广东神灶海上温泉的流体地球化学特征及循环模式

Geochemical Characteristics and Circulation Conceptual Model of Geothermal Fluid in the Shenzao Coastal Hot Springs in Guangdong Province

广东神灶温泉出露于海水之中,揭示其流体循环机制对地热资源的可持续开发利用具有重要意义.通过采集神灶温泉区地热水、地热气体和海水样品,测试其流体地球化学组成及主要同位素组成,得到以下认识:神灶温泉水化学类型为Cl-Na·Ca型,主要由大气降水补给;水中盐分主要来自硅酸盐矿物溶解和现代海水混入,海水混入比例为29%~32%.利用化学温度计估算热储温度为130℃,地热水循环深度约4 km.地热气体以大气起源N_(2)为主要组分,CO_(2)、CH_(4)为壳内有机沉积物的热变质产物.此外,He同位素指示幔源组分占比不足5%,研究区大地热流值为67~69 mW/m^(2).综上,神灶温泉区是以壳内放射性生热为主要热源的中温对流型地热系统.

Shenzao hot springs are exposed in seawater and it is significant to reveal the circulation mechanism of geothermal fluids for the sustainable development and utilization of geothermal resources.By collecting samples of geothermal water,geothermal gas and the seawater,and testing the chemical and isotopic compositions of the samples,this study draws the following conclusions:the hot spring water is of Cl-Na∙Ca type,recharged by the precipitation;the dissolved constituents are mainly derived from the dissolution of silicates and mixture with the seawater,with a mixing ratio of 29%−32%.According to the hydrochemical geothermometers,the reservoir temperature is 130℃,implying a circulation depth of 4 km.The atmospheric-derived N_(2)is the dominant component in geothermal gas and the CO_(2),CH_(4)are thermogenic products of the crustal organic sediments.In addition,the helium isotopic compositions suggest that the mantle contribution is less than 5%and the local heat flow value is about 67−69 mW/m^(2).Therefore,the Shenzao geothermal system is a medium-temperature convective system mainly heated by the crustal radiogenic heat source.