西藏拉萨地块北部申扎地区晚古生代—中生代地质演化

发布时间：2018-06-29 19:17

本文选题：拉萨地块 + 锆石年代学　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：本研究对拉萨地块北部申扎地区进行研究,通过野外调研,岩相学观察,Gazzi-Dickinson颗粒统计,锆石年代学研究,对研究区从晚古生代到中生代的若干地质问题形成新的认识。早白垩世的昂杰组砂岩中碎屑锆石年龄分布,以及岩相学研究结果,揭示了二叠纪时期拉萨地块应处于印度冈瓦纳北缘,接受特提斯域的物质沉积。拉萨地块北部三叠系沉积范围很小。研究区内的晚三叠世多布日组的碎屑锆石年龄分布与拉萨地块中北部的古生代地层的锆石年龄分布相似。结合岩相学颗粒统计结果,认为其物源主要为古生代地层的再旋回物质,很少有北部羌塘地块和拉萨地块南部的二叠纪-三叠纪时期的松多造山带和岩浆活动的物质。永珠蛇绿岩带属于狮泉河-永珠-纳木错蛇绿岩带的一部分。认为其代表一个拉萨地块内部的缝合带,是一系列弧后或弧间洋盆的残余。永珠蛇绿岩的席状岩墙群中一个辉长岩样品27个测点得到平均年龄153±2.3 Ma,指示申扎地区这一洋盆在晚侏罗世时期还没有闭合。申扎地区晚侏罗-早白垩时期的日拉组沉积覆盖在永珠蛇绿岩之上,沉积过程有受到断层活动影响的迹象。早白垩世时期,研究区有很多岩浆活动。区内采集的钾长花岗岩,安山玢岩,花岗斑岩,以及白垩系中的火山岩样品的锆石U-Pb定年结果显示它们都具有早白垩世年龄。它们应该与拉萨地块北部普遍发育的早白垩世岩浆活动具有相同的成因背景。申扎地区沿着狮泉河-纳木错混杂岩带,发育有很多自南向北逆冲为主的断层,它们将南部的古生代地层以及蛇绿岩逆冲到北部的白垩系之上。通过野外构造关系,年代学研究,沉积盆地物源分析,结合相邻区域的40Ar-39Ar热年代学研究的报道,本研究认为它们的活动最早开始于早白垩世早期,并持续作用到晚白垩世。这一断层系统北部的早白垩世砂岩的碎屑锆石年龄分布指示它们的物源主要为断层系统南部的古生代地层再旋回物质,以及拉萨地块北部的岩浆活动物质。这一沉积过程可能受到申扎地区断层系统的控制。本研究提出申扎地区的格仁错-纳木错逆冲断层系统是沿着狮泉河-纳木错混杂岩带代表的先存的构造薄弱带发育,它形成于北部拉萨-羌塘碰撞和南部可能存在的新特提斯洋向北平板俯冲的大地构造背景中。
[Abstract]:In this study, the study of Xainza area in the northern part of Lhasa block, through field investigation, petrographic observation, Gazzi-Dickinson particle statistics and zircon geochronology, a new understanding of some geological problems from Late Palaeozoic to Mesozoic in the study area. The age distribution of detrital zircons in the sandstone of the early Cretaceous Angjie formation and petrographic study It is revealed that the Lhasa massif in the Permian period should be in the northern margin of the Gondwana, India, to accept the material deposits in the Tethys domain. The sedimentary range of the Triassic in the northern part of the Lhasa massif is very small. The age distribution of the detrital zircons in the late three fold group of the study area is similar to the zircon age distribution of the Paleozoic strata in the northern part of the Lhasa massif. According to the statistical results of the phase, it is believed that its source is mainly a re cyclic substance in the Paleozoic strata, and there are few substances in the northern Qiangtang block and the southern part of the Lhasa massif in the Permian Triassic period of the pine multi orogenic belt and magmatism. The suture zone within the Lhasa massif is a series of remnants of the post arc or interarc oceanic basin. The average age of 27 samples of a gabbro sample in the permanent ophiolite group was 153 + 2.3 Ma, indicating that the Xainza basin was not closed during the late Jurassic period. The late Jurassic and Cretaceous period of the Xainza region was deposited in the Naga group. The deposition process is above the perpetual ophiolite, and the deposition process has a sign of the influence of fault activity. In the early Cretaceous period, there were many magmatic activities in the study area. The U-Pb dating results of the zircon from the samples collected in the region and in the volcanic rocks in the Cretaceous show that they all have early Cretaceous age. They should be in the early Cretaceous age. The early Cretaceous magmatic activity, which is widely developed in the northern part of the Lhasa massif, has the same genetic background. The Xainza area along the Shiquan River Nam Co melange belt developed many faults mainly from the south to the north. They thrust the Paleozoic strata in the South and the ophiolites back to the northern Cretaceous system. The study, the source analysis of sedimentary basins, and the report on the 40Ar-39Ar thermal chronology of adjacent regions, this study believed that their activities first began in the early Cretaceous and continued to be in the late Cretaceous. The age distribution of the detrital zircon of the early Cretaceous sandstone in the northern part of the fault system indicates that their source is mainly a fault. The Paleozoic stratigraphic re gyratory substance in the southern part of the system and the magmatic activity in the northern part of the Lhasa massif may be controlled by the fault system in the Xainza region. This study suggests that the Xainza area's green fault Nam Co thrust fault system is the first deposited weak tectonic belt represented by the Shiquan River Nam Co melange belt. It was formed in the tectonic setting of the collision between the northern Lhasa Qiangtang and the north facing subduction of the new Tethyan ocean in the south.
【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】：P534;P548

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