Curie Point Depth Research Articles

Piezomagnetic fields associated with a dislocation source in a layered elastic medium

SUMMARYThe piezomagnetic effect is defined as a change in magnetization with applied stress. Changes in the geomagnetic field caused by the piezomagnetic effect, referred to as the piezomagnetic field, have been theoretically estimated and compared by previous studies to interpret observed variations in the geomagnetic field. However, the piezomagnetic field estimated in previous studies may not provide an accurate estimation because they ignored spatial variations in elasticity, leading to only a rough approximation of the properties of Earth's crust. In this paper, a semi-analytical procedure for calculating the piezomagnetic field arising from a point dislocation source embedded in a layered elastic medium is derived. Following a well-established method of the vector surface harmonic expansion, all of the governing equations written in partial differential equations in a real domain, together with the linear constitutive law of the piezomagnetic effect, are converted to a set of ordinary differential equations in a wavenumber domain. Equations in the wavenumber domain are solved analytically, and each component of the piezomagnetic field in the real domain is obtained after applying the Hankel transform. By using the derived procedure, the piezomagnetic and displacement fields due to a finite fault with strike-slip, dip-slip, and tensile-opening mechanisms are estimated for media with layered elasticity structures. Results for a finite fault are obtained by integrating the point source solution over the fault plane. The results of the numerical analysis allow the effect of heterogeneities in rigidity on the piezomagnetic effect to be examined and implications for the findings of previous investigations to be drawn. In cases where the moment-release at the dislocation source is fixed, the effect of the rigidity differences between upper and lower layers on the piezomagnetic field is minor even in the case where the Curie point depth is near the source of dislocation. This result is in contrast to a previous study that assumed the Mogi model and suggested that heterogeneities in the horizontal direction may be of importance when combined with layered rigidity structures. A contrast is seen between the piezomagnetic and displacement fields corresponding to models with layered rigidity structures: the piezomagnetic field is roughly proportional to the moment-release on a source fault, whereas the displacement field is proportional to slip or opening of the fault. Provided that the rigidity of the crust increases with increasing depth, the calculated piezomagnetic field is likely to have been underestimated in many earlier studies, which assumed uniform rigidity and a geodetically inverted size of slip.

Curie point depth analysis of aeromagnetic data of Kasane region in northwest Botswana and surrounding regions for geothermal investigation of Kasane Hot Spring

The Kasane Hot Spring with discharge temperatures of 43–50 °C is characterized by intermittent bubbling accompanied by white precipitant within its vicinity. The hot spring discharges mainly along Chobe River which meets the Zambezi River at the tip of northwest Botswana. In this study the Curie point depth (CPD) was estimated using the spectral centroid method of aeromagnetic data at Kasane Hot Spring and the surrounding regions. The upward continued aeromagnetic data were analyzed to obtain depths to the bottom (CPD) of the magnetic sources. The CPD values were then used to compute the geothermal gradient, subsurface crustal heat flow including radiogenic heat flow distribution in the region.According to the obtained results, the depth to the magnetic bottom varies from 6 to 22 km. These depths are comparable to those obtained from recent regional study of the Okavango Rift Zone. The areas with shallow CPDs of demagnetized rocks at depth are located around Kasane Hot Spring, where high heat flow values in the range 70–90 mW/m2 were recorded. Moreover, the radiogenic heat production values between 0.50 and 0.60 μWm-3 within the same region may also provide an extra contribution to the geothermal potential of Kasane Hot Spring. The correlation of estimated shallow CPDs with high geothermal gradient, high heat flows, and radiogenic heat flow values at area within Kasane region indicate possible geothermal resource. The CPDs values obtained may be associated with the seismic events in the region and surroundings. The mean earthquake depth of events that occurred within Kasane and surrounding areas from 1987 to 1991 is 10 km, while the mean Curie Point Depth is approximately 11 km. These seismic events in the area could be responsible for possible thermal accumulation at Kasane Hot Spring, resulting in high heat flow values in the area.

