Seismic structure beneath the Tengchong volcanic area (southwest China) from receiver function analysis

Abstract

Tengchong is a young volcanic area on the collision boundary between the Indian and Euro-Asian plates of the southeastern Tibetan margin. Holocene volcanoes are concentrated in the Tengchong basin, where they align an N-S trending string-like cluster. To study the magma activity and its relation with the volcanoes, we deployed a passive seismic observation across the volcanic area in northern Tengchong. Using tele-seismic data and receiver function technique, we determined the S-wave velocity structure beneath nine temporary stations. Results show that the Tengchong basin is underlain by prominent low-velocity zones that are associated with the magma chambers of the volcanoes. In the north, a small and less pronounced magma chamber lies beneath two crater lakes, with a depth range of 9–16 km and a lateral width of <8 km. To the south, an interconnected magma chamber is found between the Dayingshan (DYS) volcano and the Dakongshan (DKS) volcanic cluster, with a depth range of 6–15 km and a lateral width of <12 km. In the south, the Laoguipo (LGP) volcano is characterized by anomalous low velocities throughout the upper-mid crust. Combined with other studies, we infer that the DYS volcano shares the same magma chamber with the DKS volcanic cluster, whereas the heat flow beneath the LGP volcano belongs to another thermal system, probably relating to the magma activity beneath the Rehai geothermal field in the south or affected by the intersection between the Tengchong volcanic fault zone and the Dayingjiang fault zone. In addition, mantle intrusion has resulted in the Moho elevation beneath the DKS volcanic cluster, and the thick transition zones on the crust-mantle boundary imply a possible penetration of the heat flow from the uppermost mantle into the lower crust.