Seismic Tomography Beneath the Dabie‐Sulu Col‐Lision Orogeny‐3‐D Velocity Structures of Litho‐sphere

Abstract

Abstract The 3‐D structure of seismic velocity of the crust and upper mantle beneath the region of 112°–124° E, 28°–39°N including the Dabie‐Sulu orogenic belt are reconstructed by using seismic tomography. The results demonstrate that both significant lateral heterogeneity of velocity structures exists in the crust and upper mantle beneath the Dabie orogenic belt, and a low velocity layer in the middle crust which corresponds to extensional and nappe structures. Beneath the southern and northern Dabie tectonic units, the Moho depresses and a north‐dipping high‐velocity (in range from 6.5 to 6.6 km/s) block, which corresponds to the ultrahigh‐pressure (UHP) metamorphic rocks, were developed in the crust. In the uppermost mantle beneath the orogenic belt was developed the north‐dipping high‐velocity slab. Combining with the geological and geochemistrical data, we inferred that the high‐velocity slab might be the remnants of ancient subducted Yangtze block. Seismic tomography reveals that the subducted ancient Yangtze block might be broken off. Our results indicate that the tomographic image have a significance on geodynamics of surface‐tectonic processes and in study of ancient orogenic belt.