Upper mantle velocity and its dynamic significance in the middle-southern segment of the Tan-Lu fault zone

Abstract

389 teleseismic events recorded by 126 seismic stations were used to study the upper mantle velocity structure of the central-southern segment of the Tan-Lu fault zone (TLF). Results show that (1) the upper mantle velocity presents strong lateral heterogeneity. The TLF is a velocity gradient zone with a depth of 40–120 km, and with a high-velocity anomaly on its west and a low-velocity anomaly on its east. However, at a depth of 300–400 km, the velocity anomalies on both side of the TLF have changed, with a low-velocity anomaly on its west and a high-velocity anomaly on its east. At a depth of 500–600 km, high velocity anomalies are observed on both sides of the TLF, (2) the high velocity anomalies H1 and H2 are located beneath the Dabie fault-fold belt and Lower Yangtze fault block, respectively. The H1 may be the delaminated lithosphere, while the H2 may represent the subduction of the Paleo- Pacific plate. The upper mantle velocity anomalies on both sides of the TLF may reveal the subduction of the Paleo-Pacific plate and the backarc retreat movements.