Mantle diapir and inward intracontinental subduction: A discussion on the mechanism of uplift of the Qinghai-Tibet Plateau

In this chapter, we account for the mechanism of uplift of the Qinghai-Tibet Plateau beyond the subduction model of the Himalayas, through studies of features of Cenozoic deformation and the accompanying geological events, with a combination of results from geophysical exploration and experiments at the interior and hinterland of the plateau. Extensive alkaline volcanic rocks of Cenozoic age in the interior of the plateau are shoshonitic and high-K, formed by the partial melting of the lower crust and upper mantle in an extensional tectonic setting. A seismic converted-waves study from Golmud to Wenquan further shows that the lithosphere at the northern interior of the plateau has a multisandwich structure and lithospheric faults with sinistral strike-slip sense. The large low-velocity anomaly at the depths from 210 to 360 km beneath the Hoh Xil region, detected by seismic tomographic data, is interpreted to be a mantle diapir responsible for the genesis of the alkaline volcanic activity. A seismic reflection profile across the northern hinterland of the plateau shows that the North China craton was subducted southward beneath the Qilian Mountains. In the eastern hinterland, a wedge of the Yangtze craton embedded into the lower crust at the Longmenshan indicates that intracontinental subduction existed between the eastern Qinghai- Tibet Plateau and the Yangtze craton. The noncoaxial compression and oblique crustal shortening in the Qinghai-Tibet Plateau caused by northwest-southeast-trending compression at the northern margin and the south-north-trending compression at the southern margin are most likely responsible for the formation of strike-slip faults and rotation of blocks. We suggest a new model for the uplift of the Qinghai-Tibet Plateau: A mantle diapir in the interior and inward intracontinental subduction at the margin.