Two crustal flowing channels and volcanic magma migration underneath the SE margin of the Tibetan Plateau as revealed by surface wave tomography

Abstract

The SE margin of the Tibetan Plateau is an important area to develop a better understanding of the plateau uplift and the Indian-Eurasian continental collision dynamics. Previous studies have reported widespread low-velocity anomalies beneath this region, particularly in the Tengchong volcanic field (TCVF). However, the spatial distribution and dynamic processes of these low-velocity anomalies are not well constrained. In this study, a 3-D S-wave velocity structure model of the crust and upper mantle (10–120km) in the region is constructed by the inversion of surface wave dispersion data. A two-step inversion procedure is adopted to generate the S-wave velocity structure images. The measured phase velocities and inverted S-wave velocities jointly show a large-scale low-velocity anomaly distributed in the crust, consistent with the view that the region is the passageway of the eastward migration of Tibetan Plateau material. Two crustal flowing channels are clearly observed at depths of ∼20km and ∼30km, which connect and rotate clockwise around the Eastern Himalaya Syntaxis. Beneath the TCVF, there are two prominent low-velocity anomaly zones at depths of ∼15–25km and ∼50–80km, which indicate the existence of magma chambers. One of the crustal flowing channels is connected with the magma chamber of the TCVF, and the other has a short branch north of Kunming toward the Mile-Shizong fault at a depth of 20km. Based on the distribution of the S-wave velocities under the TCVF, a dynamic model of the Tengchong volcano magma system is proposed to explain the migration patterns of the volcanic material.