Crustal thickness, depth to the bottom of magnetic sources and thermal structure of the crust from Cameroon to Central African Republic: Preliminary results for a better understanding of the origin of the Bangui Magnetic Anomaly

The Bangui Magnetic Anomaly (BMA) is one of the largest magnetic anomalies in the world whose origin is still not known. This research investigated the crustal thickness, Curie depths and thermal structures in the Central African sub-regions – Cameroon, Central African Republic and adjacent countries – which are largely characterized by the Bangui Magnetic Anomaly. To achieve a better understanding and clearer idea of the location of the possible sources of the BMA, analyses of geothermal structures were conducted. Two potential methods were used: gravity to evaluate the crustal thickness and magnetics for geothermal analysis. Spectral analysis of gravity data shows that crustal thickness range between 14 and 55 km. The highest depths were found in Central African Republic. The lower values of crustal thickness were obtained in South-Chad basin with a minimum of roughly 14 km. Geothermal analysis is carried out using the Curie point depth, thermal gradient and heat-flow evaluations. The results show that the BMA is related to a thick crust of roughly 40 km. Depth to the bottom of possible sources does not exceed the lower crust. The mean Curie point depth estimated is 38 km with an error of ±2 km. Geothermal results also show the difference in the thermal behaviour between the crust in the Pan African and Precambrian domain. The mobile zone which constitutes the Pan African domain is associated with a thin crust of high heat-flow values of 65 mW/m2. However, the Precambrian domain beneath the BMA is associated with a thick crust with lower heat-flow values (roughly 45 mW/m2). The difference between crustal thickness and Curie point depths shows that all the sources of the BMA are crustal. The present results are in favour of a geological origin for the Bangui Magnetic anomaly.

What Controls Effective Elastic Thickness of the Lithosphere in the Pacific Ocean?

AbstractThe effective elastic thickness () of the lithosphere is a proxy for mechanical strength and can be used to constrain lithospheric rheology and understand how surface deformation relates to deep Earth processes. Here, we map variations over the Pacific Ocean from the inversion of the admittance between free‐air gravity anomaly and bathymetry data calculated using a continuous wavelet transform, taking both surface and subsurface loads into account. The Pacific lithosphere show ranging between 0 and 80 km with a mean of 13.5 km and a standard deviation of 12.3 km. We find that is generally poorly correlated with plate loading age, crustal age, heat flow and Curie point depth, except for relatively young (<60 Ma) and warm lithospheres. Most oceanic plateaus and seamounts show km, with the lowest values (<5 km) around active spreading centers. The highest estimates (>30 km) are found along subduction zones and around the Hawaiian‐Emperor Seamount Chain (HESC). Taken together, these results support a temperature control on for small loads and warm lithosphere through steady‐state creep processes, but strain hardening operating at large plastic strain and low temperature could explain high associated with large‐amplitude and long‐wavelength loads (subduction zones and the HESC) and should be incorporated in yield strength models of oceanic .

An approach for heat flow determination in the absence of geothermal gradient measurements: west Anatolia example

In western and southwestern Anatolia, the geothermal gradient cannot be accurately measured in many wells due to the complex horizontal water cycle. The aim of this study is to calculate the geothermal gradients by using a new approach for such wells. In this case, the first step is to calculate the geothermal gradients in order to estimate the heat flow values around the wells. Naturally, a direct heat flow estimate cannot be made for wells without a geothermal gradient. However, the heat flow values can be indirectly obtained by different methods. Curie point depth, silica geothermometer, and magnetotelluric conductive layer depth are some of these indirect methods. In this study, we used the heat flow data based on the Curie depth. In this approach, Curie temperature gradients are calculated using the Curie heat flow values and thermal conductivities for problematic wells. An empirical relationship between the Curie temperature gradient and the correctly measured temperature gradients in the region was established. With this relationship, it is possible to make an approach from the current Curie temperature gradient to the normal temperature gradient. In this way, heat flow can also be calculated for areas where no geothermal gradient can be obtained, and heat flow distribution over the whole area can be given. This proposed approximation, to obtain thermal gradient and heat flow, can also be extended to any other region.

