Evolution of Middle-Low Temperature Carbonate Geothermal System in Taiyuan,Northern China

To study the complicated issue of interactions between carbonate geothermal system with mid-low temperature existing in Taiyuan basin and its surrounding karst system existing in mountains,the geological evolution processes of the carbonate geothermal system were remodeled based on the analysis of geological structure and characterization of hydrochemistry and isotopic compositions of the karst water.We come to the following conclusions:(1) The carbonate geothermal system with mid-low temperature has experienced five stages of geological evolution since Yanshan Movement.and it separated from its surrounding karst system in mountains during the stable sedimentation period of Neogene to the Early Pleistocene,and then they evolved respectively;(2) The karstification of the carbonate geothermal system with mid-low temperature were due to the following two factors:① rainfall of the late Middle Pleistocene and the early Late Pleistocene infiltrated along the fault zone(e.g.Fenhe fault),reacted with the metal sulfide in C-P coal measure strata and formed the groundwater rich in sulfuric acid.The groundwater was recharged to the carbonated geothermal reservoir and mixed with the older karst water stored in it,which facilitated the dissolution of carbonate rock;② the pyrolyzation of carbonated rock occurred by the baking of magma from the basin basement in the late Middle Pleistocene and the early Late Pleistocene;(3) The karst water in the geothermal system formed in the late Middle Pleistocene and the early Late Pleistocene,and sealed up to now because of the good insulation of its overlying strata.Mainly controlled by the geological structure,its east-west boundaries were Dongshan fault and Xishan fault respectively and its south-north boundaries were Tianzhuang fault and north boundary of Qinxian horst respectively.