Collaborative Research: Integrated Tectonic and Paleomagnetic Study of the Early Cenozoic Rotation and Extrusion of Asian Crust Around the Eastern Himalayan Syntaxis

来自新墨西哥州大学和马萨诸塞州理工学院的一个研究小组正在研究大陆岩石圈变形形成构造结的过程，在东喜马拉雅构造结周围的活跃变形区域，造山带内的区域在短距离内结构组构的方向发生明显变化。滇西兰坪-思茅褶皱带上侏罗统-下第三系红层的研究表明，早新生代东南亚挤压过程是复杂的、不均一的。兰坪-思茅褶皱带西部部分地壳垂直轴的顺时针旋转高达120度，而东部则明显保持不旋转。据推断，这两个部分的带是分开的一个以前未被识别的剪切带，发挥了主要作用的挤压过程。这些结果表明，在东喜马拉雅构造结和其他构造结地区，挤压的流行范式，涉及翻译的离散块，保持内部未变形，是不一致的几个意见。类似的复杂性可能存在于其他部分，即兰坪-思茅带以西的挤压的印度支那地壳碎片。该项目将古地磁和构造研究扩展到印度支那地壳碎片挤出的其他地区，以更广泛详细地确定喜马拉雅东部结周围地壳碎片的变形，包括平移和旋转。主要重点是：（2）越南西北部，兰坪-思茅褶皱带最南端出露;（3）青藏高原东部的羌塘组，出露的白垩系/古近系岩石是兰坪-思茅带向北的延续;（4）楚雄盆地的部分地区，（5）兰坪-思茅带以西的城陵岭-孟梁、林昌单元，侏罗系红层出露较好。该项目将更好地确定东南亚经历大幅度地壳旋转的部分地区的区域范围，并将这些信息与观测相结合，以更好地了解整个自上而下的亚洲岩石圈在印度碰撞期间如何变形。该研究区，以及整个喜马拉雅地区的一部分，从伊比利亚半岛延伸到东南亚的尖端的广泛的碰撞带，一直是相当大的地质兴趣的主题几十年来和成因的大同轴区域仍然是一个一级的争议在构造。该项目将提供重要的洞察这些大型结构形成的过程。本科生和研究生在本研究的实验室和现场部分获得了宝贵的经验。重要的是，他们和他们的导师受益于与来自中华人民共和国和越南的科学家的密切合作。

A research team from the University of New Mexico and Massachusetts Institute of Technology is investigating the processes by which continental lithosphere is deformed to form syntaxes, regions within orogenic belts where there is a pronounced change in the orientation of structural fabrics over a short distance, in the actively deforming region around the Eastern Himalayan syntaxis. Previous work on the upper Jurassic to lower Tertiary redbeds in the Lanping Simao fold belt of western Yunnan indicates that the process of early Cenozoic extrusion of southeast Asia is complicated and heterogeneous. Specifically, clockwise vertical axis rotation of parts of the crust have been as large as 120 degrees in the western part of the Lanping Simao fold belt, whereas the eastern part remains apparently unrotated. It is inferred that the two parts of the belt are separated by a previously unrecognized shear zone that played a major role in the extrusion process. These results suggest that the prevailing paradigm for extrusion at the eastern Himalayan syntaxis and other syntaxial areas, involving translation of discrete blocks that remain internally undeformed, is inconsistent with several observations. Similar complexities probably exist for other parts, namely to the west of the Lanping-Simao belt, of the extruded Indochina crustal fragments. This project extends paleomagnetic and tectonic studies into other regions of the extruded Indochina crustal fragment to define in more extensive detail the deformation, including translation and rotation, of crustal fragments around the eastern Himalayan syntaxis. The primary focus is on: (1) the Baoshan tectonic element in far southwest Yunnan province, where lower Tertiary strata are exposed close to important structures; (2) northwest Vietnam, where the southernmost part of the Lanping Simao fold belt is exposed; (3) the Qiangtiang elements in eastern Tibet, where Cretaceous/ Paleogene rock, as the northward continuation of the Lanping-Simao belt are exposed (4) selected parts of the Chuxiong basin, northeast of the Red River Fault system; and (5) the Chengling-Mengliang and Linchang elements, immediately west of the Lanping-Simao belt, where Jurassic red beds are well-exposed. This project will better define the regional extent of parts of Southeast Asia that have experienced large magnitude crustal rotations and integrate this information with observations to better understand how the entire top down to bottom up Asian lithosphere has deformed during India's collision. The study area, as well as the entire Himalayan region as part of a broad collisional belt stretching from the Iberian Peninsula to the tip of Southeast Asia, has been the subject of considerable geological interest for decades and the genesis of the great syntaxial regions remains a first-order controversy in tectonics. This project will provide important insight into the processes by which these large structures form. Undergraduate and graduate students are gaining valuable experience in the laboratory and field components of this study. Importantly, they and their mentors benefit from close collaborations with scientists from People's Republic of China and Vietnam.