Exploring a long distance, amagmatic, across-suture orogenic geothermal system: Sri Lanka’s foreland hot springs

Hot springs in orogenic geothermal systems are usually within 5-15 km of the recharge zone, either within the mountain range or along the mountain front. However, in Sri Lanka, hot springs are in the foreland up to 100 km away from their recharge zones in the Highland Complex. The absence of a sedimentary cover provides the opportunity to study fluid pathways along basement faults and fractures. We identify a fracture network that connects the recharge and discharge zones oriented 015°-090°. Its orientation to the regional stress field indicates that the majority of the faults and fractures are permeable to allow fluid transport. With a geothermal gradient of ∼20°C/km obtained from 1D modeling, the estimated maximum circulation depth of the hot spring water is 3.5-5 km. Such foreland geothermal systems may also occur in other parts of the world hidden under a sedimentary cover, which could provide an immense geothermal resource.