Deep thermal state on the eastern margin of the Lhasa-Gangdese belt and its constraints on tectonic dynamics based on the 3-D electrical model

Abstract

Since the Mesozoic, the Lhasa-Gangdese block has undergone several stages of tectonism-magmatism caused by the closure of the New-Tethys Ocean and the collision between the Indian and Eurasian plates, which led to the lithospheric shortening and crustal uplift. Through the careful processing and analysis of the magnetotelluric data on the eastern margin of the Lhasa-Gangdese block near 92°E, a reliable 3D electrical model was obtained to examine the relationship between the lithospheric electrical structure and geodynamics. Some conductive and resistive layers were obtained, which may be formed in some tectonic processes. The thermal model of the lithospheric uppermost mantle (75–100 km) were calculated using the Arrhenius equation and the Hashin-Shtrikman (HS) boundary condition. Combined with the terrestrial heat flow point and curie isothermal in the study area, the temperature distribution at the 30–100 km depths was calculated. The melt fractions of the mid-lower crust calculated by the classical Archie's law, pressure calculated by density and temperature at different depths can be obtained in a meantime. The resistor beneath the Tethys-Himalaya terrane represented the subduction of the Indian plate with a deep angle. The subduction of the Indian crust may not exceed the Indus-Yarlung Zangbo suture, while the Indian lithospheric mantle may not reach the Luobadui-Milashan fault. Additionally, our electrical and thermal structure indicated that the Indian lithospheric mantle probably detached from the Indian crust. Our study further discussed the underplating of the mantle-derived materials and the southern extrusion along the Main Himalaya Trust, and offered a subsidiary evidence for the possible “south-eastward crustal flow” in a local area. Finally, the relationship between the electrical structure and the deep metallogenic mechanism was briefly established.