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Spectral analysis of NAMAG magnetic data enabled us to estimate depths to the Curie isotherm along the Pacific-North America plate boundary. The estimated depths for the Gulf of California, and southern Baja California peninsula, correlate quite well with the depths to the Moho available from previous studies based on receiver function, and seismic refraction. In northernmost Baja California, and southwestern USA no correlation is observed between depths to the Curie isotherm and depths to the mantle obtained from receiver function analysis. Depths to the Curie isotherm are shallower. Along the coastal plains of Sonora and Sinaloa, differences between receiver function based Mantle depths and Curie depths are equally large. However, there is more consistency with depths established by seismic refraction studies. Four zones with shallow Curie isotherm are identified in southern Gulf of California (GS1, GS2, GS3, and GS4). GS1 is located at the Gulf of California mouth. The Alarcon rise is located between GS1 and GS2. Pescaderos Basin is located northwest of GS2. GS3 stretches from the Carmen Basin to the Farallon Basin. GS4 extends from Tiburon Island up to northern Guaymas Basin. Northernmost shallow Curie depth zone (GN1) comprises Upper and Lower Delfin Basins, as well as the Consag and Wagner Basins. A northern prolongation also covers Pinacate Volcanic center. The southern shallow Curie isotherm zones are associated with lithospheric-asthenospheric material upwelling zones. GN1 also includes a convective component related to the younger magmatism of the Pinacate Volcanic Field. Deeper Curie depths are found at southern Baja California peninsula, interpreted as associated with thicker continental or stretched crust. It is possible that the crust is underlain or underplated by magnetic oceanic crust as suggested by satellite magnetic anomalies centered at the Magdalena shelf. A contrasting pattern features northern Baja California: deep Curie zones to the west contrasting with relative shallower Curie isotherm areas to the east. The prolongation towards the peninsula of the extinct Shirley transform fracture zone roughly separates the two domains observed along the peninsula, and suggests that the Curie isotherm along the peninsula is controlled by differences subduction of the Guadalupe and Magdalena microplates. Major differences pointed out between northern and southern Gulf of California might indicate that subduction also played a key role at the beginning of the opening of the Gulf of California, however, currently, the Curie pattern is controlled by the rifting processes (shallow Curie zones correlating quite well with the rift basins and the lithosphere-asthenosphere upwelling material).

We estimated the Curie depth using magnetic anomalies in the tectonically complex central Indian shield. The modified centroid method for the scaling distribution of sources is applied to aeromagnetic data and satellite magnetic data (EMAG2) to estimate the Curie depths. We selected 80% overlapping with a window length of 300 × 300 km2 for Curie depth estimation. The estimated Curie depths are 22–46 km being shallower in the Bastar craton, northern end of the Aravalli-Delhi fold belt, and eastern part of Central Indian tectonic zone in the Deccan Volcanic Province. Deeper Curie depths are found in the eastern parts of the Aravalli-Delhi fold belt, Deccan Volcanic Province to the south of Tapti basin, parts of the Ganga and Vindhyan basins. The heat flow values estimated from the Curie depths vary from 30 to 90 mW/m2 being higher are in the northern part covering the Aravalli-Delhi fold belt and the Ganga basin and low heat flow values in the remaining study region. The computed thermal lithospheric thickness ranges 62–120 km, being 62 km thin in the Vindhyan basin, 68 km in the Aravalli-Delhi fold belt, and 73 km in the Bastar craton. We noticed a relatively thick thermal lithospheric thickness of 99 km beneath the foreland Ganga basin and 100 km in the Bundelkhand craton. The thermal lithosphere beneath the Deccan Volcanic Province is found to have a thickness ~ 120 km beneath central India, which is interpreted as due to the rapid cooling of the lithosphere after Reunion plume activity. Probably, the plume activities in the past could have modified the thermal lithospheric structure beneath central India. The upper mantle in the Deccan Volcanic Province to the south of the Tapti basin and the Aravalli-Delhi fold belt show magnetic character.

