西藏改则热那错地区中酸性侵入岩岩石地球化学特征及形成背景

发布时间：2018-04-18 19:17

本文选题：西藏改则热那错 + 班怒带　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：西藏地区历来都是全球地质工作者的热点研究区域,本论文研究区大地构造位置位于班公湖-怒江缝合带与龙木错-双湖逢合带之间。研究区内的构造演化受到班公湖-怒江缝合带的控制。但在大地构造背景上还存在许多争议。有的学者认为班怒洋壳向北俯冲至羌塘陆块之下;有的学者认为是班怒洋壳向南俯冲至拉萨地块之下;还有学者认为班公湖中特提斯洋壳向北、向南作双向俯冲。研究区内出露一套侵入岩,其岩性组合为云英闪长岩,石英二长闪长岩,石英闪长岩,花岗闪长岩。主量元素特征显示为一套中酸性侵入岩,为高钾钙碱性准铝质I型花岗岩,Harker图解显示有很好线性相关性。稀土配分曲线向右倾斜,具有弱的负铕异常,是LREE相对富集,而HREE相对亏损,都属轻稀土富集类型。微量元素原始地幔标准化蜘蛛图表现为整体上向右倾斜,强不相容的元素较为富集,高场强的元素Ta、Nb、Ti负异常明显。锆石U-Pb的SHRIMP测年结果为:石英二长闪长岩为139±4Ma,MSWD=1.6;石英闪长岩为147.3±3.3Ma,MSWD=0.45,花岗闪长岩为134±4Ma,MSWD=5.6,形成时代均为晚侏罗世-早白垩世早期。结合研究区的大地构造位置,与采集样品的地球化学分与年龄分析结果,认为改则县北的侵入岩为班公湖-怒江洋向北俯冲时期形成的火山弧花岗岩,其特征为高钾的准铝质钙碱性I型花岗岩,是同源演化的产物,其物质来源为壳幔混合来源,且源区受到来自俯冲板块的沉积物熔体的交代。根据本次测年结果,结合研究区内的沉积及构造特征,判断班怒洋洋壳于晚侏罗世向北俯冲。
[Abstract]:Tibet has always been a hot research area for geologists all over the world. The tectonic location of the study area lies between the Bangong Lake-Nujiang suture zone and the Longmu-Shuanghu-Shuanghu suture zone.The tectonic evolution in the study area is controlled by the Bangong Lake-Nujiang suture zone.However, there are still many controversies in the tectonic background.Some scholars think that the Banrou oceanic crust subducts to the north under the Qiangtang block; some scholars think that the Banrou oceanic crust subducts south to the Lhasa block; others believe that the Tethys oceanic crust in Bangong Lake subducts north and makes a two-way subduction south.A set of intrusive rocks are exposed in the study area. Their lithologic assemblages are Yunying diorite, quartz diorite, quartz diorite and granodiorite.The principal element features are a set of intermediate-acid intrusive rocks, and the Harker diagram of high-potassium calc-alkaline quasi-alumintic I-type granite shows a good linear correlation.The rare earth partition curve inclines to the right and has weak negative europium anomaly, which is relatively enriched in LREE, and HREE is relatively depleted, which all belong to the type of light rare earth enrichment.The trace element primitive mantle-standardized spider map shows that the whole is inclined to the right, the strongly incompatible elements are more enriched, and the high field strength element Taan NbCTi is negative anomaly obviously.The SHRIMP dating results of zircon U-Pb are as follows: the quartz diorite is 139 卤4 Ma-MSWD1.6, the quartz diorite is 147.3 卤3.3 Ma-MSWDU 0.45, and the granodiorite is 134 卤4 Ma-MSWD5. 6. The age of formation is from late Jurassic to early Cretaceous.In combination with the geotectonic location of the study area and the geochemical score and age analysis of the collected samples, it is considered that the intrusive rocks in the north of the county are volcanic arc granites formed during the northward subduction of the Bangonghu Lake and the Nujiang Ocean.It is characterized by a high-potassium quasi-aluminous calc-alkaline I-type granite, which is the product of homologous evolution. Its material source is a mixture of crust and mantle, and the source region is metasomatized by the sediment melt from subduction plate.According to the results of this dating, combined with the sedimentary and structural characteristics of the study area, it is concluded that the Banrou oceanic crust subducted northward in the late Jurassic.
【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】：P588.121

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