Estimation of Curie Depth of Subei Basin by Magnetic Anomaly

The Curie point depth is the depth at which the ferromagnetic mineral loses paramagnetism,which corresponds to a temperature of 550-580 degrees Celsius.This parameter is of great significance for constraining the thermal state of the lithosphere and can be used as an important reference for the evaluation of the prospects for dry hot rock exploration.We use aeromagnetic anomaly radial power spectrum based on the fractal magnetization model to calculate the Curie depth in the Subei Basin.We use the conventional method to preprocess the aeromagnetic data and process aeromagnetic data with selecting the appropriate wave number,domain,window size and fractal parameters to calculate the depth of the bottom of the magnetic source in the Subei Basin,which is approximated as Curie depth.The Curie depth of Subei basin ranges from 18 km to 37 km,with an average Curie depth of 23 km.The Curie depth of Baoying(20 km)and Jianhu(22 km)area is relatively shallow,and that of the surrounding area is relatively deep.In most areas,the Curie depth corresponds to the terrestrial heat flow.

Heat Flow Distribution and Thermal Mechanism Analysis of the Gonghe Basin based on Gravity and Magnetic Methods

Geothermal resource is indispensable as a clean, renewable, stable and cheap resource. Nowadays in China, the Gonghe Basin, located in northeastern Qinghai Province, has been thought to be a promising geothermal area. To explore geothermal energy potential in and around the Gonghe Basin, geophysical means including magnetic and gravity methods were used to plot distribution. Firstly, we inversed Moho depth and Curie point depth in and around the basin using gravity and magnetic data, respectively, through an improved Parker–Oldenburg algorithm. Secondly, seven different thermal models were established, considering radiogenic heat, basement depth, anomalous heat source and simulated corresponding temperature field and heat flow. These were analyzed numerically and we found the high heat flow in the Gonghe Basin coacted with radiogenic heat, an anomalous heat source and conductive heat. The distribution of seismic activities indicates that the Langshan–Wuwei–Gonghe Fault might have provided channels for transporting heat effectively.

Relationship between crustal magnetic anomalies and strong earthquake activity in the south segment of the China North-South Seismic Belt

The south segment of the China North-South Seismic Belt is located in the southeast margin of the Qinghai Tibet Plateau.This region is characterized by the frequent seismic activity in Chinese mainland.In this paper,the geomagnetic field model NGDC-720 and the data of terrestrial heat flow are used to investigate the distribution of crustal magnetic anomalies,the depth of Curie surface,and the characteristics of the crustal thermal structure in the south segment of the North-South Seismic Belt.The distribution characteristics of the vertical component AZ and the magnetic declination AD in the area with earthquakes over a magnitude of 6 and their aftershocks since 1970 are focused on.The results show that the earthquakes are mainly observed in the area of negative magnetic anomaly or the strong and weak transition zone.It especially shows in the AD.The Curie surface in the study area varies significantly,ranging from 20.8 to 31 km.The uplift area of the Curie surface is consistent with the high-value area of terrestrial heat flow.The high geothermal area corresponds to the strong earthquake activity area.The focal depth of most strong earthquakes is shallower than the depth of the Curie surface.The strong earthquakes mainly occur in the deep-shallow transition zones of the Curie surface.The results can be used as a reference for strong earthquake prediction in this area.

Study of the Geothermal Potential of the Locality of Kaladi and Its Surroundings (Adamawa-Cameroon) from the Frequency Processing of Magnetic Data

The aim of this study is to estimate the variations in curie point depth, geothermal gradient and heat flux from the frequency analysis of magnetic data in order to evaluate the geothermal potential of the Kaladi locality and its surroundings. For this purpose, the magnetic field map was first reduced to equator (RTE). The centroid method was used to divide the RTE grid into a set of 40 blocks. The spectral analysis applied to each block allowed determining the depth to top (Zt), center (Z0) and bottom (Zb also called curie point depth or CPD) of the magnetic sources. Knowing the different CPD, the geothermal gradient associated with each block was calculated. The heat flow was then calculated from the geothermal gradient associated with the anomaly block considered. From the set of values obtained for each block, maps of geothermal gradient and heat flow variations were established. Analysis of these maps shows that the sectors that could be favourable for geothermal exploration are the north of Kaladi and the Goro-Bembara corridor, because they show variations in the geothermal gradient and heat flow between 0.4 and 0.8℃/m and between 1.2 and 2 mW/m2 respectively. In addition, the superposition of the different hot springs highlighted in previous studies with areas of high geothermal gradient and heat flow values supports this analysis. The proposed models can be used as background documents for any geothermal exploration project in the study area.

