雄安新区地热水化学特征及其指示意义

Hydrogeochemistry of Geothermal Waters from Xiongan New Area and Its Indicating Significance

地热流体水文地球化学研究是认识地热资源形成机制、赋存环境以及循环机理的有效手段.以我国华北平原典型的中低温地热系统——河北雄安新区为研究对象,基于不同热储层和浅层地下冷水的水化学及同位素特征,探讨地热流体中主要组分的地球化学起源,评估深部地热流体的热储温度,指示地热系统的深部热源及其成因机制.大气降水入渗、热储高温条件下的流体-岩石相互作用是雄安新区地热流体中主要组分的物质来源,其中深层雾迷山组地热水中部分组分可能源于古沉积水蒸发浓缩过程中形成的蒸发岩盐的溶滤.雾迷山组地热水适宜利用Ca-Mg温标和石英温标计算其热储温度,温度范围为76.4~90.6℃,馆陶组地热水运用石英温标更为合理,热储温度为66.2~71.3℃.雄安新区地热异常是深部放射性元素衰变热在特定的大地构造背景下聚集而形成.

Hydrogeochemical reaserch of geothermal fluids is an effective method to understand the formation mechanism,occurrence environment and circulation process of geothermal resources. Xiongan New Area, one of the typical low-temperature geothermal systems in the North China plain, is selected as the study area. In this study it is based on the analysis of water chemistry and isotopes, and aims:(1) to discuss the geochemical origin of main components in geothermal fluids,(2) to estimate the deep reservoir temperatures of geothermal waters,(3) to figure out the heat source beneath geothermal area and its genetic mechanism. The hydrochemical evidences imply that the main components in Xiongan geothermal waters are contributed by meteoric waters input and intense fluid-rock interactions at high reservoir temperatures, and several components of Wumishan Formation geothermal waters are from the dissolution of evaporation salt formed during the diagenetic process. The Ca-Mg and quartz geothermometer are suitable for estimating the reservoir temperature of Wumishan Formation geothermal waters, while that for Guantao Formation geothermal waters, the quartz geothermometer is much more appropriate. The calculated temperatures range from 76.4 to 90.6 ℃ and 66.2 to 71.3 ℃, respectively. The geothermal anomaly beneath Xiongan is likely to result from decay of radioactive elements in a specific tectonic setting.