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Western Saudi Arabia is a promising area for geothermal energy exploration. Its geothermal wealth is attributed to the ongoing Red Sea rift evolution and crust thinning. Several hot springs in the region indicate the presence of potential geothermal resources. The present study aimed to characterize the geothermal system of a hot spring in the region, in the area of Wadi Al Lith, where water temperature exceeds 80 °C at the surface. For this, we used aeromagnetic data from the Saudi Geological Survey. We also collected a ground magnetic gradient data profile near the hot spring. To delineate structures of interest and map the distribution of volcanic rocks and tectonic lineaments, data enhancement filters were applied to the aeromagnetic data. These data were also subjected to spectral analysis to determine the depth of the Curie isotherm, which was then used to estimate a 1D geothermal model and predict the heat flow in the study area. According to the results of the spectral analysis of aeromagnetic data, the depth of the Curie temperature isotherm was about 14.8 km. The estimated depth was validated by deep magnetotelluric soundings, which revealed a clear decrease in resistivity at the same depth level. A constrained 1D geothermal model with three different layers (upper crust, lower crust, and mantle) was constructed. The depth of the Curie isotherm and the depth to the lithosphere's base were among the constraints. Furthermore, published data were used to define the radiogenic heat production within the crust and mantle and the corresponding thermal conductivity and thickness of each layer. According to the 1D geothermal modeling results, the average heat flow of the area reaches 109.8 mW/m2, indicating potential geothermal resources. The findings of this study can be used to design a drilling program that will provide detailed information on reservoir parameters and put the geothermal resources into production. [ABSTRACT FROM AUTHOR]

The Bida and Anambra Basins are major inland sedimentary basins located in the central and southern part of Nigeria with possible hydrocarbon potential but lack exploratory data. The present study aims at providing base line information on the thermal regime of the sedimentary basins, which would significantly contribute to its hydrocarbon prospect, investment opportunity and exploitation. The spectral analysis of the aeromagnetic anomaly data from the southern Bida Basin, northern Anambra Basin and adjacent basement complex terrain reveals the Curie point depth (CPD), geothermal gradient and heat flow in the region. The data reveals a CPD that varies between 19 and 30 km while the geothermal gradient is from 23 to more than 44 °C/km with heat flow values ranging from 50 to 109 mW/m2 in the southern Bida Basin. In the northern Anambra Basin, the CPD values range from 6.8 to 20 km and the heat flow values vary between 59 mWm2 and 109 mWm2, with a localized shallow CPD value of less than 6.8 km and associated high heat flow of 109 mWm2 in the central part of the basin. The delineated thermal patterns in the Bida and Anambra Basins are interpreted to be associated with the intrusions and the presence of deep-seated rift. The interpretation of the aeromagnetic data shows good agreement with the land surface temperature obtained from remote sensing data of the study area. The distribution of heat patterns in the southern Bida and northern Anambra Basins have implications for geothermal, source rock maturation and hydrocarbon generation evaluation of the basins. [ABSTRACT FROM AUTHOR]

With the deteriorating electrical power supply in Nigeria, it is imperative that more alternative sources are explored. This research work is carried out to assess part of the Bida basin as a possible source of geothermal energy that will help to augment the electric power generation in the country. The study was carried out within the northern sector of the Bida Basin and environs and the area which lies between Longitudes 5000'00" - 7000'00" E and Latitudes 8030'00" - 10030'00" N. Sixteen (16) half degree high resolution aeromagnetic data in a block grid format was utilised for this research. To enhance data for interpretation the total magnetic intensity (TMI) map was subjected to regional-residual separation using Oasis Montaj (version 7.0.1) software. To minimize the effect of frequency noise caused by tiny structures near ground surface, the residual magnetic map was upward continued and further divided into sixteen square blocks with each block windowed and subjected to spectral analysis using Matlab (version R2010a) software. Surfer 11 surface mapping software was used for data contouring. Results obtained from the analysis revealed a Curie point depths ranges from 9 - 17 km over the study area, a geothermal gradient range from 32 - 65 ℃ km-1, and heat flow ranges from 83 - 163 m Wm-2. From interpretation of heat flow map, the prospective areas with anomalous geothermal conditions recommended for geothermal exploitation are areas around Masamagu, Mokwa, Bokani, Lapai, Agaie and Agena. [ABSTRACT FROM AUTHOR]

