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ASI-01 Geodynamic evolution of Asia
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SHRIMP zircon dating of the gabbro from the Kukejiliega ophiolite in the West Kunlun Mts. and its geological significance
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Jun Wang, Institute of Geology, Chinese Academy of Geological Sciences (China)
Qingguo Zhai, Institute of Geology, Chinese Academy of Geological Sciences (China)
Yong Wang, Institute of Geology, Chinese Academy of Geological Sciences (China)
Xuchang Xiao, Institute of Geology, Chinese Academy of Geological Sciences (China)
Jiangxin Yao, Institute of Geology, Chinese Academy of Geological Sciences (China)
Peisheng Bao, Institute of Geology, Chinese Academy of Geological Sciences (China)
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The ophiolite belt, which is mainly composed of Wuyitage ophiolite, Kegang ophiolite, Kudi ophiolite and Subashi ophiolite, distributed along the West Kunlun ¨C Karakorum orogen. Controversies on these ophiolites' ages and tectonic significance have existed among geologists. The Kukejiliega mafic-ultramafic block, which is about 27.3Km2,is one of dismembered blocks of the Kegang ophiolite. Another big mafic-ultramafic block of the Kegang ophiolite is the Katelieke block. The Kukejiliega ophiolite has undergone strong metamorphism. It is mainly composed of serpentinized dunite and harzburgite, meta pyroxenite, meta gabbro and meta basalt. The alteration products of gabbro are sericite, chlorite and epidote. Clear cumulate layers developed in the meta gabbro can be observed on the outcrops. The country rocks are mainly Ordovician meta clastics and carbonatites. Due to the hard nature conditions, few studies have been reported about this ophiolite. Geochemical analysis indicates it was formed in an island-arc tectonic environment. Zircons have been selected collected from the meta cumulate gabbro of the Kukejiliega ophiolite. The cathodoluminescence (CL) images of the zircons indicate they are of typical magmatic origin. Most grains have euhedral-subhedral shapes, and some of them with oscillatory zoning rims. The zircons were tested using SHRIMP II at the Beijing SHRIMP center. The dating results of the zircons suggest that gabbro in the Kukejiliega ophiolite was formed at 523±7Ma. The cumulate gabbros are usually considered to be the product of differentiation within ophiolites and also the differentiation products of a basaltic magma. Some age spots show discordant results, they are not included in calculating the age. The significance for these spots needs further studies. The Kudi ophiolite, located to the southeast of the Kegang ophiolite, which is a detailedly studied ophiolite in west China. Some geologists consider that it could be formed in Late Proterzoic to Early Paleozoic, while other geologists contend that it might be formed in Carboniferous. Recent studies on the SHRIMP U-Pb dating of the gabbro from the Kudi ophiolite show its ages of 510±4Ma (Xiao Xuchang et al., 2003) and 525±2.9Ma (Zhang Chuanlin et al., 2004). Comparing it with the Kudi ophiolite, we think the Kukejiliega ophiolite was formed at the same time with the Kudi ophiolite. They represent spreading to consumption of an oceanic basin on the northwest margin of Tibetan plateau during the Neoproterozoic-Early Paleozoic.
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