Geothermal structure revealed by curie isothermal surface under Guangdong Province,China

Guangdong Province in Southeast China is noted for its numerous geothermal resources due to tectonic episodes,mainly occurred during the Cretaceous.The surface heat flow and geothermal gradient are the most direct ways to understand the temperature of the Earth.However,geothermal resources are poorly utilized in Guangdong Province due to limited numbers of boreholes and surficial hydrothermal fluids.To improve the understanding of underground temperature distribution in Guangdong Province,we have applied power-density spectral analysis to aeromagnetic anomaly data to calculate the depth of the Curie isothermal surface.Upward continuation is applied and tested to the magnetic data.The calculated Curie isotherm is between 18.5 km and 25 km below surface.The fluctuation in the depth range reflects lateral thermal perturbations in the Guangdong crust.In particular,the eastern,northern,western and coastline areas of the province have a relatively shallow Curie isotherm.By comparing the surface heat flow,geothermal gradient,distribution of Mesozoic granite-volcanic rocks,and natural hot springs,we conclude that during Mesozoic,magmatism exerted great influence on the deep thermal state of Guangdong Province.A shallow Curie isotherm surface,as well as numerous natural hot springs and high heat flow,show clear signatures of shallow heat sources.

Investigation of Curie Point Depth in Sulu Ultrahigh-Pressure Metamorphic Belt,Eastern China

The Curie point depth of continental crust can reflect the regional tectonic pattern and geothermal structures. Analysis of magnetism is an efficient way to obtain the Curie point depth on a regional scale. This study systematically investigated the Curie point depth of Sulu （苏鲁） ultrahigh pressure （UHP） metamorphic belt （33°40＇N to 36°20＇N and 118°E to 120°E, ca. 60 000 km^2）, eastern China using aeromagnetic data. The results show that the Curie point depth of the Sulu region varies from 18.5 to 27 km. The shallowest Curie point depth （ca. 18.5 km） is located in Subei （苏北） subsidence, where the estimated temperature gradient value is about 31.35℃/km, which is comparable with the measured value of 30 ℃/km. In addition, a two-dimensional numerical solution of the heat conduction was used to calculate the temperature field to a depth of 30 km along the profile from Tancheng （郯城） to Lianshui （涟水） with a length of 139 km. The steady state model solved using the finite element method shows that the temperature around the Curie point depth is about 585.36 ℃, which is close to the Curie temperature （580℃） of magnetite at atmospheric pressure. These results provide new insights into the tectonic and continuous thermal structures of the Sulu UHP metamorphic belt.

Postrift Rapid Subsidence Characters in Qiongdongnan Basin,South China Sea

In this article,the backstripping technique was used in studying the subsidence charac-ters of the Qiongdongnan（琼东南） basin（QDNB） in order to understand its dynamic mechanism of formation and evolution.Meanwhile,the geothermal characteristics of this area were summarized,and the stretching factors（β） of the upper crust,the whole crust,and the whole lithosphere were calculated.The QDNB is characterized by high subsidence rate,high geothermal gradient,high geothermal heat flow,and the lithosphere stretching and thinning of this area are depth dependent.An asthenosphere zone must have been confined under the lithosphere of Southeast Asian continent because of the mutual subductions of the Eurasian plate,the Pacific plate,the Indian-Australian plate,and the Philippine Sea plate.These characters indicate that strong mantle convection occurred and the lower crust materials flowed away in the domain,which lead to the rapid flexural isostasy subsidence of the upper crust and the uplift of the asthenosphere.

Hydrothermal interactions in energy walls

Energy geostructures(EGs)employ heat exchangers embedded in concrete geostructures,such as piles,walls,tunnels,and sewers.In this study,energy walls(EWs)are studied with an emphasis on the following objectives:(1)to understand the fundamentals of hydrothermal interactions acting in the vicinity of EWs caused by groundwater seepage in saturated soil;(2)to highlight hydraulically induced thermal effects and their consequences on the thermal performance of EWs.Extensive three-dimensional hydrothermal finite element analyses are performed considering two groundwater flow conditions:perpendicular and parallel to the EW.The thermal activation of the geostructure locally modifies the flownet with respect to the non-isothermal case because of the temperature dependency of the water properties.Mutual interactions between seepage directions and thermal activation are analyzed.Remarkable thermal interactions are detected within the heat exchangers.The thermal behavior of EGs is highly affected by an incorrect evaluation of the hydraulically induced thermal effects,which may result in an overestimation of the thermal behavior.Conversely,an efficient thermal design,which considers such interactions,may increase the thermal potential of EGs.