Crustal Deformations in the Northeastern Tibetan Plateau Revealed by Multiple Geodetic Datasets

The northeastern Tibetan Plateau (TP) is one of the best places to investigate the growth mechanism of the Tibetan Plateau due to its dramatic deformation. We calculate regional gravity changes and 3-D crustal deformations based on geodetic datasets, such as campaign gravity, GPS, and leveling observations. Obvious negative-positive gravity changing signals appear in both sides of the Qilian-Haiyuan fault, which indicate material accumulation and reduction, respectively. We therefore suggest that the northeastern TP thrust towards the North China Craton (NCC) is due to the northward advance of Tibetan Plateau. The crustal movement velocity decreases stepwise from south to north, which is bounded by the thrust or strike-slip faults, and varies from 15.4 +/- 0.1 mm/year in the Songpan-Ganzi block to 4.7 +/- 0.02 mm/year in the Alax block. The tectonic uplift rate from leveling observations, with surface loads and glacier isostatic adjustment (GIA) deformation corrected, show the fastest uplift zone occurring in the south Liupan Shan fault and West Qinling fault, with a rate of approximately 4.3 +/- 0.1 mm/year. In addition, we compare the material movement rate between the upper crust and mid-lower crust, and the results reveal that material movement in the mid-lower crust is faster than that in the upper crust, which may suggest the existence of a mid-lower crustal flow beneath the West Qinling block. We propose a geodynamic and kinematic model to quantitatively interpret the crustal deformations in the northeastern TP, which is helpful for further understanding the growth mechanism of the northeastern TP.