The crust structures and the connection of the Songpan block and West Qinling orogen revealed by the Hezuo-Tangke deep seismic reflection profiling

Abstract

The Songpan block in the northeastern Qinghai–Tibet Plateau (QTP) located at the junction of the E–W- and N–S-trending tectonic belts has affected the formation and evolution of the Chinese continent since Mesozoic and is a tectonic node in the central part of the Chinese continent. In this study, the Hezuo-Tangke deep seismic reflection profiling of the 257km-long was conducted in 2004, which is the first profile across the Songpan block and the West Qinling orogen. We reprocessed the data in 2009, and the results revealed the fine lithosphere structure of the northern margin of the Songpan block and the West Qinling orogen. The results also revealed the connection between the Songpan block and East Kunlun–West Qinling orogeny, indicating that the Songpan block and the West Qinling orogen belong to the same stable continental block and that their lower crusts are both characterized by north-dipping strong reflectors, which provide seismic evidence for subduction of the lower crust of the Songpan block beneath the West Qinling orogen. We found that the sub-horizontal Moho reflectors beneath the West Qinling orogen indicate that it underwent intensive extension after collisional orogeny. The results of this study also indicate that the Kunlun fault did not cut off the Moho. Actually, it terminated at a sub-horizontal decollement in the lowermost crust of Tibet at a depth of ~35km. The data provided through the investigation also are helpful in evaluating prospective oil and gas resources in the Songpan block.