Assessing magmatic contributions to rift-related geothermal systems in collisional orogens: Insights from the Sangri-Cona rift, southern Tibetan Plateau

Abstract

Fault-controlled geothermal systems in the Himalayan-Tibetan orogen could receive heat and material from deep-seated magmas due to crustal anatexis in orogenic settings. The near N-S trending rifts in southern Tibetan Plateau host abundant geothermal systems but potential role of residual magmas remains less constrained. Here, we evaluate magmatic contributions to geothermal systems in Sangri-Cona rift (SCR), the youngest rift in southern Tibetan Plateau, based on chemical and isotopic compositions of thermal waters from a south-to-north sampling profile. Our results show that the thermal springs in the central SCR have significant inputs from magmatic fluids, which account for high B concentrations and positive shift in δ18OH2O, while those in the southern and northern SCR are dominated by recharge of meteoric water. Water-rock interaction constrained by 87Sr/86Sr, hydrochemistry, and geothermometry results, suggests a hotter or deeper groundwater circulation path beneath central SCR than that of the southern and northern SCR. The identified magmatic fluid inputs, higher reservoir temperature, and higher degrees of water–rock interaction in the central SCR agree well with the presence of high conductivity anomalies at crustal depths of ∼ 10–30 km revealed by magnetotelluric surveys. Our findings provide geochemical evidence for the impact of lithospheric extension and associated geological and geophysical expressions (e.g., extension-induced exhumation of genesis domes that recorded crustal anatexis and upwelling of partially molten crustal channel flows) on modern geothermal systems in collisional orogens.