Collaborative Research: Did the Altyn Tagh Fault Continue Beyond the Northern Margin of Tibet? Implications for Strain Accommodation During Continent-Continent Collision

印度与亚洲新生代碰撞的端元模型（连续地壳增厚与地壳块体挤出）对青藏高原及其周围构造的速率、运动学和空间范围做出了具体的预测。阿尔金断裂是一个活动的、长度超过1600公里的左旋构造，标志着青藏高原的北方边缘，在这些模型中起着关键而又不同的作用。连续体增厚模型预测ATF上的滑动速率缓慢，并要求ATF上的所有位移（约375公里），是由祁连山和柴达木盆地的地壳缩短。挤压模型预测ATF上的高滑移率，并要求其继续超出平台或将其滑移转移到其他结构。最近对沿ATF中东部沿着新生代沉积盆地的研究表明了两个运动阶段：第一，晚渐新世-早中新世断层中东部的大规模（约310公里）和高速率滑动;第二，中中新世-近代有限滑动（约65公里）和较低速率滑动。这些结果表明，阿尔金断裂在渐新世-早中新世发生了板状侧向挤压变形，中中新世变形方式转变为分布性缩短和增厚。然而，推断的渐新世-早中新世横向挤压的早期阶段，需要从ATF超出东北青藏高原的滑动转移，但已知的候选结构的研究未能确定任何适当的滑动幅度或时间。所检验的假说是渐新世-早中新世西藏沿着ATF向东的侧向挤压受到了西藏东北阿拉善地区的左旋断裂的调节，该断裂随后在中新世中期变得不活动。候选构造已在阿拉善地区填图，是切割白垩纪地层的左行断层。阿拉善地区的野外工作包括地质填图、这些主要断裂的运动学分析和盆地分析，以确定断裂系统的分布和构造几何学。将上述技术与物源分析、与新生代沉积矿床的横切和重叠关系的记录以及新生代岩石中下降异常的古地磁测定相结合，提供了这些构造的详细滑动历史和差异垂直轴旋转。这项研究的最终结果将促进对喜马拉雅-青藏山脉带如何演化以及印度和欧亚大陆之间的碰撞如何适应的理解。作为一个著名的自然实验室，该地区对于研究控制大陆变形的一阶过程以及山脉带如何随时间演变至关重要。这些大陆变形和山脉隆起的过程反过来也很重要，因为它们影响区域和全球气候、自然资源的分布，并影响广泛的其他地球系统过程。 除了这项研究的科学目标，该项目还支持路易斯安那州立大学、印第安纳州大学和加州大学、圣克鲁斯的研究生和本科生培训，并将为这些学生提供国际研究经验。这项研究还涉及美国研究人员与中国同行的合作。为印第安纳州大学合作的部分资金是由NSF的构造学教授和NSF的国际科学与工程办公室提供的。

End-member models of the Cenozoic collision of India with Asia (continuum crustal thickening vs. extrusion of crustal blocks) make specific predictions about the rates, kinematics, and spatial extent of structures in and around the Tibetan Plateau. The Altyn Tagh fault, an active greater than 1600 kilometer long left-lateral structure that marks the northern margin of the Tibetan Plateau, plays key, yet different roles in these models. Continuum thickening models predict slow rates of slip on the ATF and require that all displacement on the ATF (approximately 375 kilometers), is accommodated by crustal shortening in the Qilian Shan and Qaidam basin. Extrusion models predict high rates of slip on the ATF and require it to continue beyond the plateau or transfer its slip to other structures. Recent studies of Cenozoic sedimentary basins along the central-eastern ATF have demonstrated two phases of motion: first, Late Oligocene-Early Miocene large magnitude (approximately 310 kilometers) and high rates of slip on the central-eastern segment of the fault and second, limited mid-Miocene-Recent slip ( approximately 65 kilometers) and lower rates . These results suggest that the Altyn Tagh fault accommodated plate-like lateral extrusion in the Oligocene-Early Miocene, and that the mode of deformation changed to distributed shortening and thickening in the mid-Miocene. However, the inferred earlier phase of Oligocene-Early Miocene lateral extrusion requires that slip be transferred from the ATF beyond the NE Tibetan Plateau, but studies of known candidate structures have failed to identify any with the appropriate slip magnitude or timing. The hypothesis being tested is that Oligocene-Early Miocene eastward lateral extrusion of Tibet along the ATF was accommodated by left-lateral faults in the Alxa region, northeast of Tibet, which subsequently became inactive in the mid-Miocene. Candidate structures have been mapped in the Alxa region and are left-lateral faults that cut Cretaceous strata. Fieldwork in the Alxa region includes geological mapping, kinematic analysis of these major faults, and basin analysis to determining the distribution and structural geometry of the fault systems. Combining the techniques above with provenance analysis, documentation of cross-cutting and overlapping relationships with Cretaceous-Cenozoic sedimentary deposits, and paleomagnetic determinations of declination anomalies in Cretaceous-Cenozoic rocks provides detailed slip histories and differential vertical axis rotations for each of these structures. The final results of this research will advance understanding of how the Himalayan-Tibetan mountain belt evolved and how collision between India and Eurasia was accommodated. As a prominent natural laboratory, this region is critical for studying the first order processes that control how continents deform, and thus how mountain belts evolve through time. These processes of continental deformation and mountain uplift are in turn important, because they influence regional and global climate, distribution of natural resources, and influence a wide range of other Earth System processes. In addition to the scientific objectives of this research, the project is supporting graduate and undergraduate student training at Louisiana State University, the University of Indiana, and the University of California, Santa Cruz and will provide international research experiences for these students. The research also involves collaboration between U.S. researchers and their counterparts in China. Funding for the Indiana University part of the collaboration is provided by the NSF Tectonics Progran and the NSF Office of International Science and Engineering.