Crustal tilting and differential exhumation of Gangdese Batholith in southern Tibet revealed by bedrock pressures
Crustal tilting and differential exhumation of Gangdese Batholith in southern Tibet revealed by bedrock pressures
复制标题
DOI：
10.1016/j.epsl.2020.116347
复制
发表时间：
2020-08-01
影响因子：
5.3
通讯作者：
Burgess, Quentin R.
中科院分区：
文献类型：
--
作者：
Cao, Wenrong;Yang, Jiaming;Burgess, Quentin R.
藏南冈底斯玄武岩的折返历史，关系到岩浆作用和构造作用如何与一个长期存在的岩浆造山带的表面过程相互作用。在这项研究中，我们应用Alin-Hornoussa气压计测量冈底斯东部的岩体侵位压力。我们的研究结果，结合现有的基岩压力数据，揭示了整个冈底斯砾岩的区域古深度模式。岩基的西部靠近拉萨，暴露出侵位在1-2千巴的岩体，而东部靠近林芝，暴露出地壳记录压力通常为6- 1 - 2千巴。我们将压力数据与新发表的锆石U-Pb年龄相结合，以约束冈底斯榴辉岩的折返历史。结果表明，自100 Ma以来，上地壳经历了有限的折返，除了一个明显的渐新世-中新世脉冲。中下地壳经历了复杂的折返和埋藏历史，反映了大陆弧发育和陆-陆碰撞等重大构造事件。自CA。10 Ma以来，林芝东段经历了快速的折返（总折返长度> 40 km），这可能与东喜马拉雅构造结的折返有关。拉萨段的挖掘工作相对有限（挖掘总长度不到10公里）。这种戏剧性的差异剥露沿着东西方向要求冈底斯岩石倾斜到今天的曝光水平。我们的研究表明，在岩浆造山带的演化过程中，上地壳和中下地壳可以表现出不同的行为，折返历史反映了综合的构造，岩浆和地表过程。地表侵蚀速率的估算可以用来计算CO2的消耗，并评估岩浆造山带在长期碳循环中的作用。由于冈底斯玄武岩在一个相对连续的地壳剖面上有大量的深成岩和变质岩出露，因此它具有很大的潜力，可以作为了解大陆地壳结构和演化的天然实验室。(C)2020爱思唯尔B. V.保留所有权利。
The exhumation history of the Gangdese Batholith, southern Tibet, bears on how magmatism and tectonism interact with surface processes in a long-lived magmatic orogen. In this study, we applied Alin-hornblende barometry across the eastern Gangdese Batholith to obtain pluton emplacement pressures. Our results, together with existing bedrock pressure data, reveal the regional paleo-depth pattern across the Gangdese Batholith. The western part of the batholith, near Lhasa, exposes plutons emplaced at 1-2 kbar whereas the eastern part, near Nyingchi, exposes crust recording pressures typically of 6-12 kbar. We coupled pressure data with new and published U-Pb zircon ages to constrain the exhumation history of the Gangdese Batholith. The results show that since 100 Ma, the upper crust experienced limited exhumation except a pronounced Oligocene-Miocene pulse. In contrast, the middle-lower crust experienced a complex exhumation and burial history, reflecting major tectonic events including the development of continental arc and continent-continent collision. Since ca. 10 Ma, the eastern Nyingchi sector experienced fast exhumation (total exhumation > 40 km), which was likely related to the exhumation of the Eastern Himalayan Syntaxis. The Lhasa sector experienced comparatively limited exhumation (total exhumation < 10 km). Such dramatic differential exhumation along the E-W direction requires that the Gangdese Batholith was tilted to present-day exposure levels. Our study shows that during the evolution of a magmatic orogen, the upper and middle-lower crust can behave differently, and the exhumation history reflects integrated tectonic, magmatic, and surface processes. The surface erosion rate estimates can be used to calculate CO2 consumption and evaluate the roles of magmatic orogens in the long-term carbon cycle. Given its great exposures of plutonic and metamorphic rocks across a relatively continuous crustal section, the Gangdese Batholith has great potential to serve as a natural laboratory to understand the structures and evolution of the continental crust. (C) 2020 Elsevier B.V. All rights reserved.