Geological Conditions And Distribution Law Of Geothermal System In The Basalt Area Of Changbai Mountain

Changbai Mountain is a complex volcanic mechanism with a trailing arc.It is located on the northern edge of the North China plate.Affected by the continuous subduction of the Pacific plate,Changbai Mountain is still active,providing a good prerequisite for the formation of geothermal.Due to the large-surface basalt cover in the study area,the internal structural features and stratigraphic distribution are unclear,which hinders the development of geothermal resources.This study takes the geothermal system of the Changbai Mountain area as the research object,deeply analysised it formation mechanism.According to the outcrop and newly drilled three geothermal wells,the underground thermal storage was mainly fault fault zone,Mesozoic clastic rock and Paleozoic carbonate rock.Affected by the new tectonic action,the influence of strata cutting is heavier,making the heat storage distribution appear fragmentary and there is no inner connection.However,the upper caps are all well developed,especially in basalt-covered areas,with an overall thickness of 5-1500m,which is a good cover.Under the background of the combination of the Helong block and the Longgang block,the entire study area can be divided into three different geothermal geological structures within the Neogene belt volcanism.The internal Cenozoic volcanic area,the central sedimentary basin area,and the external bedrock exposed area.The electrical structure of the neo-volcanic area is three-dimensional,the sedimentary basin is four-dimensional,and the outcrop area of the outcrop is a binary electrical structure.In this paper,the characteristics of geothermal geologic structure in different tectonic regions were established for the first time in combination with geophysical and outcrop features,in order to better constrain the formation mechanism of geothermal resources in the Changbai Mountains.The geothermal water supply in the study area is mainly recharged by atmospheric precipitation.The exposed hot spring water temperature is between 25°C and 82°C.It is affected by the lower magmatic gas and the upper formation.According to the B/Cl ratio,Piper and Schoeller diagram,it is found that the trend of geothermal water change in volcanic area and sedimentary basin is similar,mainly HCO₃-Na type water and its B/Cl ratio is lower than that of conventional volcanic rock B/Cl.Combined with the results of previous gas analysis,it is considered that the influence of the volcanic gas on it is affected.The geothermal water in the base rock outcropping area is similar to the surrounding karst water,and the concentration of the geothermal ion is low.It is presumed that it is the recharge of karst water.The B/Cl ratio also shows the influence of a certain volcanic gas,which is presumably formed by the heating of the volcanic gas.Finally,based on the geothermal geological structure model,combined with geothermal fluid geochemical analysis,we established the geothermal genetic pattern map in different tectonic zones,and developed 3 sets of geothermal systems:strip volcano type,stratiform basin type and banded structure modeling.At the end of paper,based on the inversion of temperature anomaly,the characteristics of geo temperature and geophysical characteristics,we predicted the favorable area of the Changbai Mountain geothermal system,and put forward 5 favorable target areas,in order to provide theoretical guidance for the rational development of the deeper geothermal resources.