The crustal and uppermost mantle structure of the Qinling-Tongbai-Dabie orogenic belt from integrated geophysical observations

The Qinling-Tongbai-Dabie orogenic belt (QD)is the important element of the China Central Orogenic Systems, which was formed by the convergence of the North China Craton and the Yangtze Craton. Due to its key position in the Central Orogenic Systems, the QD is an ideal place to study the orogenic processes between collided continents. To reveal the fine crustal and uppermost mantle structure with high resolution beneath the QD and surrounding areas, this work integrates seismic data available around the QD, which consist of raw seismic data, ambient noise data, and receiver function data. We adopted the Kirchhoff migration method to obtain a preliminary image of the Moho, used the H-kappa analysis to calculate the crustal thickness and V-P/V-S, and utilized a joint inversion of ambient noise and receiver functions to construct a high resolution V-S velocity model beneath the QD. Finally,we obtained a profile crossing the QD from west to east with detailed structures in the crust and uppermost mantle. The results reveal that : (1) Moho depth gradually becomes shallower from west to east,from the deepest about 55 km in the west to the shallowest about 30 km in the east of the profile. (2) The high velocity anomaly in the middle and lower crust of the West Qinling blocks the eastward expansion of the low velocity anomaly in the crust of the Northeast Tibetan Plateau, which provides unambiguous evidence that the crustal ductile flow within the Northeast Tibetan Plateau does not continue to flow eastward through the West Qinling. (3) In the uppermost mantle,the West Qinling is underlain by high velocity down to at least 100 km depth, the Tongbai and East Dabie are underlain by high velocity down to 70 km depth,however,the high velocity is not shown beneath East Qinling or East Dabie.

Automated summary

By integrating seismic data and utilizing high resolution imaging techniques, detailed structures of the crust and uppermost mantle in the Qinling-Tongbai-Dabie orogenic belt were revealed. The study found that Moho depth gradually becomes shallower from west to east along the profile, and high velocity anomalies exist in both the crust and uppermost mantle.