MESOZOIC TECTONIC EVOLUTION OF THE KURGOVAT COMPLEX, NW PAMIR

Recent studies have recognized that upper crustal shortening of the Pamir orogenic salient occurred primarily during Mesozoic. However, the extent, timing, and magnitude of Mesozoic crustal shortening in the Pamir are not well established. In this study, we applied field geological mapping and structural analysis, metamorphic P-T calculations, zircon U-Pb geochronology, and biotite Ar-Ar thermochronology on the Kurgovat complex in the NW Pamir to better understand its tectonic evolution. Our field mapping combining with microstructural analyses show that the Kurgovat complex was imbricated by a top-to-the NW thrust fault, the Poshkharv thrust, and the top-to-the S North Vanch thrust fault. These two thrust faults juxtaposed the Poshkharv Hanging-wall on the top of the Kurgovat-Lyaksh metamorphic terrane, and the Lyaksh terrane on the top of Vanch Hanging-wall terrane, respectively. Metamorphic P-T calculations yield peak metamorphic conditions of the Kurgovat-Lyaksh terranes, Poshkharv hanging-wall terrane, and Vanch Hanging-wall terrane of ~650 °C/7-9 kbar, ~560 °C/6 kbar, and ~400°C/~3-4 kbar, respectively. A large pluton which intrudes the Kurgovat terrane yields a zircon U-Pb age of ~330 Ma. Metamorphic zircon rims date greenschist to amphibolite facies metamorphism to 220-200 Ma. Biotite Ar-Ar dating yields cooling ages of 135-123 Ma from the samples surrounding the Poskharv thrust and 115 Ma from the samples surrounding the North Vanch thrust. Our research shows that the Kurgovat region of the northwest Pamir represents a Triassic Barrovian metamorphic terrane imbricated during the Cretaceous: Greenschist to amphibolite facies metamorphism occurred during final closure of the Paleotethys Ocean in the Triassic immediately prior to accretion of Gondwanan terranes along the southern Asian margin. During the Cretaceous, northward subduction of the Neotethys Ocean triggered imbrication of North Pamir Kurgovat complex with top-to-the NW thrusting from ~135-125 Ma, followed by top-to-the-S thrusting from ~125-115 Ma.