Deep crustal structure beneath the junction of the Qilian Shan and Jiuxi Basin in the northeastern margin of the Tibetan Plateau and its tectonic implications

The mechanism of crustal thickening in the Tibetan Plateau has long been a highly debated issue. The Tibetan Plateau continues to expanse outward at present, so the border areas as the leading edges of the plateau represent the latest deformation of the plateau, and are the critical places to study on crustal deformation and thickening of the plateau. Based on a deep seismic reflection profile across the junction of the Qilian Shan and the Jiuxi Basin in the northeastern margin of the Tibetan Plateau, combined with previous geological and geophysical data, this work obtained a clearly crustal deformation style beneath the junction of the Qilian Shan and the Jiuxi Basin by detailed geological interpretation of the seismic profile. The crustal deformation is bounded by a decollement layer at a depth of 14 24 km which is consistent with the upper boundary of the low velocity layer within crust. Crustal deformation above the decollement layer is featured by south-dipping, north thrusting faults which downwards ended at the decollement layer, implying the northward out-growth of the plateau. While the crust below the decollement layer experienced complicated shortening marked by a complex Moho geometry. We deduced that the decoupled upper crust and lower crust shortening played a critical role in the formation of the northeastern Tibetan Plateau, even in the formation of entire plateau.