Magmatic System of the Hainan Plume Revealed by Ambient Noise Tomography

Abstract

The magmatic system of the Hainan plume is important for unraveling the mechanism of intraplate volcanism. We develop a detailed three-dimensional shear-wave velocity (Vs) model of the crust and uppermost mantle using ambient noise tomography to investigate the magmatic system of the Hainan plume. Rayleigh wave phase velocity dispersions (5–40 s) are extracted from seismograms recorded at 74 broadband stations, including 32 Chinese provincial network stations and 42 portable stations of the Hainan Active Volcano Experiment of Seismic Array (HAVESArray). The integration of the HAVESArray data substantially improves the spatial resolution of the new Vs model. Our results show that high-Vs zones mainly exist under southern Hainan Island and northern Leizhou peninsula, whereas low-Vs zones appear primarily beneath the Beibuwan basin and the Leiqiong volcanic field. Two distinct low-Vs zones are revealed beneath the Leiqiong volcanic field. The deeper zone exists at depths of 24–40 km and has a Vs reduction of ∼5%, whereas the shallower zone exists at depths of 12–20 km and has a Vs reduction of ∼8%. The two low-Vs zones are connected vertically. These results suggest that the interconnected deep and shallow magma reservoirs may regulate the magma supply between the volcanic field and the Hainan mantle plume. Furthermore, seismic swarms in the Qiongshan area are predominantly located along the boundaries between high-Vs and low-Vs anomalies. We infer that the 1605 M7.5 Qiongshan earthquake was likely caused by the disruption of the overlying brittle crustal seal due to the rapid intrusion of the underlying magmatic fluids.