共和盆地兰采温泉地区地热特征及干热岩靶区

Geothermal characteristics and hot dry rock target area in Lancai hot spring area of the Gonghe Basin

干热岩大力开发有助于我国“双碳”目标的尽早实现,其中放射性生热是干热岩形成的重要因素之一,研究该类型干热岩地质特征和放射性生热特征,对选择该类型干热岩勘查目标区具有重要价值和现实意义。为此,以共和盆地兰采温泉群地区为线索,通过野外地质调查、地表放射性伽马测量、岩石放射性测试等手段,研究了高温温泉形成的地热地质条件和放射性特征,并依据地球物理勘查解译数据初步圈定了干热岩勘查目标靶区。研究结果表明:(1)兰采温泉地区擦拉更复式花岗岩体和羊智河—夏琼断裂与兰采温泉群的形成关系密切;(2)该区出露的中晚三叠世斑状二长花岗岩、钾长花岗岩和斑状钾长花岗岩等岩体的生热率表现出异常高的生热率特征,是正常沉积盖层生热率的5~8倍;(3)基于大地电磁测深勘查解译,羊智河—哲格姜—夏琼断裂破碎带下伏低阻体,推测为侵入时代较晚、温度较高的“体中体”花岗岩体。结论认为,该区具有“体中体”地质结构的晚三叠世高放射性斑状钾长花岗岩体,可作为干热岩勘查的主要目标方向;下一步应查明复式岩体空间分布形态,研究复式花岗岩体与地热流体的关系以及对深部温度场的影响机理,进而为圈定干热岩勘查靶区提供更加确凿的依据。

Vigorous development of hot dry rock is helpful to the early realization of"dual carbon"goal in China.Radiogenic heat generation is one of the important factors for the formation of hot dry rock.The study on the geological characteristics and radiogenic heat generation behaviors of this type of hot dry rock is of great value and practical significance in selecting the exploration target area of this type of hot dry rock.Taking Lancai hot spring group area of the Gonghe Basin as the research object,this paper studies the geothermal geological conditions for the formation of high-temperature hot spring and its radioactivity characteristics by means of field geological survey,surface radioactive gamma measurement and rock radioactivity test.In addition,the exploration target area of hot dry rock is preliminarily delineated based on geophysical exploration interpretation data.And the following research results are obtained.First,Yanlageng complex granite mass and Yangzhihe-Xiaqiong fault are closely related to the formation of Lancai hot spring group in the Lancai hot spring area.Second,the heat generation rate of outcropped Middle-Late Triassic porphyritic monzogranite,moyite and porphyraceous moyite in this area is unusually high,which is 5-8 times that of normal sedimentary caprock.Third,magnetotelluric sounding exploration interpretation shows that the Yangzhihe-Zhegejiang-Xiaqiong fault fracture zone is underlain by a low-resistivity body,which is inferred to be a"body-in-body"granite mass with later intrusion and higher temperature.In conclusion,there is Late Triassic high-radioactivity porphyraceous moyite mass with a"body-in-body"geological structure in this area,which can be used as the main target direction of hot dry rock exploration.What's more,it is suggested to figure out the spatial distribution pattern of complex rock mass and research the relationship between complex granite mass and geothermal fluid and its influence mechanism on the deep temperature field,so as to provide an accurate basis for delineating the exploration target area of hot dry rock.