Interpretation of aeromagnetic data for the geothermal properties in the northwestern part of Turkey

The northwestern part of Turkey is a significant area for its location on the accretionary region of several micro-continents and blocks. Therefore, there are several suture zones and western segments of the “North Anatolian Fault Zone” are scattered in the study area. Due to trans-tensional stresses, there are several pull-apart basins and/or depressions within the fault zone in the study area. As a consequence, it is also possible to observe magmatic intrusions into the fault segments. All these events and magmatic emplacements in the tectonic framework provide significant magnetic anomalies throughout the region.In this study, geothermal potential of the region is investigated based on the spectral analysis of the magnetic data, together with the seismic velocity (VP) distribution in the area using the log-linear relationship between the seismic velocity and the radiogenic heat production. Although two regions are emerging in the Curie Point Depth (CPD) and geothermal gradient maps, only one anomalous area from Bursa to Tekirdag may be considered as a promising region for the further geothermal energy exploration in the heat-flow maps prepared according to two different thermal conductivity coefficients. Seismic velocities are also low in this anomalous region decreasing down to 6.40 km/s around the shoreline of Tekirdag. Heat-flow values are increasing up to 110 mW/m2 in this particular area where the CPDs are around 14 km.

Estimates of Curie point depth, geothermal gradient and near-surface heat flow of Bida and environs, Nupe Basin, Nigeria, from high-resolution aeromagnetic data

The Nupe Basin is a northwest–southeast (NW–SE) trending intracratonic sedimentary basin in the central part of Nigeria with its coordinates defined by longitude 5°00′ to 8°00′ E and latitude 7° 00′ to 11° 00′ N. Spectral inversion of the high-resolution aeromagnetic data was carried out to estimate the Curie point depth (CPD), geothermal gradient and heat flow regime of parts of the Nupe Basin, Nigeria. The estimate of regional temperature distribution and the identification of thermally active regions within the study area were made from the spectral analysis of high-resolution aeromagnetic data which were divided into 16 overlapping spectral blocks to obtain the top and centroid depths of the magnetic sources which were later used to calculate the heat flow characteristics. The estimated Curie point depths range from 21.43–26.71 km with an average CPD value of 24.54 km, while the geothermal gradient ranges between 21.72 °C km−1 and 27.07 °C km−1 with an average value of 24.39 °C km−1. Similarly, the estimated heat flow regime of the study area ranges from 54.30 m Wm−2 to 67.67 m Wm−2 with an average value of 59.41 m Wm−2. The range of estimated geothermal parameters in the study area is an indication that the area is not a volcanic or thermally active region and therefore has little potentials for geothermal energy exploitation. The geothermal play of the area, therefore, was revealed to be of the conduction-dominated play type, typically a combination of the basement and intracratonic basin geothermal play types.

Geophysical constraints on the nature of lithosphere in central and eastern Tibetan plateau

The structure and rheology of lithosphere are fundamental to understanding lithospheric deformation operating within the Tibetan plateau and hence holds significant implications for continental dynamics. Yet, some of these aspects remain less well constrained in Tibet. In this study we construct new models of isotropic-average shear-wave velocity and radial anisotropy from previously published Rayleigh-wave and Love-wave phase velocities at periods of 8–143 s. Integrating with other previously published geophysical data, we demonstrate that a weak mid-to-lower crust is pervasive within the plateau, as directly inferred from seismically low velocity and high conductivity at these depths along with high Moho temperature. When combining with the observation of positive radial anisotropy patterns (Vsh > Vsv), we speculate that this weak mid-to-lower crust could probably flow towards southeastern Tibet, whereas in the Qinling Orogen this crustal flow is absent. This weak mid-to-lower crust in Tibet could decouple upper crust and lower crust/upper mantle, accommodating active deformation in response to the Indian-Asian convergence. Additionally, our results show that the subduction front of Indian lithospheric mantle (LM) could reach to the Bangong-Nujiang-Suture (BNS) in central Tibet and to the Jingsha-River-Suture (JRS) in eastern Tibet. We find no expected high velocity beneath northern Tibet to support southward subduction of the Asian LM. Instead, the northern Tibet is characterized with a continuous low-velocity-anomaly from Moho to 200 km. Coupled with the observations of shallow Curie-point depths and high Moho temperature, we infer that the Tibetan upper mantle in the north is hotter than that in the south, probably resulting from mantle upwelling due to either the Indian LM subduction, or thickened Tibetan lithosphere delamination with some contributions of shear heating and radioactive heating from the thickened Tibetan crust. This study highlights the nature of lithosphere, associated dynamic processes and the overall deformation within the Tibetan plateau.