Geothermal energy potential investigation over parts of Middle Benue Trough, Nigeria, has been evaluated using aeromagnetic and aeroradiometric datasets. The input data consists of nine aeromagnetic and aeroradiometric sheets, respectively. The aeromagnetic data was assembled and digitized; this produces a total magnetic intensity anomalous map (TMI). Similarly, the radiometric data were contoured to produce maps for the three radiometric elements of K, Th, and U. The rose diagram showed that the structural trend in the study area is trending NE-SW and the minor ones are trending E-W and NNE-SSW directions. The radiometric heat model reveals areas of high and low geothermal gradient. The results of quantitative interpretation reveal that the depth to anomalous magnetic sources (the sedimentary infilling) ranges between 0.76 and 4.46 km; while the depth to centroid ranges between 7.29-19.6 km. The Curie point depth (CPD) corresponds to the depth to the bottom of the anomalous magnetic source. The CPD varies from 12.70-37.22 km, the geothermal gradient varies between 15.58-45.670C/km, and the geothermal heat flow varies from 38.9-114.17 mW/m2. The two dimensional structural models show uplifted crust and mantle in some areas due to magmatic intrusions, which gave rise to low CPDs (12 to 28 km), which resulted in high geothermal heat flow values (60 to 115 mW/m2). The geothermal heat flow values around Kwolla, Shendam, Lafia, Akiri, Ibi, and Wukari South fall between 60 and 100 mW/m2, which is the suitable standard for geothermal potentiality. [ABSTRACT FROM AUTHOR]

Rheology of solids is primarily a function of temperature. Mapping depth to the bottom of the magnetic layer (DBML), which is assumed as a proxy for the depth to Curie temperature, can be used to constrain the thermal structure of the lithosphere. Heat flow data are commonly used to address the thermal structure of the lithosphere. However, these data are scarce for the Amazon Craton. Therefore, as an alternative, DBML was calculated using fractal magnetic source distribution. The Amazon craton is usually described in terms of geochronological provinces models. Nevertheless, geophysical data are poorly discussed in these models. We provide a DBML model that was integrated with the potential field, seismic tomography, and crustal thickness data to address this issue. Our model varies from 10 to 80 km, and almost 90% of the estimates are in the 20‐50 km range. The recurrence of long‐wavelength features on independent datasets supports the assessment that the model is robust and recovered real geophysical signals. Our model suggests that the limits between Carajás and Bacajás domains should be revisited as well as the limits between Tapajós and Iriri Xingú domains. Moreover, we also correlate the model with main mineral deposits. Further, the identified DBML anomaly suggests the mantle is serpentinized in the eastern Carajás domain. This feature is highly correlated with high p‐wave velocity indicating fertile mantle conditions, thus making this region favorable for world‐class mineral deposits. Plain Language Summary: Ferromagnetic materials demagnetize when they reach the Curie temperature. On Earth, temperature and depth increases are directly proportional so that the Curie point is achieved at a certain depth. We used a specialized code to calculate Curie points/temperature for the Amazon Craton to understand the meaning of hot and colder areas. Cratons are geological bodies located distant from current tectonic activity while also showing evidence of the evolution of the past configurations of the continents. Understanding the relationship between the domains may elucidate the past configurations of the cratons and how they evolved. We compared our estimates with the depth of Mohorovic discontinuity, which is a boundary between crust and mantle and usually around 40 km for cratonic areas. We noticed that deposits of ferrous and metals base occur preferentially where the mantle is magnetic. Key Points: We used the depth to the bottom of the magnetic layer to predict the thermal structureOur model suggests changes to the limits of Carajás and Bacajás domains as well as the Tapajós and Iriri Xingu domainsSerpentinized mantle portions correlate with world‐class mineral deposits in the Carajás domain [ABSTRACT FROM AUTHOR]

The East Anatolian Fault Zone (EAFZ) with an average length of 500 km is one of the most seismically active regions of Turkey, and many major earthquakes have occurred along this fault zone. The earthquake of 24 January 2020 (Mw = 6.8) with the epicenter in Sivrice (Elazığ) occurred on the EAFZ and caused loss of life and property. This study was carried out to investigate the Coulomb stress changes before and after the Sivrice mainshock by using 89 earthquakes (M ≥ 4.5) with different depth ranges (7.5, 15, 22.5, 30 km) that occurred in the EAFZ between 1997 and 2020. Coulomb stress change maps were created using the Sivrice (Elazığ) mainshock and subsequent earthquakes. The maps showed that the stress continued in the northeast and southwest directions and caused a positive Coulomb stress change. According to the Conrad discontinuity depth calculation obtained from the thermal investigation covering the EAFZ and its immediate surroundings, a value of 21.2 km was obtained. While there was no stress increase at depths deeper than 20 km before the Sivrice mainshock, there was a stress increase up to 30 km after the mainshock. Rigidity of crustal structure is higher between segments 1 and 5 compared to segment 6 according to results of Curie Point Depth (CPD) on the EAFZ. This induced the positive Coulomb stress change along with the fault segments at the deeper depth levels. The high Coulomb stress values were especially observed around the Palu-Hazar Lake and Çelikhan-Gölbaşı segments. Therefore, these segments were defined as the earthquake hazard potential region. [ABSTRACT FROM AUTHOR]

