Collaborative Research: Investigation of Syncollisional Extension and Basin Development in the High Himalaya

来自亚利桑那大学和休斯顿大学的一个科学家小组正在研究喜马拉雅山脉隆起的扎达盆地地区从收缩到伸展的过渡性质。扎达盆地是喜马拉雅地区最大的晚第三纪盆地，其形成时代大致为晚中新世至更新世。由于萨特莱杰河（一条主要的向南流动的跨喜马拉雅流域）的切割，盆地填充物及其底层基底非常暴露。该盆地目前位于海拔约3500米的喜马拉雅冲断带腹地，并在一个区域广泛的早中新世至中中新世冲断系统的顶部开发。逆冲系统侧面的第二个主要盆地，凯拉斯盆地，这被认为是在第三纪中期的时间，但仍然不好过时。扎达盆地和凯拉斯盆地共同记录了该地区从高海拔到相对低海拔的崩塌，以及在短短几百万年内从侵蚀剥蚀到厚沉积物堆积的过渡。利用构造分析、热压法、氩-氩热年代学、盆地分析和氧同位素古高度测量等多学科方法，对：（1）曲苏姆拆离体、藏南拆离体和大逆冲断层的几何学、运动学和滑动规模，（2）凯拉斯逆冲盆地和扎达盆地的物源和沉降历史，（3）扎达盆地的古高程历史，（4）拉张拉张拉（4）主要断裂带出露的岩石记录的压力-温度-时间轨迹;（5）主要构造活动的深度。研究结果被用来确定：（1）喜马拉雅山这一地区高海拔伸展开始的时间，（2）扎达盆地及其周围伸展的运动学调节方式，（3）弧垂直和弧平行伸展的速率，（4）拉张作用的强度，（5）拉张作用的强度，（6）拉张作用的强度，（7）拉张作用的强度。（4）拉张作用开始时的高程，以及扎达盆地古高程和古沉积环境对拉张作用的响应;（5）扎达盆地古水系格局与现代Sutlej河源头整合的时间。通过对这些问题的回答，可以检验解释主要造山带从弧正常收缩到弧平行伸展转变的三种理论：（1）伸展发生在地壳过厚的区域;（2）伸展是由于弧形冲断前缘向外扩张;（3）伸展是由于中地壳的挤压。该项目涉及本科生和研究生的研究，与中国科学家的合作，以及在美国和中国的教育和推广工作。

A team of scientists from the University of Arizona and the University of Houston are investigating the nature of the transition from contraction to extension in the Zada basin area of the Himalayan uplift. The Zada basin is the largest late Tertiary basin in the Himalaya and is broadly constrained to be Late Miocene to Pleistocene in age. The basin fill and its underlying basement are spectacularly exposed owing to incision by the Sutlej River, a major southward-flowing trans-Himalayan drainage. The basin currently lies at approximately 3500 m elevation in the hinterland of the Himalayan thrust belt and developed on top of a regionally extensive Early to Middle Miocene thrust system. The thrust system flanks a second major basin, the Kailas basin, which is considered to have developed during mid-Tertiary time, but remains poorly dated. Together, the Zada and Kailas basins archive the collapse of this region from high to relatively low elevation and the transition from erosional denudation to thick sediment accumulation in only a few million years. The multidisciplinary study is using structural analysis, thermobarometry, argon-argon thermochronology, basin analysis, and oxygen isotope paleoaltimetry to place constraints on: (1) geometry, kinematics, and magnitude of slip of the Qusum detachment, South Tibetan Detachment, and Great Counter thrusts; (2) provenance and subsidence history of the Kailas thrust basin and Zada basin; (3) paleoelevation history of the Zada basin; (4) pressure-temperature-time paths recorded in the rocks exhumed by the major faults; and (5) the depth to which the major structures operated. Results are being used to determine the: (1) timing of onset of high-elevation extension in this part of the Himalaya; (2) mode of kinematic accommodation of extension in and around the Zada basin; (3) rates of arc-perpendicular and arc-parallel extension; (4) elevation at which extension began, and the evolution of paleoelevation and paleoenviornments of deposition in the Zada basin in response to ongoing extension; and (5) date at which the paleodrainage pattern in Zada basin become integrated into the headwaters of the modern Sutlej River. By answering these questions, three theories to explain the transition from arc-normal contraction and to arc-parallel extension in major orogenic belts are being tested: (1) extension occurs in regions of overthickened crust; (2) extension is due to outward expansion of the arc-shaped thrust front; or (3) extension is caused by extrusion of the middle crust. The project involves undergraduate and graduate students in the research, collaboration with Chinese scientists, and education and outreach efforts in both the United States and China.