Estimation of Curie point depth and geothermal gradient in parts of the Bida Basin, Nigeria

The purpose of this work is to estimate the Curie point depth, heat flow and geothermal gradient from spectral analysis of aeromagnetic data over the Bida and Baro areas, Bida Basin, north central Nigeria. The area covered is approximately 6050 km2 and bounded by latitudes 8° 30′ and 9° 30′ north and longitudes 6° 0′ and 6° 30′ east. The aeromagnetic maps were digitised at an equal interval, and the regional values were removed using polynomial fitting. The resulting residual data were subjected to the upward continuation technique to suppress the short-wavelength components of the residual magnetic anomalies. The upward continuation residual map was divided into eight overlapping blocks, and each block was spectrally analysed. The estimated Curie point depth ranges from 13.6 to 27.2 km, the geothermal gradient ranges from 21.3 to 42.6°C/km with an average value of 34.4°C/km and the corresponding heat flow ranges from 53.2 to 106.6 mW/m2. The average value of the geothermal gradient of 34.4°C/km indicates the possibility of hydrocarbon maturation in the area. Areas of geothermal anomalies with gradients greater than 40°C/km may be prospective for geothermal energy usage in Nigeria for generation of electricity.

Crustal and thermal structure of the Permian – Jurassic Luangwa – Lukusashi – Luano Rift, Zambia: Implications for strain localization in magma – Poor continental rifts

This work uses aeromagnetic, satellite gravity, and ground gravity data to image the thermal and crustal structures beneath the NE-trending Paleozoic - Mesozoic Luangwa – Lukusashi – Luano (LLL) rift in southeastern Zambia. This rift extends between the Precambrian Irumide metacraton in the northwest and the Niassa craton to the southeast and is partially controlled by the NE-trending Mwembeshi suture zone between the two blocks. Although the LLL rift is suggested to have been reactivated by the Southwestern Branch (SWB) of the East African Rift System (EARS), this work did not find shallowing of Curie Point Depth (estimated from the spectral analysis of aeromagnetic data) that would be indicative of elevated heat flow beneath the rift. Three-dimensional inversion of the aeromagnetic data shows a number of magnetized bodies, the largest occurring beneath the central part of the LLL rift and extending to a depth of ~35 km. Spectral analysis of the satellite gravity data indicates a ~45 km thick crust beneath the southwestern and central parts and the northeastern tip of the LLL rift. Two-dimensional (2D) forward modeling of the ground gravity data indicates a ~200 km wide and ~12 km thick under-plated mafic body (UPMB). These results support limited reactivation of the LLL rift by the SWB of the EARS. Further, extensional strain localization during the onset of the LLL rifting is attributed to the accretion of the UPMB beneath the crust.

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.

Evaluation of geothermal potential in some parts of Bida Basin of Nigeria using Curie point depths and heat flow from spectral analysis of aeromagnetic data.

