New Advance in Oceanic Island Basalts of Ophiolitic Mélange from the West Junggar
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    Abstract:

    Ocean island basalt (OIB) is one of fundamental issues in the study of petrology and geochemistry of solid Earth at present, itoccurs in many ophiolitic mélange belts and accretionary complexes, and it was usually considered driving from the plume. The West Junggar region is located in the southwestern part of the Central Asian Orogenic Belt (CAOB) which is situated among the Siberia, East European, Tarim and North China cratons. The geology of this region is characterized by widespread development of Late Carboniferous–Permian granitoids and Paleozoic ophiolitic mélanges, including Tangbale, Mayile, Darbut and Karamay ophiolitic mélanges. They are similar in composition with serpentinite, serpentinized harzburgite, lherzolite, dunite, chromite, pyroxenite, gabbro, diabase, basalt (tholeiitic and alkaline), chert and plagiogranite. With the deepening of the study, the OIBs with different ages have been identified in ophiolitic mélanges (Tangbale, Mayile, Darbut and Karamay) from the West Junggar. Geochemically, the basalts from ophiolitic mélanges are alkaline basalt series, characterized by high TiO2 and FeOt, low MgO, strongly LREE enrichment, and no obvious Nb, Ta negative anomalies. This is very similar to oceanic island basalts from Xigaze and Hawaii, which are probably formed in the ocean seamount and/or oceanic plateaus in oceanic plate. The alkaline basalts were derived from mantle plume-related source, indicating that not only the intra-oceanic subduction system but also mantle plume activity in the West Junggar (ocean) evolution. Combining with previous studies, we suggest that the CAOB may be intra-oceanic subduction with mantle plume compound evolution model. Furthermore, On the basis of the formed ages of OIB and OIB -type basalts in the CAOB, we found that they are not only having the large wide era, but also has a continuous developmental characteristics. If the plume model as proposed here is correct, this provides new information and evidence for correcty understanding the mantle plume activity contribution for crustal growth in CAOB at the Phanerozoic.

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YANG Gaoxue, LI Yongjun, TONG Lili, YANG Baokai, ZHANG Shenglong, SHEN Rui, DUAN Fenghao.2015. New Advance in Oceanic Island Basalts of Ophiolitic Mélange from the West Junggar[J]. Acta Geologica Sinica,89(2):392-405

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History
  • Received:May 08,2014
  • Revised:September 17,2014
  • Adopted:February 12,2015
  • Online: February 12,2015
  • Published: