Three-dimensional electrical structure model of the Yangbajain geothermal field in Tibet:Evidence obtained from magnetotelluric data

The Yangbajain Geothermal Field in Tibet is located in the fault subsidence basin of the central Yadong-Gulu Rift Valley.The spatial distribution of the field is controlled by mountain-front fault zones on the northwestern and southeastern sides of the basin.Geothermal power has been generated in Yangbajain for more than 40 years.However,owing to the lack of threedimensional(3D) geophysical exploration data,key geological issues related to the partial melt body of the Yangbajain Geothermal Field,such as its location,burial depth,and geometric form,as well as the ascending channel of the geothermal fluid,have for a long time been controversial.In this study,3D inversion was performed using measured geo-electromagnetic total impedance tensor data from 47 survey points.The extracted horizontal sections at different depths and profiles,and at different lines,reflect the 3D electrical structure model of the geothermal field in the study area.Subsequently,three findings were obtained.First,the partial melt body,located below the China-Nepal Highway extending along the northeast direction,is the heat source of the Yangbajain Geothermal Field.The burial depth range of the molten body was determined to range between approximately 6.2 and 14 km.Moreover,the geothermal fluid ascended a horn-shaped circulation channel with an up-facing opening,located in the northern section of the sulfur ditch area.The study results revealed that deep rock fissures(>2 km) were not well developed and had poor permeability.In addition,no layered heat reservoirs with high water richness were observed in the northern part of the study area.However,the application of enhanced geothermal system(EGS) technology in the northern region would be essential to improving the power generation capacity of the Yangbajain Geothermal Field.In addition,the study found no deep high-temperature heat storage areas in the southern region of the study area.

地质参数对中深层地热井长期取热特性影响分析

基于中深层地热井换热原理,数值分析不同地质参数下中深层地热井在长期运行过程中单井取热量、能效系数、热泵机组COP以及岩土温度的变化情况。研究结果表明:岩土导热系数对长期运行期间的单井取热量、能效系数的下降比例影响较大,且岩土导热系数越小其下降比例越大。岩土导热系数为2.0 W/(m·K)时,第30年的单井取热量、能效系数与第1年相比均下降13.7%。地温梯度对长期运行期间的热泵机组COP的下降程度有较大影响,其下降比例随地温梯度的增大而增大。此外,不同地质参数下岩土温度影响半径随运行年份增加的比例一致。

The uplifting and denudation of main Huangshan Mountains,Anhui Province,China

The Huangshan Mountain Geopark is an important geological landmark and tourist attraction.In this paper,we apply fission track dating to examine the uplift and exhumation processes that created the Huangshan Mountains and provide a timeline for their development.In addition to being an important scientific contribution,this information can be used on guided tours and to promote tourism.The results of eight apatite fission-track analyses suggest three age groups:56,45-30,and 15 Ma.These age groups are related to the uplifting-erosion processes involved in forming ancient multilevel denudation planes at 85-50,45-30,and 24-5 Ma,respectively.The scenic area has experienced three stages of thermal evolution.The first stage occurred before 80 Ma and the third stage after 13 Ma.The three stages had varying cooling rates:2.69,0.62,and 4.23°C/Ma,respectively.Uplifting rates also varied:0.08,0.02,and 0.12 mm/a.The uplifting ranges were also variable:1.14,1.57,and 4.00 km,respectively.Significant uplifting differences between diverse areas are obvious and there were four magnitudes of cumulative uplifting range:4060-3950,3760-3490,3190-3070,and 2650 m.The surface uplifting range varied from 450 to 2230 m.Denudation and uplifting amount averaged 2340 and 3400 m,respectively.The 1060 m difference between them is the average elevation at present.