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

来自新墨西哥大学和麻省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的过程，在造山带内，在短距离内构造结构的方向发生明显变化的区域，在东喜马拉雅构造周围的活跃变形区域。前人对滇西兰坪-思茅褶皱带上侏罗统至下第三系红层的研究表明，早新生代东南亚挤压作用是复杂而非均质的。具体而言，在兰平-思茅褶皱带的西部，部分地壳的顺时针垂直轴旋转已达120度，而东部则明显处于不旋转状态。由此推断，带的两个部分被一个以前未被认识到的剪切带分开，该剪切带在挤压过程中起了主要作用。这些结果表明，在东喜马拉雅构造合带和其他构造合带区域的普遍挤压模式，包括内部未变形的离散块体的平移，与一些观测结果不一致。在挤压的印度支那地壳碎片的其他部分，即兰平-思茅带以西，可能也存在类似的复杂性。本项目将古地磁和构造研究扩展到挤压印度支那地壳碎片的其他区域，以更广泛地详细定义喜马拉雅东部合带周围地壳碎片的变形，包括平移和旋转。重点研究：(1)滇西南远缘宝山构造元，下第三系地层暴露于重要构造附近；(2)越南西北部，露出兰平-思茅褶皱带最南端；(3)藏东羌江元素，白垩系/古近系岩石为兰平-思茅带的北延部；(4)红河断裂系东北楚雄盆地部分地区；(5)兰平-思茅带以西的城岭-孟梁和临昌元素，侏罗纪红层发育良好。该项目将更好地确定东南亚部分地区经历了大震级地壳旋转的区域范围，并将这些信息与观测相结合，以更好地了解整个从上到下的亚洲岩石圈在印度碰撞期间如何变形。研究区域，以及整个喜马拉雅地区，作为从伊比利亚半岛延伸到东南亚尖端的广阔碰撞带的一部分，几十年来一直是地质学上相当感兴趣的主题，大合成区的成因仍然是构造学上的一级争议。这个项目将为这些大型结构形成的过程提供重要的见解。本科生和研究生在本研究的实验室和现场组件中获得宝贵的经验。重要的是，他们和他们的导师受益于中华人民共和国和越南科学家的密切合作。

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.