Thermo-rheological structure of the lithosphere in Hainan Island, Southeast China and its geothermal significance

Abstract

Based on heat flow, seismic wave velocity, and rheological parameter data, this study constructs a thermo-rheological model of the lithosphere beneath Hainan Island, China. Using this model, we have determined the thermal structure, thermal lithosphere thickness, and rheological structure of the lithosphere beneath Hainan Island. The results indicate a “cold crust, hot mantle” thermal structure, with mantle heat flow ranging from 49 to 58 mW/m², contributing over 65 % of the total heat flow. Hainan Island exhibits a relatively thin thermal lithosphere that gradually thickens from north to south, and characterized by a high surface heat flow with corresponding changing trends. The rheological structure of Hainan Island follows a “brittle-ductile–brittle-ductile” pattern, characteristic of a “strong crust and weak mantle” configuration. Our analysis suggests that the high thermal state/condition and unique thermo-rheological structure of Hainan Island are closely related to the geodynamic background of Pacific plate subduction and the upwelling of the Hainan mantle plume. This upwelling has led to the formation of a high-temperature anomaly zone in the upper mantle beneath the island. Additionally, the thermal structure of the lithosphere significantly controls its rheological strength, with terrestrial heat flow influencing the regional strength of the lithosphere.