青藏高原羌塘中部下石炭统日湾茶卡组的物源分析及构造属性探讨

发布时间：2018-03-03 18:36

本文选题：青藏高原　切入点：羌塘中部　出处：《吉林大学》2015年硕士论文　论文类型：学位论文

【摘要】：羌塘地块处于青藏高原中北部，龙木错－双湖－澜沧江板块缝合带将其划分为羌南和羌北两大块体，羌南具有亲冈瓦纳大陆的特点，而羌北具有亲欧亚大陆的特点。两侧的基底性质与构成、古生代沉积建造和生物地理区系、岩浆活动与变质作用、构造运动分期存在着显著差异。近年来龙木错－双湖－澜沧江板块缝合带研究取得了突破性进展，许多关键地质问题集中在羌塘地区，无人区的神秘面纱逐渐被揭开，李才教授将其比喻为打开青藏高原地学皇冠上的明珠。在龙木错－双湖－澜沧江板块缝合带中段的冈玛错－日湾茶卡地区，近东西向展布着一条富含暖水型生物化石的早石炭世地层－日湾茶卡组（C1r），出露面积约100平方公里。日湾茶卡组是羌塘中部少有的具有化石时代依据的沉积地层，且含有扬子型Guizhouphyllum－Yuanophyllum珊瑚等化石组合，一直是众多学者关注的热点。然而由于其位处羌塘无人区，条件极其艰苦，淡水缺乏，无道路通行，其研究程度并不高。近年来我们发现日湾茶卡组南北两侧均分布着典型的冈瓦纳相冷水型沉积地层－展金组（C2P1z），二者呈构造接触。含有扬子型生物化石的暖水型沉积夹持于典型的冈瓦纳相冷水型沉积之中，这一特殊地质现象的解答对该区乃至整个龙木错－双湖－澜沧江板块缝合带的演化具有重要意义。本文在大量野外工作的基础之上，充分利用前人的研究资料和成果，，综合运用岩石学、同位素年代学及构造地质学等多学科知识对日湾茶卡组进行了全方位研究。日湾茶卡组砂岩和砾岩样品LA－ICP－MS锆石U-Pb测年分析结果存在325～400M（a主要峰值为360Ma），400～500Ma（峰值为437和454Ma），500～600Ma（极少），800～1100Ma和1200Ma五个年龄区间。最年轻碎屑锆石年龄在320Ma左右，与古生物化石组合反映时代一致，印证了其时代为早石炭世维宪期；碎屑锆石中360Ma、437Ma、454Ma年龄峰值最为明显，为龙木错－双湖－澜沧江洋岛弧消减事件和加里东运动的年龄记录，表明碎屑岩的物源区主要来自扬子大陆周缘。结合古生物化石资料可知，日湾茶卡组属于欧亚大陆扬子型石炭纪沉积地层，为岛弧环境下的一套浅水台型沉积。
[Abstract]:The Qiangtang block is located in the central and northern part of the Qinghai-Xizang Plateau, and the Longmu-Shuanghu-Lancangjiang plate suture zone divides it into two blocks: the southern Qiang and the northern Qiang. The southern Qiang is characterized by a pro-Gondwana continent. On the other hand, the north of Qiang Dynasty has the characteristics of being pro-Eurasian, the properties and composition of the basement on both sides, the Paleozoic sedimentary formation and biogeographic fauna, magmatic activity and metamorphism. In recent years, great progress has been made in the study of the suture zone of the Longmu-Shuanghu-Lancang River plate. Many key geological problems are concentrated in the Qiangtang area, and the mysterious veil of the no-man 's land has been gradually unravelled. Professor Li Cai likened it to opening the crown of the Qinghai-Xizang Plateau. In the Gangma Chaka area of the middle section of the Longmu-Shuanghu-Lancang River plate suture zone, Near the east to west, there is an early Carboniferous strata rich in warm water type biofossils, the Jiwan Chaka formation, with a exposed area of about 100 square kilometers. The Riwan Chaka formation is one of the few sedimentary strata with fossil age basis in the middle of Qiangtang. The fossil assemblage containing Yangtze type Guizhouphyllum-Yuanophyllum coral has always been a hot topic for many scholars. However, due to its location in no man's land in Qiangtang, the conditions are extremely difficult, fresh water is scarce, and there is no road passage. In recent years, we have found that there are typical cold water sedimentary strata of Gondwana facies on the north and south sides of the Jiwan Chaka formation, and the two are tectonic contacts. Warm water sedimentation with Yangtze type biofossils is also found. Trapped in a typical Gondwana cold water deposit, The solution of this special geological phenomenon is of great significance to the evolution of the suture zone of the Longmujiao-Shuanghu-Lancang River plate in this area. On the basis of a great deal of field work, this paper makes full use of previous research materials and achievements, and synthetically applies petrology. Isotopic geochronology and tectonic geology were used to study the Jiwan Chaka formation in an all-round way. The LA-ICP-MS zircon U-Pb dating of sandstone and conglomerate samples of the Jiwan Chaka formation shows that the main peak value of zircon U-Pb dating is 360 Ma, 400 Ma, 500 Ma (the peak values are 437 and 454 Ma, 500600 Ma) (P < 0.05). Very few of the five ages range from 800 Ma to 1200 Ma. The youngest age of the clastic zircon is about 320 Ma. Consistent with the age of paleontological fossil assemblage, it is confirmed that its age is the early Carboniferous Shiwei constitutional period, and the peak age of 360 Ma, 437 Ma and 454 Ma in the zircon is the most obvious, which is the age record of the island arc subduction event and Caledonian movement in Longmu Duo-Shuangghuang-Lancangjiang Ocean. The results show that the source region of the clastic rocks is mainly from the margin of Yangtze continent. According to the paleontological fossil data, the Jiwan Chaka formation belongs to the Yangtze type Carboniferous sedimentary strata in Eurasia, which is a set of shallow water platform deposits under the island arc environment.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.45

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