The Centroid method of Spectral Depth analysis was used to evaluate the Curie point depth (CPD), Geothermal Gradient and Heat Flow in some parts of the Bida Basin of Nigeria with a view to determining the energy potential of the area. The reduced-to-pole aeromagnetic data was divided into 16 overlapping ensembles and Fast Fourier Transformed to decompose the anomalies into their energy and wavenumber components using Oasis montaj software. The radial power spectrum was calculated for each of the grid points with the locations of the centres of the ensembles and a plot of Energy spectrum versus frequency was carried out to generate two different gradients: s<sub>1</sub> and s<sub>2</sub> representing different depth source models. These gradients were used to evaluate the average depth to the top of the deepest crustal block, Z<sub>t</sub>, depth to the centroid of the deepest crustal block, Z<sub>0</sub>, CPD, Geothermal Gradient and Heat flow. From the results obtained, the CPD varied from 2.59 to 8.23 Km while the thermal gradient and heat flow in the area revealed values ranging from 70.45 to 224.15 <sup>o</sup>CKm<sup>-1</sup> and 176.13 to 560.37mWm<sup>-2 </sup>respectively. The results of the contouring in conjunction with the CPD, geothermal gradient and the heat flow values have shown that the area has a greater energy potential in the south-eastern block of Katonkarfi, with shallow CPD and high geothermal gradient and heat flow. These results could be incorporated in the GIS and available geological, geophysical and geochemical information of the area to facilitate selection of the optimum site for energy exploration.

MAGCPD: a MATLAB-based GUI to calculate the Curie point-depth involving the spectral analysis of aeromagnetic data

The Curie point-depth, frequently related to the depth to the bottom of the magnetic source, is widely employed as an estimator of temperature at depth when borehole temperature data are not available. The Curie point-depth is calculated using the spectral analysis of the magnetic data derived from aeromagnetic or satellite surveys. In this paper, MATLAB user-friendly GUI are constructed to calculate the Curie Point Depth using the inversion of aeromagnetic data assuming 2D fractal magnetization and modeling the temperature at depth assuming a 1D steady-state conductive heat transfer model. The program, tested in synthetic and aeromagnetic data, is running under MATLAB 2020a or standalone application with these input parameters: Aeromagnetic data, fractal parameter, Curie temperature, surface temperature, thermal conductivity, surface radiogenic heat production and scaling length of surface radiogenic heat production. The radially averaged amplitude spectrum, scaled spectrum, modeled spectrum, Curie point-depth, and temperature profile at depth are the output parameters of the program. Finally, the program is tested with Texas aeromagnetic data, and the results of the Curie point-depth were compared with borehole data.

Correlations between oceanic crustal thickness, melt volume, and spreading rate from global gravity observation

Oceanic crustal accretion at mid-ocean ridges is a function of spreading rate, mantle temperature, and composition, which are intertwined in affecting melt production and oceanic crustal thickness. Sparse and irregular seismic and geochemical observations on a global scale showed no correlation between crustal thickness and spreading rate along slow to fast-spreading centers. Here, we compile a global oceanic crustal thickness model from gravity data to revisit this issue at a high resolution. Gravity-observed melt volume shows a positive correlation with spreading rate globally, implying that spreading rate is the dominant factor in melt production. However, oceanic crustal thickness is negatively correlated with spreading rate from slow to fast-spreading centers, and this trend is further consolidated by the increase in Curie point depth (a geothermal proxy) and ridge depth with increasing spreading rate. Thus, a decreasing near-ridge temperature probably contributes to crustal thinning from slow to fast-spreading centers. Inferred low melt volume anomalies beneath fast-spreading centers are consistent with a 20 °C temperature drop in the near-ridge mantle, likely caused by efficient hydrothermal cooling.

