拉萨地块晚白垩世沉积岩—火山岩古地磁结果及其古地理意义

发布时间：2018-05-04 23:23

本文选题：碰撞时限 + 构造缩短量　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：印度板块与欧亚板块碰撞是新生代以来地质历史上重要地质事件之一。碰撞导致了喜马拉雅造山带和青藏高原的形成,碰撞及其之后的高原隆升强烈影响了青藏高原及其周边块体的构造演化;同时,碰撞还改变了青藏高原及周边水系分布与流向,对亚洲甚至全球气候都产生了巨大的影响。对印度与欧亚板块碰撞过程研究的主要问题之一在于精确限定其碰撞的初始时间和产生的构造缩短量。地学界广泛接受的印度与欧亚板块初始碰撞时间为~55Ma,碰撞后产生的构造缩短量为~1000km;但是对这一问题也存在很大的争议。印度与欧亚板块碰撞为近南北向的陆陆碰撞,那么碰撞最直接的证据就是缝合带两侧块体的古纬度的重叠。实践和研究证明古地磁学能定量地约束板块的边界及其演化历史,精确限定板块的古纬度,是制约板块碰撞时限、碰撞地点和碰撞模式的最理想方法之一。本论文选择拉萨地块林周盆地晚白垩世红层-火山岩序列,开展同位素年代学和构造古地磁学研究,从构造古地磁学的角度探讨印度与欧亚板块碰撞的时间和产生的构造缩短量,主要得出以下结论:(1)古地磁采样地层(上白垩统设兴组地层)的时代为69.75Ma-73.75Ma。(2)通过对比林周盆地晚白垩世沉积岩和火山岩古地磁结果,认为研究区区沉积岩记录的古地磁场磁倾角并不存在显著的磁倾角偏低现象。采样剖面获得的晚白垩世古地磁结果具有正极性和反极性两种极性,其特征剩磁方向为:Dg=13.2°,Ig=31.6°,k=36.4,α95=5.3°,地层校正后Ds=0.5°,Is=20.2°,k=25.5,α95=6.4°;对应的古地磁极位置为:70.5°N,269.6°E,A95=4.9°,古纬度为plat=10.4°N。(3)通过对比已有的古地磁数据,我们认为拉萨地块在晚白垩至古近纪一直处于北纬11°N-15°N左右的低纬度位置,并未发生明显的纬向运动。据此推算印度与欧亚板块初始碰撞时间为47Ma-54Ma。(4)通过对比本次研究得出的拉萨地块的古纬度实测值与拉萨地块和喜马拉雅地块古纬度期望值,认为约70Ma以来,拉萨块体与稳定欧亚大陆之间发生了1300±450km的构造缩短。
[Abstract]:The collision between the Indian plate and the Eurasian plate is one of the important geological events in the Cenozoic geological history. The collision resulted in the formation of the Himalayan orogenic belt and the Qinghai-Tibet Plateau, and the collision and the subsequent uplift of the plateau strongly affected the tectonic evolution of the Qinghai-Tibet Plateau and its surrounding blocks, and at the same time, the collision also changed the distribution and flow direction of the Qinghai-Tibet Plateau and its surrounding water system. It has had a huge impact on Asia and even on the global climate. One of the main problems in the study of the collision process between India and Eurasia is to precisely define the initial time and tectonic shortening of the collision. It is widely accepted in geoscience that the initial collision time between India and Eurasia plate is 55 Ma, and the tectonic shortening caused by collision is 1000 km, but this problem is also controversial. The collision between India and Eurasia is a continental collision near the north and south. The most direct evidence of the collision is the overlap of paleolatitudes of the blocks on both sides of the suture belt. It is proved by practice and research that paleomagnetism can quantitatively constrain the boundary of plate and its evolution history, and precisely define the paleolatitude of plate. It is one of the most ideal methods to restrict the time limit of plate collision, collision location and collision model. In this paper, isotopic chronology and tectonic paleomagnetism are carried out in the late Cretaceous red beds and volcanic rock sequences in Linzhou Basin, Lhasa block. From the perspective of tectonic paleomagnetism, the time and tectonic shortening of the collision between India and Eurasia plate are discussed. The main conclusions are as follows: (1) paleomagnetic sampling stratigraphy (upper Cretaceous formation) is 69.75 Ma-73.75 Ma.-2) by contrasting paleomagnetic results of late Cretaceous sedimentary rocks and volcanic rocks in Linzhou Basin. It is considered that the paleomagnetic field magnetic dip angle recorded in sedimentary rocks of the study area does not have a significant phenomenon of low magnetic dip angle. The paleomagnetic results of the late Cretaceous obtained from the sampling section have two polarities, namely, positive polarity and antipolarity. The remanent magnetic direction of the paleomagnetic field is: 1 DG 13.2 掳IgA 36.4 掳, 伪 955.3 掳, Ds=0.5 掳Isa 20.2 掳KG 25.5, 伪 956.4 掳; the corresponding paleomagnetic pole position is: 70.5 掳Nu 269.6 掳EKA 954.9 掳, and paleolatitude is plat=10.4 掳N. 3. The paleomagnetic data are compared by comparing the available paleomagnetic data. We think that the Lhasa block has been in the low latitude of 11 掳N-15 掳N from late Cretaceous to Paleogene, and there is no obvious zonal movement. The initial collision time between India and Eurasia plate is estimated to be 47 Ma-54 Ma. 4) by comparing the paleolatitude of Lhasa block with the expected value of paleo latitude of Lhasa block and Himalayan block, it is considered that since 70Ma, The tectonic shortening of 1300 卤450km occurred between Lhasa block and stable Eurasia.
【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】：P318.4;P531

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