摘要
Low-medium temperature geothermal system of convective type has a very important significance in clarifying the regional tectonic activity,the formation of geothermal resource,as well as water-rock interaction and useful element enrichment mineralization. Water as a heat carrier,its isotopic variation is the premise for studying water-rock interaction and tracing the source of geothermal water. In this article,we have gathered 167 δD data in geothermal water and local cold spring water in China. Then,we overlay the location of geothermal field on the regional active fault system in order to figure out the spatial relationship between geothermal spring and regional active fault.The results show that 1) 91.11% of geothermal water locates near the Quaternary fault; 2) δD value of geothermal water is lower than local cold spring water. This δD variation is further studied in this article. According to kinetic fractionation theory,this phenomenon is caused by the H-D isotopic fraction in water during water recycle in the crust.The mechanism is a process that separates H-D isotopes from each other by their mass during unidirectional processes(water circulation),while the degree of fractionation is dependent on temperature and the routine length. For convection geothermal systems in active tectonic zones,there are plenty of fractures and fissures. In this way,water can make deep circulation in convection geothermal system. During the circulation,the H-D isotopes can gather enough heat quantity and enough routine to fraction. On the basis of above analysis,we have modeled the geothermal water H-D fraction in convection geothermal systems as raised by White(1968).As a secondary reason,the H-D isotopic exchange between water and kaoline/montmorillonite can also reduce the δD in geothermal water.
