Mesozoic Tectonic Evolution in the Kurgovat-Vanch Complex, NW Pamir

Abstract

Different crustal deformation histories between Tibet and the Pamir reflect along-strike variations in geodynamics of the Tethys orogen. To investigate the less well-documented deformation history of the Pamir, which has been a barrier in understanding the nature of these differences, we conducted an integrated study in the Kurgovat-Vanch region, NW Pamir. The lithologies are primarily Ediacaran-to-Carboniferous metasedimentary rocks intruded by Carboniferous plutons, which then experienced Late Triassic to Early Jurassic regional metamorphism. Structural mapping and analyses document a low-angle NW-directed thrust fault, the Poshkharv thrust, separating the overlying upper-greenschist facies Poshkharv complex from the underlying amphibolite facies Kurgovat complex. Regional geologic maps indicate the Poshkharv thrust continues for ∼300 km across the NW Pamir. Our study also documents another regional thrust fault, the top-to-the-SE Vanch thrust that juxtaposes the Southern Kurgovat complex above the lower-grade Vanch complex in the south. Biotite 40Ar/39Ar thermochronology indicates Early Cretaceous movement on all structures with ∼135–125 Ma exhumation along the NW-directed Poshkharv thrust and ∼125–115 Ma exhumation along the SE-directed Vanch thrust. Regional crustal deformation in the Northern Pamir was formed in a Cretaceous retro-arc setting, unrelated to the Cenozoic India-Asia collision. Cretaceous deformation in the NW Pamir was broadly coeval with the NE Pamir, but preceded Cretaceous shortening and coeval arc magmatism in the Southern Pamir. We interpret Early Cretaceous thrusting and crustal thickening followed by southward migration of shortening and magmatic flare-up in the Pamir to have resulted from a transition of Neotethys subduction from northward flat-slab advancing to southward retreating. © 2022. American Geophysical Union. All Rights Reserved.