The mechanism of phreatomagmatic maar-diatreme eruption in the Lei-Hu-Ling volcanic area of northern Hainan Island, China: Insights from magnetotelluric and magnetic data

Abstract

A maar-diatreme forms in response to the phreatomagmatic eruption caused by violent interaction between magma and externally derived water. Experimental work on phreatomagmatic eruptions has yielded considerable knowledge on maar-diatremes. However, the mechanism and process at natural scale remain poorly understood, especially when surface deposits are present. This paper presents a magnetotelluric and magnetic study of the Late-Pleistocene maar-diatreme volcanoes in the Lei-Hu-Ling area of northern Hainan Island, China. The regional 3D electrical structures show shallow high resistivities below craters and a low resistivity layer overlying the deep high-resistivity basement. The local magnetic structure of maar Luo-Jing-Pan reveals a cylinder-like diatreme with high susceptibility. The shallow low-resistivity zone, which coincides with the Fushan depression controlled by the Changliu-Xiangou Fault, is associated with the accumulation of high-salinity fluids with high porosity. The considerable volume of water stored in the Fushan depression and the sedimentary basement ridges beneath maars could have enabled a high level of magma-water interaction. This indicates a fault-controlled type for the phreatomagmatic eruption in the Lei-Hu-Ling volcanic area. The explosion depth is at least 600 m for Ru-Huang-Ling and Luo-Jing-Pan maar-diatreme volcanoes, indicating deep phreatomagmatic eruptions with less contribution to surface deposits. In addition, the explosion energy of the Ru-Huang-Ling maar with a diameter of 1900 m is about 7–8 times that of Luo-Jing-Pan maar with a diameter of 900 m.