The energy of Egypt is generally derived from petroleum products. However, advancements in the development of the generation capacity using sustainable and renewable resources, for example, solar, wind and geothermal resources and investment in nuclear power plants are planned. The geology and structure setting of Egypt affirms that reasonable geothermal resources are available, particularly along the Gulf of Suez, the Red Sea, the Western Desert and parts of the Nile Valley. The main objective of this research is to develop a geothermal favourability map of Egypt, which may be considered as a screening tool for the assessment of optimal areas for geothermal development. Digital data layers and maps were employed in a GIS model to select the most promising areas for geothermal potentiality. The ArcGIS model includes six thematic layers: distance to faults, Bouguer anomaly, distance to seismic activity, Curie depth, heat flow, and temperatures at different depths. The validation of the generated geothermal favourability map was performed by a comparison with thermal water wells and hot springs. Generally, the most encouraging zones for geothermal probability in Egypt are located near the shorelines of the Gulf of Suez and the Red Sea.

A prominent positive gravimetric and magnetic anomaly stands out in the region of the Guadalquivir-Portimao 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 Portimao Banks, the Guadalquivir-Portimao 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-Portimao 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-Portimao 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.

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/m2 respectively. Thus the calculated average geothermal gradient and heat flow for this area are 22.4886 °C/Km and 52.6012 mW/m2 respectively. Since the value obtained from this work is below 100 mW/m2 which is the minimum standard, it then means that this area may not potential be viable as a geothermal source.

Central and Southern Africa is home to major Archean Cratons, flanked by Proterozoic mobile belts. The region is characterized by anomalously high topography and shallow Curie depth (Zb). Factors controlling topography and Zb anomalies in old continental crusts remain poorly understood. In this study, we present high-resolution Moho undulation (Zm) derived with gravity spectral technique. Archean Cratons and Proterozoic belts are mostly characterized by deep Moho (>36 km), whereas the Moho depths in Mozambique belts is mostly shallow (~26 to 41 km). Extremely shallow Zb (

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/m 2. 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.

The depth to the Curie isotherm provides a snapshot into the deep thermal conditions of the crust, which helps constrain models of thermally controlled physical properties and processes. In this study, we present an updated global Curie depth model by employing the equivalent source dipole method to fit the lithospheric magnetic field model LCS-1 from spherical harmonic degree 16 to 100. In addition to the new field mode, we utilise all three vector components and include a laterally variable magnetic susceptibility model. We also employ an improved thermal model, TC1, to supplement the degree 1 to 15 components that are otherwise contaminated by the core field. Our new Curie depth model differs by as much as ±20 km relative to previous models, with the largest differences arising from the low order thermal model and variable susceptibility. Key differences are found in central Africa due to application of a variable susceptibility model, and shield regions, but continents with poor constraints such as Antarctica require additional improvement. This new Curie depth model shows good agreement with continental heat flow observations, and provides further evidence that Curie depth estimates may be used to constrain evaluations of the thermal state of the continental lithosphere, especially in regions with sparse or surface contaminated heat flow observations.

This paper introduces a computational model based on the structural and petrophysical characteristics of the high-enthalpy geothermal reservoirs. Conceptual model of the Sabalan geothermal field is provided through integrating the various exploring information including the structural data, geological data, geophysical models, well logs and field evidences. Heat source is properly estimated by implementing the Curie depth map. The finite element method, adapted to the complex geometry of the model, is used to solve the governing equations. All-important physical and structural properties of the reservoir including the anisotropic and heterogonous permeability distribution, fluid flow through the faults and specific boundary conditions are considered. Optimization analysis is conducted to calibrate the model parameters. Simulated thermodynamic properties of the reservoir are compared with the wellbore measured data to validate the results.

