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

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语法结构的过程，造山带内的区域，在东喜马拉雅语法结构周围活跃变形的区域，短距离内结构织物的方向发生明显变化。前期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，东南亚早新生代挤压过程是复杂且非均质的。具体而言，兰坪思茅褶皱带西部部分地壳垂直轴顺时针旋转已达120°，而东部则明显未发生旋转。据推测，皮带的两个部分被一个以前未被识别的剪切区分开，该剪切区在挤出过程中发挥了主要作用。这些结果表明，喜马拉雅东部构造和其他构造区域的普遍挤压范式，涉及内部未变形的离散块的平移，与一些观察结果不一致。类似的复杂性可能存在于其他部分，即兰坪-思茅带以西的挤压印度支那地壳碎片中。该项目将古地磁和构造研究扩展到挤压的印度支那地壳碎片的其他区域，以更广泛地详细定义东喜马拉雅构造结周围地壳碎片的变形，包括平移和旋转。主要关注点是：（1）位于云南省西南部的保山构造单元，该构造单元下第三系地层出露，靠近重要构造； （2）越南西北部，兰坪思茅褶皱带最南端出露； （3）西藏东部的羌田元素，其中出露白垩系/古近系岩石，作为兰坪-思茅带的向北延续。（4）红河断裂系东北部楚雄盆地的部分地区； (5)兰坪-思茅带以西的城岭-孟良和临昌地层，侏罗系红层出露良好。该项目将更好地定义经历过大规模地壳旋转的东南亚部分地区的区域范围，并将这些信息与观测结果相结合，以更好地了解整个亚洲岩石圈在印度碰撞期间如何变形。该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界关注的焦点，而大构造区的起源仍然是构造学中的首要争议。该项目将为这些大型结构的形成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部分中获得了宝贵的经验。重要的是，他们和他们的导师受益于与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.