Shortening of lower crust beneath the NE Tibetan plateau

Abstract We reprocessed a high-resolution deep seismic reflection profile to reveal the detailed crustal structure of the junction between the Qilian Shan-Nan Shan thrust belt and the Hexi Corridor basin in the NE Tibetan Plateau. The profile shows that the Moho discontinuity is characterized by complex dislocations and overlapping geometries. Restoration of the deformed Moho discontinuity reveals 50.2 km (35.5%) of Cenozoic lower-crustal shortening along the seismic profile. Compression of the lower crust produces crustal thickening of ∼12.8 km. This demonstrates that lower-crustal shortening plays a significant role in topographic uplift and crustal thickening at the NE margin of the Tibetan Plateau. Thus, we propose a double-layered shortening mechanism, with decoupled deformation of upper crust and lower crust. The proposed deformation mechanism differs from previous crustal shortening models for the northern, eastern, and northeastern Tibetan Plateau. Our model eliminates the need for lower-crustal flow to explain topographic uplift along the NE margin of the Tibetan Plateau.