西藏羌塘中部南羌塘增生杂岩沉积环境分析及大地构造意义

发布时间：2018-03-21 04:02

本文选题：羌塘　切入点：龙木错-双湖缝合带　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：研究区位于羌塘中部南羌塘的玛依岗日地区和雪水河地区,构造位置位于龙木错—双湖缝合带中段,主要地层为早古生代俄久卖岩组(E1-2),石炭—二叠系冈塘错岩组((C-P2)g)、石炭—二叠系雪水河岩群((C-P2)x)、中晚三叠统玛依岗日岩组(T2-3m)。本文对增生杂岩带内沉积地质体四条岩性剖面进行实测分析、并对玄武岩、砂岩采用岩石矿物学和地球化学等方法进行详细分析,结果表明:玛依岗日岩组和冈塘错岩组源岩沉积环境为海底扇沉积,雪水河岩群为半深海-深海相沉积,早古生代岩群俄久卖岩组为滨、浅海环境沉积。雪水河附近玄武岩Ti O2、P2O5含量高,稀土总量高,轻重稀土强烈分馏的特点,富集大离子亲石元素Ba、Rb和高场强元素Zr、Th、Hf,地球化学特征和稀土微量元素分布形式均与标准洋岛型玄武岩相似。地球化学判别图解显示为板内洋岛环境,岩浆上涌过程中受到了来自于地壳物质的混染,但混染程度不深。玛依岗日砂岩稀土元素总量较高,其稀土配分与Bhatia提出的大洋岛弧杂砂岩相近,明显的轻稀土富集特征,无明显的Eu负异常,不具有Ce异常,而不同于大陆岛弧和活动陆缘杂砂岩。在构造背景判别图解中,显示出物源构造背景相对比较复杂,大部分属于大洋岛弧环境,其次为大陆岛弧环境。通过对冈塘错岩组和玛依岗日岩组砂岩重矿物分析,其物源母岩可能是一个不稳定的造山带甚至为火山弧。通过增生杂岩带内的几个主要沉积地质体分析,并结合前人研究资料,增生杂岩带演化产物主要为:晚石炭世—早二叠世时期,堆晶辉长岩和二叠系的蛇绿岩即代表了古特提斯洋初始张开的产物;早二叠世,古特提斯洋开始俯冲,雪水河洋岛型玄武岩即是古特提斯洋俯冲消减的残余地质体;中晚三叠世时期,古特提斯洋已经开始发生俯冲消减,并伴随着变质岩和岛弧火山岩的形成,至晚三叠世中晚期,俯冲作用完成,古特提斯洋闭合,羌南和羌北两地块发生碰撞,形成了典型的造山带增生杂岩。
[Abstract]:The study area is located in the Maygang and Xueshui River areas in the southern Qiangtang area of the central Qiangtang, and the tectonic position is located in the middle section of the Longmujia-Shuanghu suture zone. The main strata are early Paleozoic E1-2G, Carboniferous-Permian Gangtang dislocation formation, Carboniferous-Permian Xueshuihe Group, Carboniferous-Permian Xueshuihe Group, Middle and late Triassic Mayigang Ri formation, T2-3m.The four lithologic profiles of sedimentary geological bodies in the accretive complex are presented in this paper. Surface measurement and analysis, The basalt and sandstone are analyzed in detail by means of petro-mineralogy and geochemistry. The results show that the source rock sedimentary environment of Mai Gangri formation and Gangtang fault rock formation is submarine fan deposition, and Xueshuihe rock group is semi-deep-sea and deep-marine sedimentary. The early Paleozoic Ejiushiyan formation is a shoreline and shallow sea sedimentary environment. The basalt near Xueshui River is characterized by high content of TIO _ 2O _ 2P _ 2O _ 5, high amount of rare earth, and strong fractionation of heavy and heavy rare earths. The geochemical characteristics and the distribution of rare earth elements are similar to those of standard oceanic island basalts, and the geochemical discriminant diagram shows that the geochemical discriminant diagram is an intraplate oceanic island environment. In the process of magma upwelling, it was mixed by crustal materials, but the degree of mixed contamination was not deep. The total amount of rare earth elements in Mai Gangri sandstone is relatively high, its rare earth distribution is close to that of oceanic island arc complex sandstone proposed by Bhatia, and the enrichment characteristics of light rare earth elements are obvious. There is no obvious negative EU anomaly and no ce anomaly, which is different from continental island arc and active continental margin complex sandstone. In the distinguishing diagram of tectonic background, it shows that the provenance tectonic background is relatively complex, most of which belong to the oceanic island arc environment. Secondly, the continental island arc environment. Based on the analysis of sandstone heavy minerals in Gangtang fault rock formation and Mayiganri formation, The source rock may be an unstable orogenic belt or even a volcanic arc. The evolution products of the accretive complex are: during the late Carboniferous to early Permian, the heaped gabbro and the Permian ophiolite represented the initial opening of the PaleoTethys Ocean, and the PaleoTethys Ocean began to subduction in the early Permian. The islet basalt of Xueshuihe Ocean is the residual geological body of the subduction of the PaleoTethys ocean, which began to subduction in the middle and late Triassic, and was accompanied by the formation of metamorphic rocks and island arc volcanic rocks until the middle and late Triassic. The subduction was completed, the paleoTethys ocean was closed, and the southern Qiang and the northern Qiang landmasses collided, forming a typical orogenic belt accretive complex.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P512.2;P548

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