Normal faulting, basin development, and paleoelevation in south Tibet and the evolution of the Tibetan Plateau

藏喜马拉雅造山带是早新生代以来印度板块与欧亚板块不断汇聚的结果。在这一漫长历史的后期（即中新世中晚期以来），几个南北向裂谷系统的形成解剖了青藏高原，突出了造山带演化的重大变化。西藏裂谷与高原隆升的关系是更好地认识整个造山带地质演化的关键。中德联合合作将聚焦于这一重大科学问题，研究吉隆裂谷和尼玛-定日裂谷的构造、沉积学和古海拔史。吉隆裂谷和尼玛-定日裂谷穿过拉萨地表，进入喜马拉雅山脉，绵延300多公里。德国小组（本建议）将应用低温热年代学（即裂变径迹和(U-Th)/He定年）对花岗岩侵入体沿高程剖面的磷灰石和锆石进行研究，这些侵入体暴露在裂陷断层下盘。各自数据的热运动学建模将使我们能够量化吉荣地堑和尼玛-定日裂谷系统沿走向的断层滑动的开始和时间变化。我们的中方合作伙伴将利用沉积学和磁地层学分析重建断裂控制的吉荣盆地的演化和沉积环境。在此基础上，他们将利用古土壤、自生矿物和化石中碳酸盐的稳定同位素分析来解读吉荣盆地的古海拔如何随时间变化及其与盆地边界断裂活动的关系。我们两个工作组的互补方法和结果将有助于更好地理解青藏高原裂谷发育、盆地形成和古海拔之间的因果关系，以及它们与过去气候变化的时间关系。

The Tibetan-Himalayan orogen is the result of the ongoing plate convergence between India and Eurasia since the Early Cenozoic. At a late stage of this long-lasting history (i.e. since the mid- to late Miocene), the formation of several N-S trending rift systems dissecting the Tibetan Plateau highlights significant changes in the evolution of the orogen. The relation between the rifts in Tibet and the uplift of the plateau is the key to a better understanding of the geological evolution of the entire orogen. The joint Sino-German cooperation proposed here will focus on this major scientific problem by investigating the tectonic, sedimentological, and paleoelevation history of the Gyirong and Nima-Dingri Rifts, which extend over a distance of more than 300 km through the Lhasa terrane and into the Himalaya. The German group (this proposal) will apply low-temperature thermochronology (i.e. fission track and (U-Th)/He dating) on apatite and zircon along elevation profiles through granitic intrusions, which are exposed in the footwalls of the rift-bounding faults. Thermokinematic modelling of the respective data will allow us to quantify the onset of normal faulting and temporal variations in fault slip along strike of the Gyirong graben and the Nima-Dingri rift system. Our Chinese partners will use sedimentological and magnetostratigraphic analyses to reconstruct the evolution and the depositional environment of the fault-controlled Gyirong basin. On this basis, they will use stable isotope analysis of carbonate from paleosols, authigenic minerals, and fossils to decipher how the paleoelevation of the Gyirong basin has changed through time and how it is related to the activity of the basin-bounding faults. The complementary approaches and results of our two working groups will lead to an improved understanding of the causal relation between rift development, basin formation, and paleoelevation on the Tibetan Plateau and their timing with respect to past climate changes.