Subduction–collision and exhumation of eclogites in the Lhasa terrane, Tibet Plateau

Abstract

The Tibet Plateau is a key region to understand the evolution of the Tethys Oceans. The finding of Permian–Triassic eclogites and Carboniferous–Triassic ophiolites indicated the existence of a Paleo–Tethys Ocean in the Lhasa terrane, although the mechanism of subduction and exhumation mechanism of the high–pressure rocks remains equivocal. Here we focus on deformation, metamorphism, and geochronology of key rocks in the Sumdo area with a view to constrain the tectonic evolution of the Tethys Ocean and the geodynamic mechanism of eclogite exhumation. Structural analysis indicates two main stages of deformation (D1 and D2) in the study area. The D1 deformation (264–235 Ma) is dominated by penetrative Sn+1 foliation and solid rheological folds, resulted from the first type eclogites (~260 Ma), with exhumation at ~240 Ma along the subduction channel. The D2 deformation (213–180 Ma) is characterized by the tight and isoclinal overturned folds and thrust faults, related with the collisional exhumation (~200 Ma) of the second type eclogite (~230 Ma). Spreading of the Bangong–Nujiang and Indus–Yarlung Zangbo Tethys Oceans triggered the closure of Sumdo Tethys Ocean, as well as their initial subduction.