Provenance of the Triassic Songpan–Ganzi flysch, west China
Provenance of the Triassic Songpan–Ganzi flysch, west China
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DOI：
10.1016/j.chemgeo.2006.01.001
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发表时间：
2006-07
期刊：
影响因子：
3.9
通讯作者：
Zhenbing She;Changqian Ma;R. Mason;Jian-wei Li;Guocan Wang;Yuhong Lei
中科院分区：
文献类型：
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作者：
Zhenbing She;Changqian Ma;R. Mason;Jian-wei Li;Guocan Wang;Yuhong Lei
中国西部松潘—甘孜盆地是青藏高原东北角的一个三角形构造，充满了厚厚的三叠纪复理石，北边是东昆仑造山带，向东延伸为秦岭—大别带，西南边是甘孜—理塘蛇绿岩和义敦火山弧，西边是甘孜—理塘蛇绿岩和义敦火山弧。 东临龙门山冲断带。我们对松潘—甘孜盆地北侧巴里安哈尔地区典型浊积岩开展了迄今为止最广泛的岩石学和地球化学研究，包括常量元素、微量元素、Rb/Sr和Sm/Nd同位素分析。岩相学研究确定砂岩为典型的杂砂岩，其基质为细粒碎屑物质，经绿片岩相变质作用重结晶。化学风化指数证实，细粒浊积岩在运输和沉积过程中几乎没有改变，因此成分准确地代表了其来源区域。各种判别图上显示的主量、痕量和同位素分析表明，巴里安哈拉地区的复理石源自东昆仑带北部，这一结论得到了已发表的古水流方向的支持。将巴彦喀拉浊积岩与松潘-甘孜盆地东侧川西地区已发表的结果进行比较表明，后者源自多种沉积岩和少量火成岩的源区。最有可能的来源是东北部的南秦岭。目前的数据不支持松潘-甘孜盆地的物质源自义敦火山弧或大别超高压变质带。目前对三叠纪松潘-甘孜复理石的物源研究支持了古特提斯洋向西打开的模式，并揭示了祁连-秦岭-大别造山带和东昆仑造山带的不同演化历史。
The Songpan–Ganzi Basin of western China is a triangular structure on the northeast corner of the Qinghai–Tibet Plateau filled with a great thickness of Triassic flysch, surrounded to the north by the Eastern Kunlun Orogenic Belt that extends farther eastwards as the Qinling–Dabie Belt, to the southwest by the Ganzi–Litang Ophiolite and Yidun Volcanic Arc and to the east by the Longmenshan Thrust Belt. We have carried out the most extensive petrographic and geochemical study so far undertaken on typical turbidites from the Songpan–Ganzi Basin including major element, trace element, Rb/Sr and Sm/Nd isotopic analyses in the Baryan Har region on the northern side of the basin. Petrographic study identifies the sandstones as typical graywackes whose matrix is fine-grained detrital material, recrystallized by greenschist facies metamorphism. Chemical weathering indices confirm that the fine-grained turbidites were little altered during transport and deposition, so compositions accurately represent their source areas. Major, trace and isotope analyses displayed on various discriminant diagrams indicate that the flysch from the Baryan Har region is derived from the Eastern Kunlun Belt to the north, a conclusion supported by published paleocurrent directions. Comparison of the Baryan Har turbidites with published results from Western Sichuan on the eastern side of the Songpan–Ganzi Basin suggests that the latter is derived from a source area of varied sedimentary rocks and a few igneous rocks. The most likely source is South Qinling to the northeast. Presently available data do not support derivation of material in the Songpan–Ganzi Basin from the Yidun Volcanic Arc or the Dabie Ultra-High Pressure Metamorphic Belt. The present provenance studies on the Triassic Songpan–Ganzi flysch support a westward opening model for the Paleotethyan Ocean and reveal different evolutional histories for the Qilian–Qinling–Dabie and Eastern Kunlun Orogens.