Role of crustal radiogenic heating in ultra-high temperature metamorphism of the Greater Himalayan Crystalline complex: Phase equilibrium and numerical modelling

Abstract

Ultra-high temperature (UHT) metamorphism is a significant feature of the Greater Himalayan Crystalline complex (GHC), which constrains the dynamics of continental subduction and subsequent continental collision. However, the mechanism of such kind of UHT metamorphism is widely debated, including slab tearing-induced mantle upwelling, mechanical heating, radiogenic heating, and others. To better understand the UHT metamorphism and the thermal budget of collisional orogens, we first conduct a forward phase equilibrium modelling coupled with geochemical modelling to explore the variation of radiogenic heat production (RHP) of felsic melt, indicating that it may range from 4 μW/m3 to 9 μW/m3. Then, we incorporate the variable RHP into a thermo-mechanical model to study its effect on the thermal evolution of the collision zone. The numerical models reveal that a reasonably increased radiogenic heat production of 4 μW/m3 for the partially molten felsic crust contributes to UHT metamorphism after the continental collision for 30–35 million years. The model results are consistent with the structural observations, geochemical signatures, and P-T paths of the GHC. After the comparison with other mechanisms (e.g., the effects of mechanical heating and anomalous mantle heating), we propose that radiogenic heating could be a predominant heat source for the rapid UHT metamorphism of the GHC, whereas mechanical heating and heat flux from the mantle play secondary roles.