Integrated mechanisms of geothermal anomalies in the eastern Himalayan syntaxis: Insights from crustal partial melting and fault-controlled fluid circulation

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Study region The eastern Himalayan syntaxis (EHS) in eastern Qinghai-Xizang plateau. Study focus As the forefront of India-Asia collision, the EHS demonstrates the rapid uplift since the late Miocene, which features multi-stage active structural development and widespread distribution of highly active hydrothermal activities. This study provides novel insights on the integrated mechanisms of geothermal anomalies of EHS within the context of multi-stage regional uplift, which reveals hydrochemical control factors, migration processes, heat-controlling structure, and deep thermal structure in EHS. New hydrological insights for the region Geophysical and thermometric analyses reveal that the crustal partial melting domains at 13–17 km depth beneath the EHS, served at the principal heat source for the geothermal anomalies of EHS. The concentric high-angle normal fault centered around the Namche Barwa peak provides upflow and discharge pathways for geothermal waters in EHS, which identified into six ascending cooling processes and three structural control modes. The geothermal waters in EHS were classified into three hydrochemical types: HCO 3 -(SO 4 )-Ca/Na, SO 4 -(HCO 3 )-Na/Ca, and Cl-(HCO 3 )-Na. δD and δ 18 O isotopes suggest that geothermal fluids were primarily recharged by meteoric water, with magmatic contributions. The composition of geothermal water in EHS was dominantly controlled by dissolution of silicate minerals. Reservoir temperatures (77.6–254.5 ℃) and mixing ratios (6.27–97.97 %) exhibit significant variations in thermal springs. With the content of multi-stage uplift, the genesis model of geothermal fluid was systematically constructed.

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