西藏荣玛乡冈塘错花岗岩就位机制及隆升剥露研究

发布时间：2018-06-17 22:09

本文选题：荣玛乡 + 冈塘错花岗岩　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：冈塘错中粗粒花岗岩形成于古特提斯洋俯冲消亡后的后碰撞伸展环境。前人对其地球化学特征、年代学特征有较为详细的研究,但是岩浆原生构造及后期隆升剥露信息研究薄弱。岩浆原生构造研究可以判断岩浆侵位时的流动方位,对探讨岩浆就位机制具有重要意义。冈塘错花岗岩在形成后经历了羌塘地区构造演化的多期事件,磷灰石裂变径迹研究能够揭示羌塘盆地或者青藏高原的隆升特征,对分析青藏高原演化具有重要意义。通过对岩体中流面、流线以及围岩劈理、线理特征进行统计分析,笔者认为冈塘错花岗岩在侵位过程中是顺E-W向构造带由北向南就位。通过对冈塘错花岗岩进行磷灰石裂变径迹(AFT)研究发现所有磷灰石单颗粒年龄处在145Ma-55Ma之间,主体为110Ma-55Ma。利用P(χ2)值和软件Binomfit分解获得4组有效池年龄和峰值年龄:125.9Ma,101.5Ma-91.1Ma,81.8Ma-70.8Ma和66.6Ma。其时代跨度为125.9Ma-66.6Ma,处于早白垩世晚期-晚白垩世,该年龄是对班公湖-怒江洋向北俯冲以及拉萨地体与羌塘地体碰撞拼合效应下构造热事件和抬升冷却事件的记录。利用磷灰石裂变径迹热史模拟发现所有样品经历的都是持续的单调冷却过程,每个样品均显示多次快速隆升冷却。主体上快速隆升冷却可分为两期,第一期为早白垩世晚期-晚白垩世(120Ma-77Ma),第二期为始新世末-至今(34Ma-至今)。第一期中120Ma-94Ma占主导;第二期又可细分为34Ma-19Ma和19Ma-至今,后者占主导。两期快速隆升期内隆升(剥蚀)量为2680m-3680m和1400m-2440m。第一期快速隆升是班公湖-怒江洋向北俯冲以及拉萨地体与羌塘地体碰撞造山的反映,该期隆升塑造了原青藏高原。第二期快速隆升是印度板块与欧亚大陆俯冲碰撞的远程效应,并在19Ma-至今远程效应在羌塘中部地区达到最大。
[Abstract]:The granitic granites were formed in the post-collision extensional environment after the subduction of the PaleoTethys Ocean. The geochemical and geochronological characteristics of the magma were studied in detail, but the information of magmatic primary structure and late uplift and exfoliation was not studied in detail. The study of magmatic primary structure can determine the flowing direction of magma emplacement, and it is of great significance to study the mechanism of magmatic emplacement. The Gangtang fault granite has experienced many events of tectonic evolution in Qiangtang area after its formation. The study of apatite fission track can reveal the uplift characteristics of Qiangtang basin or Qinghai-Tibet Plateau, and it is of great significance to analyze the evolution of Qinghai-Tibet Plateau. Based on the statistical analysis of the cleavage and linear characteristics of the flow plane, streamline and surrounding rock in the rock mass, the authors consider that the Gangtang fault granite is in position from north to south in the course of emplacement. Through the study of apatite fission track (AFT) of Gangtang dislocation granite, it is found that all apatite single grain ages are between 145 Ma and 55 Ma, and the main body is 110 Ma-55 Ma. The effective pool age and peak age: 125.9 Ma-101.5 Ma-91.1 Ma-81.8 Ma-70.8 Ma and 66.6 Ma were obtained by using P蠂 ~ 2 and Binomfit decomposition. The age span is 125.9 Ma-66.6 Ma, which is in late early Cretaceous to late Cretaceous. This age is the record of tectonic heat events and uplift cooling events due to northward subduction of Bangong Lake and Nujiang Ocean and collision of Lhasa terrane and Qiangtang terrane. Using the thermal simulation of apatite fission track, it is found that all samples undergo a continuous monotone cooling process, and each sample shows several rapid uplift cooling. The rapid uplift and cooling in the main body can be divided into two stages, the first stage is from the late early Cretaceous to the late Cretaceous, and the second is from the end of the Eocene to the present day, from the end of the Eocene to the present. In the first phase, 120 Ma-94 Ma dominated, and the second stage was subdivided into 34 Ma-19 Ma and 19 Ma-present, the latter dominating. The amount of uplift (denudation) in two periods of rapid uplift is 2680m-3680m and 1400m-2440m. The first stage of rapid uplift is reflected by the northward subduction of Bangong Lake-Nujiang River and the collision orogeny between Lhasa terrane and Qiangtang terrane which shaped the original Qinghai-Tibet Plateau. The second rapid uplift is the long-range effect of the collision between the Indian plate and the Eurasian continent, and the remote effect reached its maximum in the central Qiangtang area in 19Ma-present.
【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】：2017
【分类号】：P588.121;P542

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