重庆温泉及地下热水的分布及成因

Occurrence and formation of the hot springs and thermal groundwater in Chongqing

重庆地区地下热水资源较为丰富,且地下热水的分布也比较特殊。着重对重庆温泉及地下热水的分布特征、水化学特征、热储构造、形成条件和成因模式等问题进行了总结。重庆附近地下热储为三叠系中、下统碳酸盐岩,地下热水的分布受到背斜构造控制,温泉大多在高隆起背斜轴部、两翼及倾末端出露,与常见的受断裂控制的断裂-深循环型地下热水的分布不同,属于盆地-出露型的地下热水分布类型,水温为32~64℃,属于中低温温泉。受背斜构造的影响,地下热水主要溶滤三叠系中、下统雷口坡组和嘉陵江组碳酸盐岩,TDS为2~3 g/L,水化学类型多为SO_4—Ca型,长期溶滤作用使地下热水趋于淡化,但尚未达到淡水阶段。地下热水热源主要为正常的地热增温,大气降水为其补给来源,补给区高程约为670~1 500 m。大气降水在重庆各背斜核部岩溶露头区入渗,地下水沿着背斜两翼向热储层深部径流并获得加热后,顺构造线方向自南、自北向背斜中部或向背斜倾末端径流,在河流深切的峡谷地段碳酸盐岩裸露区或埋藏区出露成泉,或在背斜两翼人工揭露形成钻井温泉和坑道温泉。

Thermal groundwater resources in Chongqing are relatively abundant and the occurrence of the geothermal water is unique. In this paper, the occurrence, hydrochemical features, geothermal reservoir structure, formation conditions and genetic modes of the thermal groundwater in Chongqing are described. The geothermal reservoirs consist of the Lower and Middle Triassic carbonates. The occurrence of thermal groundwater in Chongqing is controlled by anticlines and is different from that of the common fault-deep circulation controlled by faults. The hot springs mainly exist in the axis, the two flanks and the plunging end of the anticlines. The type of geothermal water occurrence is of the basin-outcropping type. The temperature of the hot water ranges from 32 ℃ to 64 ℃ and the hot springs are of middle-to-low temperature water. Affected by the anticline structures, incongruent dissolution of the carbonates of the Lower Triassic Jialingjiang and Middle Triassic Leikoupo Groups occur. The TDS of the geothermal water are 2 - 3 g/L and hydrochemical types are mainly of SO4-Ca type. The hot water tends to be fresh owing to the long-term incongruent dissolution of the carbonates, but has not yet reached the freshwater stage. The geothermal water receives heat from the normal heat flow and is of meteoric origin. Groundwater receives recharge from precipitation in the recharge areas （i. e. , the outcropping areas of the carbonates in the cores of the anticlines with elevation of approximately 670 - 1 500 m）, flows along the carbonates in two flanks of the anticlines to the deep parts. After heated, the hot water flows along the anticlines from both north and south to the middle parts of the cores or to the plunging ends of the anticlines and issues in the form of the hot springs. Geothermal wells and tunnels also reveal hot water in the two flanks of the anticlines.