Crustal structure of the Paleozoic Kunlun orogeny from an active-source seismic profile between Moba and Guide in East Tibet, China

We herein present a new seismic refraction/wide-angle reflection profile that crosses the Songpan-Ganzi terrane, the Animaqing suture zone and the eastern Kunlun mountains (comprised of the South Kunlun and Middle Kunlun blocks separated by the Middle Kunlun fault). The profile is 380 km long and extends from Moba to Guide in eastern Tibet. The crustal thickness is about 62 km under the Songpan-Ganzi terrane, 6264 km under the South Kunlun, and 60 km under the Middle Kunlun block. The Songpan-Ganzi flysch seems to be present up to a depth of 15 km south of the Animaqing suture zone, and up to a depth of 10 km in the Middle Kunlun block, with thicknesses elsewhere that depend on assumptions about the likely lithologies. The profile exhibits clear lateral variations both in the upper and lower crust, which are indicative of different crustal blocks juxtaposed by the Kunlun fault system. Whether or not the Songpan-Ganzi flysch was originally deposited on oceanic crust, at the longitude of our profile (100 degrees E) it is now underlain by continental crust, and the presence of continental crust beneath the Songpan-Ganzi terrane and of a continental arc under the South Kunlun block suggest Paleozoic continent-continent arc collision in the eastern Kunlun Mountains. Comparison of crustal velocity columns from all wide-angle seismic profiles across the eastern Kunlun mountains indicates a remarkable west-to-east change in the Moho topography across the Kunlun fault system (15-20 km Moho step at 95 degrees E, but only 2-5 km along our profile at 100 degrees E). Lower-crustal thickness of the Kunlun terranes is rather uniform, about 35 km, from 80 degrees-95 degrees E, which suggests that similar thrust-thickening processes have played a role where the Qaidam Basin abuts the Kunlun fault, but thins to 2025 km at 100 degrees E, east of the Qaidam Basin. The increased crustal thickness from 93 degrees to 98 degrees E compared to that at 100 degrees E may be due to the differences in the thickness of the crust of the two plates before their collision, and/or largely achieved by thickening of the lower crust, perhaps indicating a crustal flow mechanism operating more strongly in the western region. (C) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.