云南省洱源县断裂特征及其对地热的控制作用

Characteristics of faults and their controlling effect on geothermal energy in Eryuan county,Yunnan Province

地热资源在未来的能源结构中具有重要地位,为分析云南省洱源县地热资源分布的构造控制因素,文章通过野外地质调查对县域内多条重点断裂进行了野外露头观测和分析,对不同断裂类型两盘受力情况进行计算和分析,并通过三维立体图形对县域内断裂与地热分布进行了展示,结果表明:洱源县域内发育多条大型断裂带,走向以NW−SE向为主,具有多期构造活动,具“压扭性”或“张扭性”特征,并被后期张性断层切割改造;正断层下盘及逆断层上盘具有更大的正应力值和剪应力值,多发育牵引背斜,更容易发育裂缝;断裂构造对温泉的控制作用明显,其中大型走滑断裂可沟通深部热源,温泉热水可沿后期张性断裂发生地下径流,然后可在断裂附近的裂缝发育带、断裂交汇处以及断层尖灭处聚集区,在海拔及第四系等多因素综合影响下,热水出露地表形成温泉。

As a kind of green and clean energy,geothermal resources are new and renewable and play an important role in the future energy frame.Due to the unique tectonic location and intense fault activities,there exist favorable geological conditions for the formation and flow of geothermal water in Yunnan Province,especially in its western area,so geothermal resources are very rich.In order to analyze the structural factors of the distribution of geothermal resources in Eryuan county,Yunnan Province,this study focuses on two basic topics of the structural characteristics and fracture development mechanism of the key fault zones in Eryuan county,and selects several hot springs as research objects in Sanying town,etc.Through field geological surveys,this study calculates the stress-strain properties of different faults and predicts the fracture distribution under the background of different faults and multiple fault combinations,based on which a three-dimensional spatial model of the fault structures and hot springs in the study area has been established,showing the spatial relationship between the faults and geothermal energy in the county.The study results on the faults show that there are many large fault zones developed in Eryuan county,mainly including Weixi-Qiaohou fault,Longpan-Qiaohou fault,Luopingshan fault,Heqing-Eryuan fault,Nandaping fault,Beipai-Zhengshengcun fault,etc.The fault trend is mainly NW-SE,with characteristics of multi-stage tectonic activity.Many scratches,steps and structural breccia can be found in the field,with obvious"compression-torsional"or"tension-torsional"characteristics.Several faults are cut and transformed by late tensile faults,and have typical"flower structure"on the cross sections.On the plane,the tectonic deformation in the west of the Beipai-Zhengshengcun fault is mainly ductile-brittle deformation in early tectonic uplift period.The area to the east of this fault is mainly brittle deformation,and the Neo-tectonic movement is manifested by obvious tectonic performance.The theoretical calculation results show that the footwall of normal faults and the hanging wall of thrust faults have large normal stress values and shear stress values.During the formation and evolution of the faults,the two strata mostly form tractive anticlines,and the top of these anticlines are generally in an extensional stress state.Under the effect of gravity and other stresses of the overlying strata,the footwall of normal faults and the hanging wall of thrust faults are more likely to develop fractures near the faults,providing geological space for the flow or accumulation of hot spring water.The analyses of the distribution of surface hot springs in Eryuan county show that the hot springs are mostly distributed in the areas with favorable fractures.The hot springs in Niujie town in the north of Eryuan county are located in the hanging wall of Heqing-Eryuan(thrust)fault zone,and at the intersection of late extensional faults.The outcrops of these hot springs are at relatively low altitudes.The hot springs near Eryuan county are located at the hanging wall of thrust fault(i.e.Beipai-Zhengshengcun faults),the arc turning of the fault,and the plane intersection of the NE secondary fault and the main fault.The hot springs in Sanying town are located at the intersection of Nandaping fault and multiple sets of normal faults in the northeast direction,at the foot wall of Nandaping fault at a relatively low altitude.A number of hot spring outcrops on the west side of Yousuo town are in beaded distribution on the plane,consistent with the north-south strike-slip faults(i.e.,the Xunjiancun fault),and are located at the middle and south ends of the strike-slip faults,both of which are the intersection of the strike-slip faults and the north-east faults.To sum up,faults have an obvious control effect on the hot springs in Eryuan county.The big cutting depths of large strike-slip faults are conductive to the communication of the deep heat source.That is to say,as important channels for the upwelling of deep magma,these faults are geologically manifested that a number of magmatic intrusions or veins are distributed along strike-slip faults,with relatively high geothermal gradients.In the later stage,a large number of tensile faults are developed,generally in the northeast direction.Most of them are"open",and some of the transverse sections of the faults can be characterized by V-shaped structures.Hot spring water can generate underground runoff along the tensile faults.Since the footwall and hanging wall of the normal faults can be classified as fracture development zones,hot springs can be concentrated in these fracture zones,at the intersection of faults with different directions and at the pinch-outs of faults.Under the comprehensive influence of multiple factors such as altitude and Quaternary,hot water is exposed to the surface to form hot spring spots.