Sedimentary response to tectonic events: Reconstructed spatio-temporal scale of the Indo-Asian continental collision and Qinghai-Xizang Plateau uplift

The stratal geometries and lithofacies patterns in sedimentary basins are thought to be potentially important sedimentary indicators of tectonic events and record the uplift history of the areas around orogenic belts or along active basin margins. The first occurrence of new clast types in the depositional sequences has been used to mark initial uplift. The normal or reverse distribution of clasts throughout a vertical section corresponding to a specific source may be expressed as episodic tectonism.The ages of conglomerate intervals in foreland basins are generally believed to represent the time of thrust sheet activity. Alternative coarsening- or fining-upw ard cyclothems 100 m thick in extensional basins are usually interpreted to be rejuvenated tectonic uplift and retrograded headw ard erosion. Recent research shows that the onset of fine-grained fluvial and lacustrine deposition is more consistent with rapid subsidence in rift, pull-apart and foreland basins.The coarse-grained beds within the basins record postorogenic denudation and progradation of gravel wedges during intervals of tectonic quiescence. If tectonic loading due to crustal compression and thickening drives both the uplift of the mountain summits and asym metric subsidence, a wedge of sedimentary rocks thickens tow ard the mountain front and longitudinal river systems are dominant.When erosion unloading causes isostatic uplift of remaining peaks, a tabular depositional geometry of conglomerate strata in cross sections and transverse drainage patterns perpendicular to mountains are present. According to the theory of sedimentary response to tectonic events, we propose here that Cenozoic sedimentary basins on and around the Qinghai-Xizang Plateau may provide significant evidences of tectonic changes in different spatio-temporal scales. It may be an important approach to test and constrain present dispute in regard to initio Indo-Asian continental collision, synchronism and diachronism of the Qinghai-Xizang Plateau rising and grow th, as well as deform ation accommodation styles.