A conceptual model of the Tianjin geothermal system based on isotopic studies

The isotopic technique is an effective measure to set up the conceptual model of a hydrothermal system. A deep circular geothermal system exists in Tianjin, including the semi-open and semi-closed karst geothermal subsystem in the bedrock and closed porous water subsystem in the clastic rocks. The geothermal water is originated from the ancient precipitation of 21-10 kaBP. Since Holocene epoch, the geothermal water is sealed for heating up. The mainly feeding channels are the karst conduits in weathered carbonate rocks of Proterozoic and Lower Paleozoic.