Mainz, Germany;3. Institute of Earth Sciences, Taiwan National University, Nangang, Taipei 11529, Taiwan;4. National 305 Project Office, Western Kelamayi Road 2, Urumqi, China |
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| Abstract: | U–Pb zircon and baddeleyite ages, and geochemical and Nd isotopic data, are reported for a ultramafic–mafic-carbonatite complex and granites in Quruqtagh of northeastern Tarim Block, NW China. The carbonatite and plagioclase-bearing pyroxenite from the Qiganbulake mafic–ultramafic-carbonatite ring complex (QMC), the Xingdi granodiorite and the Taiyangdao granite were emplaced at 810 ± 6, 818 ± 11, 820 ± 10 and 795 ± 10 Ma (95% confidence level), respectively. The QMC is composed of dunite, apatite- and/or feldspar-bearing pyroxenite, pyroxenite, phlogopitelite and carbonatite. Petrography, geochemistry and mineral chemistry suggest that the QMC rocks were generated by partial melting of a CO2-metasomatized mantle in a rifting environment. The Xingdi and Taiyangdao granitoids possess high LREE, Na2O/K2O, Sr/Y, (La/Yb)N ratios and low HREE and HFSE contents, similar to modern adakites. However, they have lower MgO (or Mg#), Cr and Ni contents and unradiogenic Nd isotopes (pronounced negative ?Nd(t) value of ?12.7 to ?17.3 and Neoarchaean Nd model ages) than slab-derived adakites. Thus, they were likely formed by partial melting of Neoarchaean mafic protoliths in the lower crust, leaving behind a granulite residue. The QMC and the granitoids in Quruqtagh constitute a bimodal intrusive suite in a Neoproterozoic continental rift setting, possibly related to mantle plume activities beneath the Rodinian supercontinent. |
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