The Mechanism And Genetic Model Of Vapor-liquid Circulation Processes In Changbai Mountain Two-phase Geothermal System

The formation of the Changbaishan geothermal system is mainly controlled by the subduction of the Pacific plate to the Eurasian plate.The study area is rich in geothermal resources,developing hot fumarole?up to 105°C?,gas-filled ground?40-60°C?,hot springs?20-82°C?and hydrothermal alteration.The premature research suggests that the genetic model of the liquid-phase geothermal system is difficult to explain the formation mechanism of D and ¹⁸O anomalies and the source of geothermal fluid replenishment,which also caused the failure of geothermal drilling in the later stage.The high-temperature fumarole is the main sign of the development of the two-phase geothermal system?vapor and liquid?.Combined with the recent drilling of high-Cl geothermal fluid,we considered there have vapor-liquid separation process token place in the lower part of Changbai Mountain by comparing with the typical geothermal field of the two-phase geothermal system developed at worldwide.Therefore,through the tectonic evolution,remote sensing reaction,earth exploration profile,geochemistry and isotope chemical analysis,the formation mechanism and internal fluid circulation characteristics of vapor and liquid are studied in based on two-phase geothermal system in Changbai Mountain area.There are six famous hot springs in the Changbaishan geothermal system,namely Jinjiang Hot Spring Group,Julong Hot Spring Group,Hubin Hot Spring Group,Shidaodaogou Hot Spring Group,Xianrenqiao Hot Spring Group and Laosandui Hot Spring Group,and have multiple geothermal In the production wells,the geothermal fluids are mainly HCO₃-Mg·Ca,HCO₃·Cl-Na,HCO₃·SO₄-Na and HCO₃-Na.The outlet temperature is between 25-82°C,and the gas from the source is not Contains soluble components such as HF,HCl and SO₂.It is known that the hot springs are mainly distributed in the inner part below 14km,and the surface thermal anomalies can be clearly identified through remote sensing by surface temperature inversion.Extraction of spectral curves of different hydrothermal alteration minerals?kaolin,sericite,chlorite,etc.?found that the fracture of Liudaogou Tianchi,Manjiang and Tumen River,four kilometers of fruit pine and Manjiang,Hongqi and four kilometers of fruit pine has a obvious alteration phenomena than others,and there are obvious temperature differences on both sides of the fault zone.The high temperature is mainly distributed on the side facing the crater.The field geological survey and the MT inversion profile indicate that the study area develops three types of geological structures:volcanic areas,sedimentary basin areas and bedrock exposed areas,and their geothermal matching elements?heat,reservoir,cap rock and water source?have significant differences.The heat source in the bedrock exposed area is the upper mantle conduction heat and high temperature magma gas.Its reservoir is the marble fracture zone and is recharged by karst water.The sedimentary basin area is the upper mantle conduction heat and radioactive heat generation,and the reservoir is Paleozoic limestone and Mesozoic clastic rock.The carbonate reservoir is replenished by ancient seawater and atmospheric precipitation;the heat source in the volcanic area is mainly from magma procket and high temperature magma gas,and the reservoir is the basalt,which is replenished by atmospheric precipitation and deep steam separated from the carbonate reservoir.The water chemistry,gas chemistry and B-Sr isotope analysis indicated that the bedrock exposed area was a liquid-dominate geothermal system,while the sedimentary basin area and the volcanic area were a two-phase geothermal system.According to the B-Sr isotope calculation model,the volcanic area is formed by the mixing of high-temperature condensate water and precipitation in the basalt reservoir,and due to hot magmatic volatile input,a secondary vapor-liquid separation taking place.In the clastic reservoir of the sedimentary basin is a result of mixing between high-temperature condensate water and precipitation in.The deep carbonate reservoir has a strong vapor-liquid taking place,of which 75%-87.5%of the ancient seawater has evaporated.The formation of bedrock exposed area geothermal system is related to karst water lateral migration in the marble fracture zone which heated by hot magmatic volatile input.In addition,based on the B isotope fractionation calculation,it was found that the lower part of Changbai Mountain has a new melt formation from the Pacific plate.Through the analysis of the current geothermal fluid exploit characteristics,we found that the deep reservoir has no additional fluid supply,or the secondary mineral blocked the the pores and prevents the water recharge.Combined with the typical geothermal phylogenetic characteristics worldwide,such as Geyeser in the United States and the geothermal field in Zhangzhou,China,we believed that as the depth of the magma procket of Changbaishan becomes shallower,ther hydrothermal geothermal system is gradually transforming into a dry-heat geothermal system.The deep dry hot rock and supercritical fluid geothermal resources are gradually becoming shallower,and this also means that the next volcanic eruption is approaching.