Hydrogeochemical characteristics of the thermal and non-thermal waters in the western side of the Sultandağ Massif, SW Turkey

Thermal, non-thermal, and mineral waters of different hydrogeochemical properties can be found along the same tectonic region on the western side of the Sultandag Massif in Southwestern Turkey. A total of eight representative water samples were taken from the thermal, non-thermal, and mineral waters in the study area. The waters in the study area are divided into 3 different facies: (i) Ca-Mg-HCO3, (ii) Ca-Mg-HCO3-SO4, and (iii) Ca-Mg-SO4-(HCO3). Major hydrogeochemical processes that control the chemical composition of waters in the region are carbonate and silicate weathering. Thermal and mineral waters in the region have high dissolved ion content due to intense water-rock interaction. The surface temperatures of geothermal waters were found to be between 22.1 and 33.9 °C, and reservoir temperatures, which ranged between 30 and 84 °C, were calculated according to geothermometer evaluation. The heat source of the thermal waters in the study area is thought to be related to the geothermal gradient. Using the Curie point depth (DCPD: 17 km) and Curie point depth temperature (TCPD: 580 °C) data, the geothermal gradient and heat flow in the region were determined to be 34.12 °C/km and 71.65 mW/m2, respectively. Based on these data, it is determined that the waters come from a depth of 1.50–2.47 km.

Review of Curie point depth determination through different spectral methods applied to magnetic data

SUMMARYSpectral methods have been applied for more than 40 yr to calculate the depth to magnetic sources and the Curie point depth or Moho depth. Unfortunately, conceptual, theoretical and methodological errors, as well as, subjective approaches and lack of rigor in the application of the method are common. This has affected reproducibility, credibility and confidence in this method.We carried out a detailed mathematical and methodological revision of the spectral methods (centroid, spectral peak, forward and fractal methods) applied to magnetic data for the determination of the depth to magnetic sources. Moreover, a systematic analysis of more than 110 articles was done in order to compile and compare the different approaches and values of key parameters used by different authors in their calculations. We discuss difficulties, conditions and methodological procedures, as well as several misapplications and misinterpretation of the different methods.

Comparison among the natural radioactivity levels, the radiogenic heat production, and the land surface temperature in arid environments: A case study of the El Gilf El Kiber area, Egypt

The El Gilf El Kiber area is one of the most promising areas for urban growth and reclamation projects in the southwest of Egypt. In the study area, the lithological units vary in age from Precambrian (mainly granite) to Quaternary (mainly sand sediments). The analysis of airborne magnetic and gamma-ray spectrometry data was incorporated into that of the remote sensing data (Landsat-8). The integrated analysis was used to detect the lithological distributions and to delineate the subsurface basement rocks that control the radioactivity in the study area. It was also used to determine the relationship between radiogenic heat production (RHP) and land surface temperature (LST) that was retrieved from the Landsat-8 thermal infrared sensor (TIRS) data. The output of the principal component analysis (PCA) of Landsat-8 Operational Land Imager (OLI) data is a false-color map (PC1, PC2, and PC3 as red, green, and blue, respectively) displaying the various lithological units in the study area. The LST map, calculated from Landsat-8 TIRS data, shows that the surface temperatures range from approximately 41 to 53 °C. The highest concentrations of eU, eTh, and K in the area were 25 ppm, 121 ppm, and 7.8%, respectively. The RHP values ranged from 1.1 μW/m3 to 15.1 μW/m3. These relatively high anomalies are associated with basement outcrops and the sedimentary rocks overlying shallow basement rocks. The total horizontal derivative (THD) of the magnetic data delineates the horizontal extension of the basement rocks. The Curie point depth (CPD), estimated from magnetic data, ranges from 35.5 km to 41.0 km. The results also exhibited geothermal gradients ranging from 16.10 °C/km to 14.14 °C/km, and heat flow ranges from 35.4 mW/m2 to 40.8 mW/m2. It was evident after comparing that the RHP and LST maps exhibited the same features as the gamma-ray spectrometric maps. Moreover, the areas around the basement rocks exhibited higher radioactivity, RHP, and temperature than the basement rocks themselves.