This study attempt to estimate the Curie point depth (CPD) and heat flow using high resolution aeromagnetic data over part of Bida basin bounded with longitude 5o00’E – 6o30’E and Latitude 8o30’N – 9o30’N with an estimated total area of 18,150 km2. We subjected the total magnetic intensity field of the study area to regional/residual separation using polynomial fitting. We divided the residual map into sixteen overlapping spectral blocks. We obtained centroid depths (Zo) and depth to top of basement (Zt)got from the plot of log of power spectrum against wave number; the centroid depth ranges from 6.61 km to 20.30 km while the depth to top of basement ranges from 1.59 km to 6.38 km. input parameter to calculate the curie depth (Zo). The CPD range from 10.88 km to 35.51 km with an average value of 23.22km. The CPD is deeper at the centre of the southern and eastern part of the study area which correspond to part of Pategi and part of Baro; and shallow at the northeastern and Northwestern part of the study area correspond to part of Mokwa and part of Bida. The geothermal gradients for the sixteen blocks range from 16.33 oCkm-1 at the centre of the southern region of the area to 53.30 oCkm-1 at the northeastern and north western region of the study area with an average of 28.98 oCkm-1. While the heat flow to range from 40.99 mWm-1 to 133.80 mWm-1 with an average value of 76.19 mWm-2. It can therefore be deduced from this study that the Southeastern, southwestern, and the northwestern part of the study area might be a good indicator of geothermal energy potential with minimum CPD, maximum geothermal gradient and heat flow since demagnetized rocks confirm a hot rock quantity in the crust that can be harnessed for geothermal energy exploitation.

Of the world's oceans, the Pacific has the most abundant distribution of seamount trails, oceanic plateaus and hot spots, and has the longest fracture zones. However, little is known of their thermal structures due to difficulties of heat flow measurement and interpretation, and in inferring thermal anomalies from low-resolution seismic velocities. Using recently published global magnetic models, we present the first independent constraint on Pacific geothermal state and mantle dynamics, by applying a fractal magnetization inversion model to magnetic anomaly data. Warm thermal anomalies are inferred for all known active hot spots, most seamount trails, some major fracture zones, and oceanic lithosphere between ~100 and ~140 Ma in age. While most Curie points are among the shallowest in the zone roughly bounded by the 20 Ma isochrons, abnormally deep Curie points are found along nearly all ridge crests in the Pacific, related to patchy, long-wavelength and large-amplitude magnetic anomalies that are most likely caused by prevailing magmatic or hydrothermal processes. Many large contrasts in the thermal evolution between the Pacific and North Atlantic support much stronger hydrothermal circulation occurring in Pacific lithospheres younger than ~60 Ma, which may have disguised from surface heat flow any deep thermal signatures of volcanic structures. Yet, at depths of the Curie points, our model argues for warmer Pacific lithosphere for crustal ages older than ~15 Ma, given a slightly higher spatial correlation of magnetization in the Pacific than in the North Atlantic.

To quantitatively understand the geodynamic process of a region, study of geothermal parameters underneath the earth surface is very paramount. Curie depth can be an alternative to delineate geothermal parameters. In the present study, we estimated Curie depths from the power spectra of 25 equally window sizes areas/points with 50% overlap extracted from high-resolution aeromagnetic anomalies of parts of lower and middle Benue Trough, Nigeria using modified centroid method based on fractal distribution of magnetic sources. Curie depths with associated uncertainties calculated from the region under study are between 11 ± 2 and 27 ± 2 km. The shallowest depth (11 ± 2) km is calculated around the area of Abakaliki whereas the deepest depth is calculated around Otukpa area of Anambra basin. The shallowest Curie depth as calculated is related with the Abakaliki anticlinorium while the deepest result is in connection with the Anambra basin. These suggest that different geological structures and magnetic anomalies (i.e. high or low magnetic anomaly) influenced the calculated Curie depth results. In the region, it is noted that lower Curie depths (14–18 km) are recorded over the basement rocks and Curie depths between 18 and 22 km within zones of volcanoes. The interpretation hypothesized presence of underplating in the crust and possibly mantle plume as a result of the Mesozoic–Cenozoic volcanic magmatism (magmatic centers) mostly basalts distributed and scattered in the region. It has also been hypothesized that the uncertainties calculated (± 0.2 to ± 5.0) in the region correlate more strongly with the geology, tectonic structures and type of anomalies than estimated Curie depths. [ABSTRACT FROM AUTHOR]

The Gulf of Cadiz has been affected by a long and complex geodynamic evolution. The lithospheric structure is poorly understood in this region, and it also shows a diffuse seismicity, spanning over a broad area. The Canary Archipelago has been extensively studied. Nevertheless, there are fundamental topics that are still under debate. No studies have addressed or suggested the possibility of a plausible geodynamic connection between both remarkable locations. In this study we integrate total tectonic subsidence (TTS), Curie point depth (CPD), Bouguer gravity anomaly, and seismic information. TTS shows the existence of a basement bulge in the area of the Canary Archipelago that extends to the north, and in the area of Madeira Island, which extends in a more subtle way to the north, too. Likewise, the CPD reaches the shallowest values in the same location at the Canary Archipelago. These two aspects suggest a cause-effect relationship between TTS and CPD at this specific area. Gravity data and CPD show a linear feature, which links the NW of the Canary Archipelago and the Gulf of Cadiz. The data we manage in this work show remarkable clues as: (a) the absence of a similar signal in the TTS, (b) the fact that CPD it is rather constant along this track, (c) CPD amplitude also almost doubles the values obtained on Canary Archipelago, and (d) the existence of a clear correlation between seismogenic depths and CPD, which points to the existence of a correlation between seismicity and the thermal architecture of the lithosphere. All of these evidences support the presence of a lithospheric thinning between Canary Islands and Gulf of Cádiz area, and in turn, the presence of an asthenospheric channel which feeds and alter locally the Eurasia–Africa Plate Boundary. [ABSTRACT FROM AUTHOR]

Antarctic geothermal heat flux is a basic input variable for ice sheet dynamics simulation. It greatly affects the temperature and mechanical properties at the bottom of the ice sheet, influencing sliding, melting, and internal deformation. Due to the fact that the Antarctica is covered by a thick ice sheet, direct measurements of heat flux are very limited. This study was carried out to estimate the regional heat flux in the Antarctic continent through geophysical inversion. Princess Elizabeth Land, East Antarctica is one of the areas in which we have a weak understanding of geothermal heat flux. Through the latest airborne geomagnetic data, we inverted the Curie depth, obtaining the heat flux of bedrock based on the one-dimensional steady-state heat conduction equation. The results indicated that the Curie depth of the Princess Elizabeth Land is shallower than previously estimated, and the heat flux is consequently higher. Thus, the contribution of subglacial heat flux to the melting at the bottom of the ice sheet is likely greater than previously expected in this region. It further provides research clues for the formation of the developed subglacial water system in Princess Elizabeth Land.

The sinking of the ocean sea bottom is produced by thermal cooling of the lithosphere. This evolution is determined by the underlying asthenospheric mantle. Estimation of the Curie Depth variations in the Scotia Sea by using a spectral approach and applied on magnetic anomaly data led us to determine a thermal model and derive a heat flux map. Using multichannel seismic and bathymetry data, we show that the West Scotia Sea reaches thermal equilibrium more quickly than other oceans do and thermally behaves like old oceanic crust in large oceans, following a different empirical age (t, in Ma)‐depth (d, in m) relationship, d(t) = 4,480 − 19,380 exp(−t/4). For oceanic crusts of the same age, underlain by different shallow mantle controlling the heat supply, low heat flux values imply older ages than those predicted for large oceans based on the empirical relationships of the standard plate model. These circumstances, together with the new heat flux map, shed light on the anomalous evolution of the Scotia Sea, a consequence of the present Pacific mantle outflow through the Drake Passage. Two branches of elevated heat flux surround the Shackleton Fracture Zone and extend to the northern and southern boundaries of the Scotia Plate. Most of the heat sources are located in the flanks, whereas the colder parts are centrally located. This signature supports the Drake Passage's role as a main mantle gateway for Pacific outflow toward the Atlantic reservoir favoring the oceanic spreading activity of this ocean. Key Points: The thermal evolution of the Scotia Sea is anomalous compared with other oceansThe heat flux pattern reveals asthenospheric branches close to the Scotia Sea boundariesScotia Sea and Drake Passage represent a main gateway for Pacific mantle outflow [ABSTRACT FROM AUTHOR]

As an independent geothermal proxy, the Curie-point depth has important geodynamic implications, but its estimation from magnetic anomalies requires an understanding of the spatial correlation of source magnetization, mathematically characterized by a fractal exponent. In this paper, we show that fractal exponent and Curie depth are so strongly inter-connected that attempts to simultaneous or iterative estimation of both of them often turn out to be futile. In cases of true large Curie depths, the iterative "de-fractal" method has a tendency of overcorrecting fractal exponents and thereby producing erroneously small Curie depths and smearing out true geological trends. While true fractal exponent can no way be constant over a large area, a regionally fixed fractal exponent is better than any mathematical treatments that are beyond the limit of data resolution and the underlying physics. [ABSTRACT FROM AUTHOR]

In western Canada, geophysical studies infer an abrupt change in crustal temperatures between the Canadian Cordillera and the adjacent North American craton, with important implications for the tectonics and geodynamics of the area. We use a wavelet analysis of magnetic anomaly data in western Canada to map the depth to the bottom of the magnetic source, or Curie depth. This depth corresponds to the point at which crustal rocks reach their Curie temperature, thus providing an estimate of geothermal gradient. Our model is defined by a fractal distribution of magnetization characterized by the parameter β, as well as the depths to the top (zt) and bottom (zb) of the magnetized layer. Synthetic tests reveal the increased accuracy of the estimated zb when values for zt and β are fixed prior to the inversion. We set zt to the thickness of sedimentary rocks overlying the magnetic bedrock and use various values of β to estimate zb. We determine β a posteriori by comparing Monte Carlo simulations of predicted heat flow values (assuming a Curie temperature of 580 °C) with observed heat flow in various regions. Our results suggest a β value of 2.5 for the Canadian Cordillera and Slave craton, and 2 for the remaining North American craton. The Curie depths resolve geological domains and important structural features, with estimates for zb averaging 15 ± 1 km in the Cordillera, 32 ± 3 km in the Slave craton, and 34 ± 3 km in the North American craton to the south. Plain Language Summary: Despite a relatively high elevation, geophysical imaging of the Earth beneath Canada's western mountains reveals a distinct 150 km thinning of the tectonic plates. The plates define the rigid outer shell of the Earth, and the thickness change is coincident with a topographic difference (higher) at the surface and a temperature difference (hotter) at depth. The relationship between the high topography with the thinner tectonic plate and hotter material at depth is not well understood. The objective of this research is to estimate temperatures of the Earth's crust below the surface in western Canada using the magnetic properties of rocks. At a certain temperature, rocks lose their magnetization and therefore do not produce magnetic anomalies. By analyzing magnetic anomaly data, we can infer the depth at which this temperature is achieved, which provides estimates of the thermal gradient in the crust. Combining these estimates with heat flow measurements provides more accurate constraints on the physical properties of the tectonic plate and will allow different tectonic models to be evaluated, allowing for a better understanding of the mechanical behavior of the Canadian Cordillera. Key Points: The wavelet transform is used to map the depth to the bottom of the magnetized source in western CanadaWe use a fractal distribution of crustal magnetization, which is seen to vary within the study areaCurie depth estimates are 15 ± 1 km in the Cordillera, 32 ± 3 km in the Slave craton, and 34 ± 3 km in the North American craton [ABSTRACT FROM AUTHOR]

• The northward extension of Godavari graben towards NSL revealed from both gravity and inverted Moho maps. • Heat flow map obtained from Curie depths shows higher heat flow below NSL and Godavari graben. • A complex high-density crust below NSL reveals imprint of multiple reworking along mobile belt/ fold belt. • The shallower DBMS compared DSS Moho depths below NSL reveals it as a thermal boundary. Narmada-Son Lineament (NSL) is a prominent geo-tectonic feature located in central India, characterised by complex geological structures and evolutionary history. In this study, we present a detailed joint interpretation of the aeromagnetic and gravity anomaly maps to delineate the crustal structure in order to address the thermo-tectonic activity below the NSL region. The ENE-WSW linear trend observed in the aeromagnetic anomaly map correlates well with the major tectonic elements of the NSL and the Vindhyan basin. The low-pass filtered regional gravity anomaly map and corresponding residual anomaly map revealed several crustal-scale structural features in the study area. The Curie depth map of the region prepared from the magnetic anomaly map shows the variation in depth between 24 and 48 km. The corresponding heat flow map correlates well with the trends in surface heat flow data. The gravity-derived Moho depth map reveals that the values vary between 30 and 59 km in the NSL region with deeper Moho below the Vindhyan basin. Further, the crustal models obtained from the constrained potential field modelling for two long transects across the NSL in the present study area revealed i) the absence of crustal underplating in the eastern part of NSL below Hirapur-Mandla region, ii) the presence of mid-crustal horst like structure below NSL, iii) undulating Moho with higher density crustal rocks within the NSL compared to the surrounding areas. The modelled crustal structure and the analysis of Curie depth as well as heat flow maps of the study area, reveal that the NSL region was affected by repeated tectonic activities since the Proterozoic times, and the present-day tectonics of this belt is greatly influenced by the reactivation of pre-existing faults along the NSL. [ABSTRACT FROM AUTHOR]

Abstract A prominent positive gravimetric and magnetic anomaly stands out in the region of the Guadalquivir-Portimão Banks, Gulf of Cadiz, off SW Iberia. The bathymetric and gravimetric highs have been interpreted as resulting from basement uplift occurred during Mesozoic rifting followed by overthrusting during the Alpine orogeny. However, we show that basement uplift alone does not account for the observed magnetic anomaly, implying that an additional magnetic source must be considered for an integrated model that fits with all the data. We present a new magnetic study that calls for the existence of a large magmatic body intruded beneath the Guadalquivir and Portimão Banks, the Guadalquivir-Portimão intrusion. We perform 3D inversion of magnetic data to obtain a susceptibility model that estimates the shape and extension of the intrusion. The modeled volume is constrained by estimation of regional Curie depth and the susceptibility model is limited to a realistic range, allowing interpretation in terms of rock nature. To clarify the relationship between the intrusion and the local lithospheric structure, we build 2D cross-sections integrating the modeled intrusion with recent crustal models and use 2D forward modeling to ensure that both the predicted magnetic and gravimetric fields fit the observed data. These sections show the Guadalquivir-Portimão intrusion emplaced along a lithospheric decollement within the necking domain of the Algarve rifted margin, across the lower and upper crust. It is suggested that is crosscuts Jurassic sedimentary sequences, suggesting that it intruded after continental rifting. Given the similarities with other onshore magnetic anomalies corresponding to Late Cretaceous alkaline intrusions, it is likely that the Guadalquivir-Portimão intrusion represents the southernmost expression of the Late Cretaceous alkaline magmatic event that affected both onshore and offshore West Iberia, becoming the fourth element of the enigmatic NNW-SSE trending alignment of Sintra-Sines-Monchique plutons, whose significance remains to be fully understood. Graphical abstract Unlabelled Image Highlights • The Guadalquivir-Portimão magnetic anomaly is not explained by basement uplift • 3D magnetic inversion calls for a ~80 × 20 × 10 km magmatic intrusion • The intrusion is along the necking domain of South Iberia rifted Tethyan margin • Intrusion emplaced into lithospheric detachment of Ocean Continent Transition • 300 km long N28°W alignment of four Cretaceous alkaline complexes in West Iberia [ABSTRACT FROM AUTHOR]

In the quest for alternative or renewable energy resource, attention is being focused on geothermal energy within some parts of the Niger Delta Basin of Nigeria with the aim of exploring/identifying its geothermal potentials. A MATLAB program was used to perform regional-residual separation and spectral analysis on composite-eight (8) aeromagnetic maps. Specifically, statistical spectral analysis was used to determine Curie point depth and heat flow values within this area. Results showed that the centroid depth varies between 14.4194 km (within Okigwe – Aba sector) and the 6.7482 km (within Aba-Ahoada region) while the depth to Curie temperature isotherm varies between 7.4644 km and 24.8600 km below the mean sea level. It was also found that the Curie temperature isotherm within the basin is not a horizontal level surface but an undulating surface with geothermal gradients and heat flow ranging between 12.0676 and 40.1910 °C/Km and 25.3419 and 84.4010 mW/m 2 respectively. Thus the calculated average geothermal gradient and heat flow for this area are 22.4886 °C/Km and 52.6012 mW/m 2 respectively. Since the value obtained from this work is below 100 mW/m 2 which is the minimum standard, it then means that this area may not potential be viable as a geothermal source. [ABSTRACT FROM AUTHOR]

• Estimated Curie depth and surface heat flow values using aeromagnetic data. • Curie-Moho depth difference (−5 to −25 km) suggests lower crust to be paramagnetic. • Anomalous thermal structure is due to radioactive sources in the upper crust. Evaluation of the crustal magnetisation through depth to the bottom of the magnetic sources (DBMS; Curie depth) offers an interesting possibility for examining the geodynamics and thermo-tectonic evolution of a region. In the present study, aeromagnetic data is used to unravel the DBMS using the modified centroid method for scaling the distribution of sources. The derived DBMS varies between 14 and 35 km, being shallow (14–20) in the nucleus of the Singhbhum Craton and the southeast of the Chhotanagpur Gneissic Complex. The western part of the Singhbhum Craton is found to have moderate DBMS (20–26 km), whereas deeper depths (26–32) are observed in the south-west Chhotanagpur Gneissic Complex and Eastern Ghats Mobile Belt. The proxy surface heat flow derived from DBMS broadly varies in the range of 40–125 mW/m2 being high (90–125 mW/m2) in the northern part of the Singhbhum nucleus and south-eastern part of the Chhotanagpur Gneissic Complex, moderate (∼70 mW/m2) in the western part of the Singhbhum Craton and Singhbhum Mobile Belt and the south-western part of the Chhotanagpur Gneissic Complex, and low (40–70 mW/m2) in the Eastern Ghats Mobile Belt and Bengal basin. The DBMS-Moho depth difference varies between −5 to −25 km, suggesting that the lowermost part of the crust beneath the eastern Indian shield is paramagnetic. The DBMS lying much above the Moho indicates a crustal extension event that accommodates the exhumation of metamorphic massifs that were buried deep. Else the recurring tectono-magmatic processes have profusely changed the thermal state of the crust. Thermally active sub-continental mantle, substantial mafic–ultramafic crustal-scale intrusions, association with mineralization, migmatization, faulting and extensive folding, and heat-producing radioactive sources (granitoids) in the upper crust are the possible reasons for anomalous crustal thermal structure beneath the eastern Indian shield. [ABSTRACT FROM AUTHOR]

