Crustal thickening and variations in architecture from the Qaidam basin to the Qang Tang (North-Central Tibetan Plateau) from wide-angle reflection seismology

Across the North Kun Lun-Qaidam block, variations of crustal thickness are detected, with Moho depth between 55 and 65 km, and an inverse correlation with basement topography. In the north of the Bayan Har block, a strong heterogeneity in the middle of the 70 km thick crust is shown. As suggested from synthetic seismograms modelling, it may result from thin layer inclusion marking the northward tectonic superposition of the Bayan Har crust on the North Kun Lun crust. As imaged by a fan profile, the corresponding upper part could have been transported northwards to thicken also the upper crust of the present North Kun Lun block. In the north of Qang Tang, a model is obtained with a 75-km thick crust and a lower half of the crust with average velocities characteristic of felsic composition. From Bayan Har to Qang Tang, variations of deep architecture are documented across the Jinsha suture and Xianshuihe fault from recording in-line and broadside to several shotpoints. Together with the felsic composition of the lower part of the crust, a Moho offset suggests the imbrication of the Bayan Har crust in the Qang Tang lithosphere between a south-dipping Moho above and a north-dipping Moho below. A model of indentation of the Qang Tang by an originally thinner Bayan Har crust and lithosphere, with part of the Qang Tang brought to greater depth would also be consistent also with the Moho topography across the transition from the Qang Tang to Bayan Har, as imaged by fan profile.