INVESTIGATION OF GEOTHERMAL ENERGY POTENTIAL OF PARTS OF CENTRAL AND NORTH-EASTERN NIGERIA USING SPECTRAL ANALYSIS TECHNIQUE

The current study deals with an estimate of the Curie point depth, heat flow and geothermal gradient from spectral analysis of aeromagnetic data covering an area located approximately between latitude 7.5o N to 11.5o N and longitude 7.5o E to 10.5o E, which corresponds to parts of the Benue trough (lower part of the Upper Benue trough, the entire middle Benue trough, and upper part of the Lower Benue trough), lower part of the Gongola and Yola Basins, the Precambrian Basement, the Jurassic Younger Granites and two prominent hot Springs, Wiki hot spring in Bauchi state (in the north-eastern part) and Akiri hot spring in Nasarawa state (in the south-western part) of central and north-eastern Nigeria. Radially power spectrum was applied to the aeromagnetic data of the study area divided into 48 square blocks and each block analysed using the spectral centroid method to obtain depth to the top, centroid and bottom of magnetic sources. The depth values were subsequently used to evaluate the Curie-point depth (CPD), geothermal gradient and near-surface heat flow in the study area. The values of the curie point depths (Zb), range from 7.6341 km to 34.5158 km, with a mean value of 14.7928km, geothermal gradient, range from 16.8039 0C km-1 to 75.97490C km-1, with mean value of 45.7021 0C km-1 and heat flow (q), range from 42.0097 mWm-2 to 189.9372mWm-2, with a mean value of 114.2554mWm-2. Which reveals that, there might probably be good sources for geothermal and thereby further recommended for detailed geothermal exploration.

Study of Curie point depth and heat flow from spectral analysis of aeromagnetic data for geothermal potential of Gubio, Chad Basin, Nigeria

Aeromagnetic data of Gubio area, Chad Basin, northeastern Nigeria, were interpreted quantitatively by employing spectral analysis technique with the aim to estimate the Curie point depth, geothermal gradient and heat flow in order to determine the geothermal nature of the area. Data enhancement (reduction to pole, RTP and band pass filter) was performed on the total magnetic intensity (TMI) map of the area using oasis Montaj software. The enhanced map was divided into four overlapping blocks, and each block was subjected to spectral analysis. The results gave Curie point depth values ranging from 10.63 to 20.07 km, with deepest depth at the northeast, while the shallowest depth was observed to be conspicuous in the southeastern part of the study area. The estimated geothermal gradient ranges from 28.90 to 54.57 °C km−1 with an average value of 40.26 °C km−1, with low values in the northeast direction, and increases towards southeast. The average geothermal gradient of 40.26 °C km−1 indicates the possibility of hydrocarbon generation and accumulation in Chad basin. The estimated heat flow values range from 72.24 to 136.43 mW m−2 with an average value of 100.65 mW m−2, the highest values are found around southeastern part of the study area, and the lowest values are within the northeastern part. The areas of geothermal anomalies with gradient above 50 °C km−1 may be good areas for geothermal reservoir exploration for an alternative source for power generation.

Curie point depth and heat flow deduced from spectral analysis of magnetic data over Adamawa volcanic region (Northern Cameroon): geothermal implications

This study presents an estimation of Curie point depth (CPD), heat flow and geothermal gradient from spectral analysis over the Adamawa volcanic region (northern Cameroon). The spectral analysis method is applied to the reduced-to-equator (RTE) magnetic anomaly data of the region. Grid Earth Magnetic Anomaly (EMAG2) data were divided into 17 zones. RTE magnetic anomaly data were low-pass filtered to remove the effects of topography. Then, the data were transformed into the Fourier domain in order to determine the spectrum of the magnetic anomaly data for the study region. Then, the depth values are used to estimate the CPD, the geothermal gradient (GG) and the heat flow in the Adamawa region of Cameroon (Central Africa). The acquired results indicate that the CPD varies between 15.97 and 41.16 km with an average of 27.52 km. GG varies between 14.09 and 36.31 °C km−1 with an average of 22.27 °C km−1 and the resulting heat flow varies between 35.23 and 90.78 mW m−2 with an average of 55.68 mW m−2. The variation in heat flow and GG shows an abnormal geothermal condition of the area. It is found that there is a geothermal potential precisely at Woulnde in the Adamawa region. The obtained results can serve as a guide for government and private partners to explore this energy source.