Title: The Kinematics and Dynamics of Rifting in South-Central Tibet
Abstract: Southern Tibet is a unique location to study the complex interactions between continental collision and extension of the Earth’s upper crust, which forms linear structures called rifts. The study of rifts is important because the rocks they expose can record thermal changes in the Earth’s crust related to large-scale processes such as shifts in tectonic plates which occur over long timescales and are otherwise difficult to observe. Despite their importance, the kinematics and dynamics of rifting, or the processes that occur during rift formation and evolution, are not well understood. In this study, we use field and radiometric dating techniques to investigate the shape, orientation, and timing of extension in southern Tibet by testing kinematic models for two classes of rifts: (1) Tibetan rifts which are defined as rifts >150 km in length that crosscut the Lhasa Terrane, and (2) Gangdese rifts that are defined as rifts <50 km long that are isolated within the high topography of the Gangdese Range. Evaluation of extension timing across the Tangra Yumco (TYC) rift and three Gangdese rifts suggests TYC formed through the linkage of smaller normal fault segments into larger and longer structures over time, while Gangdese rifts may have formed and evolved with relatively constant lengths. Interactions between rifts and contractional structures have likely influenced the evolution of topography and drainage patterns in southern Tibet for at least the past sixteen million years. To further investigate these structural interactions, a broad compilation of thermochronology data compares results from this study to data from another Tibetan rift, the Lunggar rift. Results show all samples from Gangdese rifts and samples from Tibetan rifts which overlap the Gangdese Range produce estimates for rift timing between ~28-16 Ma, suggesting a more complex exhumation history than was previously recognized. Samples north of the Gangdese Range which better reflect rift timing produce ages between ~8-4 Ma. We interpret Gangdese rifts initiated in conjunction with, and perhaps balancing, uplift driven by the India-Asia collision, while young ages North of the Gangdese range (~8-4 Ma) reflect extension timing along Tibetan rifts.
Zoom Link: https://gatech.zoom.us/j/95963290955
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