Kıta içi mantodan gelen ısı akısı ile radyojenik ısı oluşumu bileşenlerini birbirlerinden ayırmak genel olarak kolay değildir. Yüzey ısı akısı iki bileşenden oluşur. Birincisi, üst kabuktaki radyojenik ısı kaynakları, ikincisi ise üst manto ve alt kabuk kaynaklı ısı akısıdır. Bu çalışmada, Kırşehir Masifi'nin ısı akısı ve radyojenik ısı üretimi ve bunun jeolojik kaynakları araştırılmıştır. Inceleme alanındaki havadan manyetik verilerden Curie noktası derinlikleri hesaplanmış, ortam homojen ve izotrop kabul edilerek jeotermal gradyent değerleri oluşturulmuştur. Daha sonra sahadan alınmış kayaç örneklerinin ısı iletim değerleri kullanılarak bölgenin ısı akısı hesaplanmış ve bu değerin çalışma alanı için 53 mWm-2 ile 108 mWm-2 değerleri arasında değişim gösterdiği saptanmıştır. Ayrıca, Kırşehir Masifi üzerinde önceden derlenmiş olan havadan spektral gamma-ray verileri kullanılarak radyojenik ısı üretimi haritası oluşturularak çalışma alanının radyojenik ısı üretimi hesaplanmış ve bu değerin 0.62 µWm-3 ile 5.68 µWm-3 arasında kaldığı saptanmıştır. Isı akısı ve radyojenik ısı üretim haritalarının birlikte değerlendirilmesi sonucunda bölgenin ortalama ısı akısı değerlerinin %60-92'sinin manto kaynaklı, %8-38'sinin ise radyojenik kaynaklı olduğu hesaplanmıştır. Çalışma alanındaki radyojenik ısı üretimi, beklenildiği üzere, genel olarak bölge-deki genç granitoyidlerde yüksek anomali değerleri sunmuştur.

We have determined the depth of the Curie isotherm in the United Arab Emirates (UAE) using a modified centroid method based on the fractal distribution of sources. The derived spatial coverage of Curie depths and geothermal gradients are consistent with the geothermal gradients derived from the bottom hole temperatures measured in exploration wells and reveal three NNE–SSW to NE–SW-trending regions of shallow Curie depths. These are: (1) the north-western offshore region of the UAE with Curie depths of 11–25 km; (2) in central UAE ranging from the Shah field in south-central regions of the UAE to the northern offshore region of Dubai, with Curie depths of 10–25 km, high geothermal gradients of 22.1–55.3 °C/km, and high heat flows of 55.3–138.3 mW/m2; and (3) in the eastern region of the UAE from Al Ain to Dibba and the Gulf of Oman, with medium Curie depths of 25–30 km. These regions of shallow Curie depths are flanked by two N S to NE–SW-trending regions of deeper Curie depths between 35 and 50 km with low geothermal gradients and heat flows of 11.1–15.8 °C/km and 27.8–39.5 mW/m2 respectively. We interpreted these regional NE–SW trends to be related to tectonic terranes composed of magmatic arcs and microcontinental fragments that have amalgamated to form the crust beneath the UAE. In addition, many large hydrocarbon fields are located immediately above or on the margins of these shallow Curie depth zones, suggesting that the shallow Curie depth could have played a critical role in the maturation, migration, and entrapment of hydrocarbons in the UAE. Furthermore, since these zones delineate areas of high heat flow (>100 mW/m2) and high geothermal gradients (∼40 °C/km) they represent areas in which future geothermal exploration could be focused. • Determined the depth of the Curie isotherm in the United Arab Emirates. • Revealed three NNE–SSW to NE–SW-trending zones of shallow Curie depths (10–25 km). • Three trending zones delineate areas of high heat flow and high geothermal gradients. • Potential geothermal exploration areas are identified. • Many oilfields are located above or flanks of areas with shallow Curie depths. [ABSTRACT FROM AUTHOR]

The Arabian shield is a Precambrian complex of igneous and metamorphic rocks located approximately one-third of the way across the western Arabian Peninsula, with uncommon exposures along the Red Sea coast. We used aeromagnetic data acquired by others over the past several decades to estimate the depth to the Curie temperature isotherm throughout this region. Our goal was to further understand the lithospheric structure, thermal activity, and seismicity to assist in geothermal exploration. We also compared the Curie temperature isotherm with the crustal thickness to investigate the possibility that mantle rocks are magnetic in some parts of the Arabian shield. Depths to the Curie isotherm were estimated by dividing the regional aeromagnetic grid into 26 overlapping windows. Each window was then used to estimate the shape of the power spectrum. The windows had dimensions of 250 × 250 km to allow investigation of depths as deep as 50 km. The results show the presence of a Curie isotherm at a depth of 10–20 km near the Red Sea, increasing to 35–45 km in the interior of the Arabian shield. The Curie isotherm generally lies above the Moho in this region but deepens into the mantle in some locations, notably beneath the Asir Terrane. [ABSTRACT FROM AUTHOR]

The Curie surface interpreted from magnetic data through spatial frequency domain techniques is used to provide information on the thermal structure of Borborema Province. The Borborema Province is part of the neoproterozoic collision of an orogenic system situated between the São Francisco-Congo and São Luís-West Africa cratons, which formed the Gondwana Supercontinent. The Curie surface of Borborema Province varies from 18 to 59 km, which reveals the complexity in the crustal composition of the study area. The thermal structure shows different crustal blocks separated by the main shear zones, which corroborates the evolution model of allochthonous terranes. The Curie surface signature for the west portion of Pernambuco Shear Zone may indicate processes of mantle serpentinization, once the Curie isotherm is deeper than Mohorovic discontinuity. In this region, the amplitude of Bouguer anomaly decreases, which corroborates long wavelength anomaly observed in the magnetic anomaly. We interpreted this pattern as evidence of the Brasiliano-Pan-Africano's subduction/collision event. Earthquakes in the region are concentrated mainly in shallow Curie surface regions (less resistant crust) and in transition zones between warm and cold blocks. We calculated the horizontal gradient of the Curie depth to emphasize the signature of contact between the thermal blocks. These regions mark possible crustal discontinuities, and have high correlation with orogenic gold occurrence in the study area. [ABSTRACT FROM AUTHOR]