Distribution of Helium Resources in Weihe Basin,Central China:Insight from 3D Magnetic Inversion

There is promising indication of helium-rich natural gas in Weihe Basin.However,the lack of a detailed investigation on the origin and the spatial distribution of helium source rocks(mainly Yanshanian granites)limits the helium potentiality evaluation in Weihe Basin(WB).We performed three-dimensional(3 D)inversions of magnetic data in Weihe Basin and its adjacent areas to figure out the crustal thermal structure and the temporal-spatial distribution of deep granite in the basin.Based on this,we have proposed a geological model of helium accumulation and predicted the potential area of helium distribution.The results of 3 D magnetic inversion indicate that the granites in the deep Weihe Basin are mostly located at the central and southern parts of the basin,which are connected spatially with the granites in the North Qinling Orogenic Belt.These granites were all derived from largescale intra-continental orogeny in the Qinling area during the mid-Mesozoic,providing a good material basis for crust-derived helium in the basin.The local uplift of the Curie surface makes the thermal fluid more actively,which contributes to helium accumulation.The faults developed in the WB are the migration pathway of crust-derived helium and the upward migration of the mantle-derived helium.The wells with high percentage helium are mostly located near the Weihe fault and the areas on the south of it.The Wugong-Xi’an-Lantian area in the central and the Lintong-Weinan-Tongguan area in the eastern Weihe Basin are the most promising helium distribution areas.Furthermore,the region from the north of Taibai Mountain to Baoji City in the western Weihe Basin may also be another potential area of Helium resource.

Investigation of geothermal structure of the Sulawesi,using gravity and magnetic method

The Sulawesi Sea and Sulawesi Island are located in the western Pacific area where volcanic activity,plate subduction,and seismic activity are very active.The Sulawesi basin formed during the Middle Eocene-Late Eocene and nearly half of the Eocene oceanic crust has subducted below the North Sulawesi Trench.The Sulawesi Island was spliced and finalized in the Early Pliocene-Pleistocene during volcanic activity and is recently very active.This area is an optimal location to study volcanic geothermal conditions and subduction initiation mechanisms in the southern part of the western Pacific plate margin,which are important in geothermal and geodynamic research.In this study,we combined 133 heat flow data with gravity and magnetic data to calculate the Moho structure and Curie point depth of the Sulawesi Sea and periphery of the Sulawesi Island,and analyze the distribution characteristics of the geothermal gradient and thermal conductivity.The results show that the average depths of the Moho and Curie surfaces in this area are 18.4 and 14.3 km,respectively,which is consistent with the crustal velocity layer structure in the Sulawesi Basin previously determined by seismic refraction.The average geothermal gradient is 4.96°C(100 m)-1.The oceanic area shows a high geothermal gradient and low thermal conductivity,whereas the land area shows a low geothermal gradient and high thermal conductivity,both of which are consistent with statistical results of the geothermal gradient at the measured heat flow points.The highest geothermal gradient zone occurs in the transition zone from the Sulawesi Sea to Sulawesi Island,corresponding to the spreading ridge of the southward-moving Sulawesi Basin.Comprehensive gravity,magnetic,and geothermal studies have shown a high crustal geothermal gradient in the study area,which is conducive to the subduction initiation.The northern part of the Palu-koro fault on the western side of Sulawesi is likely the location where subduction initiation is occurring.During the process of moving northwest,the northern and eastern branches of Sulawesi Island have different speeds;the former is slow and the latter is fast.These branches also show different deep tectonic dynamic directions;the northern branch tilts north-up and the eastern branch tilts north-down.