South Tibetan Detachment System activity and leucogranite emplacement:Insights from the Shisha Pangma regions
The South Tibetan Detachment System(STDS)is the largest detachment fault zone in the world.As the key tectonic boundary fault,it also plays an important role in the Himalayan orogeny.Voluminous leucogranites intruded into the detachment and its footwall-the Great Himalaya Unit.Recent studies reveal high potential of rare-metal mineralization.Therefore,the tectonic history of the STDS and the emplacement of leucogranites are key to understanding the detachment deformation and evolution,and melts-fault interaction.To answer this question,this paper focuses on two regions near the Shisha Pangma,Gyirong and Nyalam,and discusses the evolution of the STDS and the mechanism of syn-tectonic migration-emplacement of leucogranites.Our work reveals a relatively thin detachment in Gyirong,which is tens to hundreds of meters thick,and has a narrow deformation zone.The top-to-the N normal-sense shearing has an insignificant effect on the Gyirong pluton and the Greater Himalaya Unit.In contrast,the detachment in Nyalam is kilometers-thick and mylonitized the Rouqiecun Group and the Great Himalaya Unit,causing highly deformed granitic sheets parallel to the detachment.We infer that the detachments of Gyirong and Nyalam represent different structural levels of the STDS,which can better explain the difference of deformation patterns.Their exhumation results from uneven tectonic denudation.By summarizing previous studies,we propose a new tectonic model in which the detachment migrates upwards assisted by the emplacement of leucogranites.During this tectonic-magmatic process,the early-formed,deep detachment controls the migration and emplacement of leucogranites.When the late leucogranites intrude and migrate to the high tectonic level,the main detachment plane also migrates upwards,leading to multiple detachment fault planes in the STDS.
South Tibetan Detachment SystemLeucograniteHimalayaDeformationEmplacementFault migration
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