The Eastern and Southeastern Asian regions witness the strongest land-ocean and lithosphere-asthenosphere interactions. The extreme diversity of geological features warrants a unified study for a better understanding of their geodynamic uniqueness and/or ubiquity from a regional perspective. In this paper we have explored a large coverage of potential field data and have detected high resolution Moho and Curie depths in the aforementioned regions. The oldest continental and oceanic domains, i.e. the North China craton and the Pacific and Indian Ocean have been found thermally perturbed by events probably linked to small-scale convection or serpentinization in the mantle and to numerous volcanic seamounts and ridges. The thermal perturbation has also been observed in proximity of the fossil ridge of the western Philippine Sea Basin, which shows anomalously small Curie depths. The western Pacific marginal seas have the lowest Moho temperature, with Curie depths generally larger than Moho depths. The contrary is true in most parts of easternmost Eurasian continent. Magmatic processes feeding the Permian Emeishan large igneous province could have also been genetically linked to deep mantle/crustal processes beneath the Sichuan Basin. The regionally elongated magnetic features and small Curie depths along the Triassic Yangtze-Indochina plate boundary suggest that the igneous province could be caused by tectonic processes along plate margins, rather than by a deep mantle plume. At the same time, we interpret the Caroline Ridge, the boundary between the Pacific and the Caroline Sea, as a structure having a continental origin, rather than as hotspot or arc volcanism. The surface heat flow is primarily modulated by a deep isotherm through thermal conduction. This concordance is emphasized along many subduction trenches, where zones of large Curie depths often correspond with low heat flow. Local or regional surface heat flow variations cannot be faithfully used in inferring deep thermal structures, which can be better constrained overall through Curie depths detected from surface magnetic anomalies. [ABSTRACT FROM AUTHOR]

The study area includes the most important carbonatite and kimberlite complexes in Brazil, located in the Brazilian states of Goiás and Minas Gerais. The central portion of this area involves the Azimuth 125° lineament (Az 125°) that consists of an extensive set of faults (oriented in the NW–SE direction) that served as a conduit for magma ascent. This lineament is the main structural feature associated with these complexes. The Goiás (GAP) and Alto Paranaíba (APAP) Alkaline Provinces occur along the Az 125° and include highly economically valuable mineralizations. In this study, we aim to map the depth to the curie isotherm (or Curie Point Depths: CPD) of the study area (mainly the Gap and APAP regions) based on spectral analysis of aeromagnetic data. The CPD estimations were achieved from a spectral approach known as the centroid method, providing the relationship between the spectra of magnetic anomalies and the depths of the magnetic source of a 2-D magnetic data. The CPD estimates from approximately 500 overlapping blocks vary from 7 km to 40 km deep. The shallower depths are related to the GAP and APAP regions, and the deeper ones are related to the São Franciscana Plate. The Curie depths related to the Az 125° are between 30 km and 15.7 km deep. According to the results, the GAP and APAP intrusive bodies have shallower roots the major faults of the Az 125°. [ABSTRACT FROM AUTHOR]

Compared to the northern South China Sea continental margin, the deep structures and tectonic evolution of the Palawan and Sulu Sea and ambient regions are not well understood so far. However, this part of the southern continental margin and adjacent areas embed critical information on the opening of the South China Sea (SCS). In this paper, we carry out geophysical investigations using regional magnetic, gravity and reflection seismic data. Analytical signal amplitudes (ASA) of magnetic anomalies are calculated to depict the boundaries of different tectonic units. Curie-point depths are estimated from magnetic anomalies using a windowed wavenumber-domain algorithm. Application of the Parker–Oldenburg algorithm to Bouguer gravity anomalies yields a 3D Moho topography. The Palawan Continental Block (PCB) is defined by quiet magnetic anomalies, low ASA, moderate depths to the top and bottom of the magnetic layer, and its northern boundary is further constrained by reflection seismic data and Moho interpretation. The PCB is found to be a favorable area for hydrocarbon exploration. However, the continent–ocean transition zone between the PCB and the SCS is characterized by hyper-extended continental crust intruded with magmatic bodies. The NW Sulu Sea is interpreted as a relict oceanic slice and the geometry and position of extinct trench of the Proto South China Sea (PSCS) is further constrained. With additional age constraints from inverted Moho and Curie-point depths, we confirm that the spreading of the SE Sulu Sea started in the Early Oligocene/Late Eocene due to the subduction of the PSCS, and terminated in the Middle Miocene by the obduction of the NW Sulu Sea onto the PCB. [ABSTRACT FROM AUTHOR]