东昆仑东段布青山地区上二叠统格曲组物源分析及其构造意义

Provenance analysis and structural implications of Gequ Formation at the Buqingshan area in the eastern segment of the East Kunlun region

对东昆仑东段布青山得力斯坦地区出露的上二叠统格曲组砾岩层进行砾石成分、砾度统计及系统的LA-ICP-MS锆石UPb年龄谱分析。结果表明,格曲组砾岩层砾石成分以石英岩和花岗岩为主,硅质岩和基性岩次之,砂岩和灰岩较少,砾石的分散系数为1.54~2.02,该套砾岩为近源快速堆积的产物。砾岩碎屑锆石U-Pb年龄可分为3组：1早奥陶世—晚志留世年龄组为499~409Ma,峰值年龄为426Ma,对应早古生代末期原特提斯洋向北俯冲碰撞产生的一系列构造岩浆事件;2新元古代年龄组为744~619Ma,峰值年龄为744Ma,对应于全球Rodinia超大陆裂解事件;3古元古代年龄组为2443Ma,对应东昆仑地区古元古代构造岩浆热事件。结合碎屑锆石年龄及沉积学特征综合分析,花岗质砾石来源于北侧东昆仑造山带加里东期岩浆弧,沉积岩砾石则可能来自造山带早期的沉积地层,石英岩及其他变质岩砾石则多来自东昆仑基底变质岩系。综合判别,格曲组为一套沉积于活动大陆边缘环境的滨浅海相磨拉石建造,代表南侧古特提斯洋向北俯冲开始的构造阶段,是初始俯冲的沉积构造响应。

Detailed statistics of gravel composition, gravel granulometry and the LA-ICP-MS U-Pb dating of detrital zircons from conglomerate bed in Delisitan of Buqingshan show that this conglomerate was derived from the nearby place with rapid accumulation. This conglomerate consists mainly of quartzite and granite and subordinately of siliceous rocks and basic rocks, with minor sandstone and limestone. The coefficients of dispersion are 1.54~2.02 for the gravel of conglomerate. The detrital zircon age spectra can be divided into three groups：1Early Ordovician-Late Silurian age group, 499~409Ma, with the peak value being 426 Ma, corresponding to the tectono-magmatic events associated with Proto-Tethys northward subduction and collision at the end of Early Paleozoic; 2Neoproterozoic age group, 744~619Ma, with the peak value being 744 Ma, corresponding to the breakup of Rodinia supercontinent; 3Paleoproterozoic age group, 2443 Ma, corresponding to the tectono-magmatic hydrothermal event of East Kunlunin Paleoproterozoic. An integrated analysis of the U-Pb detrital zircon ages and sedimentology characteristics show that the granite gravel was derived from magmatic arc in Caledonian in northern East Kunlun Orogen, the gravel of quartzite and metamorphic rocks was from the East Kunlun metamorphic rock series in basement, and the gravel of sedimentary rocks might have come from the early sedimentary formation in the orogenic belt. A comprehensive analysis reveals that the Gequ Formation is a mollasse formation of the littoral-shallow facie which deposited on anactive continental margin. It represents both the beginning of the Paleo-Tethys northward subduction and the sedimentary responding of tectonics at the beginning of the subduction.