The Curie point depth is of great importance in characterizing geothermal resources. In this study, the Curie iso-depth map was provided using the well-known method of dividing the aeromagnetic dataset into overlapping blocks and analyzing the power spectral density of each block separately. Determining the optimum block dimension is vital in improving the resolution and accuracy of estimating Curie point depth. To investigate the relation between the optimal block size and power spectral density, a forward magnetic modeling was implemented on an artificial prismatic body with specified characteristics. The top, centroid, and bottom depths of the body were estimated by the spectral analysis method for different block dimensions. The result showed that the optimal block size could be considered as the smallest possible block size whose corresponding power spectrum represents an absolute maximum in small wavenumbers. The Curie depth map of the Sabalan geothermal field and its surrounding areas, in the northwestern Iran, was produced using a grid of 37 blocks with different dimensions from 10 × 10 to 50 × 50 km2, which showed at least 50% overlapping with adjacent blocks. The Curie point depth was estimated in the range of 5 to 21 km. The promising areas with the Curie point depths less than 8.5 km are located around Mountain Sabalan encompassing more than 90% of known geothermal resources in the study area. Moreover, the Curie point depth estimated by the improved spectral analysis is in good agreement with the depth calculated from the thermal gradient data measured in one of the exploratory wells in the region.

The Makran subduction wedge as one of the largest subduction complexes has been forming due to the Arabian oceanic lithosphere subducting beneath the Lut and the Afghan rigid block microplates. To better visualize the subducting oceanic crust in this region, a geophysical model of magnetic susceptibility from an airborne magnetic survey (line spacing about 7.5 km) over the Makran zone located at southeast of Iran is created to image various structural units in Iran plate. The constructed geophysical model from the 3D inverse modeling of the airborne magnetic data indicates a thin subducting slab to the north of the Makran structural zone. It is demonstrated that the thickness of sedimentary units varies approximately at an interval of 7.5–11 km from north to south of this zone in the Iranian plate, meanwhile the curie depth is also estimated approximately

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.

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 Sao Francisco-Congo and Sao Luis-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.

Convergence between the Eurasian and Arabian plates formed the Zagros orogenic belt between Late Cretaceous and Pliocene as a relatively young and active fold-thrust belt in Iran. The structural geology along Ahvaz to Isfahan route across Zagros is investigated employing magnetic data in order to determine the crustal structure in the collision zone of the two Palaeo-continents. Airborne magnetometry data with a line space of survey of 7.5 km have been used to image the variations of the apparent magnetic susceptibility along this route. At first the airborne data were stably 500-m downward continued to the ground surface in order to enhance subtle changes of the Earth's magnetic field. Then 3D inverse modeling of magnetic data was implemented, while the cross section of the magnetic susceptibility variations along the route was mapped down to a depth of 100 km. The acquired magnetic susceptibility model could appropriately predict the observed magnetic data as well. In addition, the analytic signal filter was applied to the reduced-to-pole magnetic data leading to the determination of active faults in Zagros fold-thrust belt (ZFTB) structural zone based upon the generated peaks. Some probable locations of fault events were also suggested in Sanandaj–Sirjan Zone (SSZ). The locations of faults correspond well to the magnetic susceptibility variations on the inverted section. Probable direction, slope and depth extension of these faults were also plotted on the magnetic susceptibility model, showing an intensively tectonized zone of the SSZ. The main difference between two domains is that the Eurasian plate seems to contain high magnetic susceptible materials compared to the Arabian plate. The recovered model of the apparent magnetic susceptibility values indicated that the average thickness of the non-magnetic sedimentary units is about 11 km and the Curie depth locates approximately at depth of 24 km for the whole studied area.

The Curie depth is the depth at which the crust and uppermost mantle cease to be ferromagnetic or ferromagnetic, the main cause of crustal magnetism, due to the action of geothermal effects. One method to estimate the Curie depth for Australia is to map the base of magnetisation derived from observations of magnetic intensity. We have used a nonlinear direct sampling inverse technique to fully explore the parameter space of a fractal forward model of magnetisation. This produces an ensemble of models that allow us to produce maps of both the maximum depth of magnetisation and its uncertainty for Australia. The base of magnetisation varies significantly across the continent, between 10 and 70 km depth, with an uncertainty of 7–10 km. The variations in magnetisation depth conform with the boundaries of geological provinces due to their differing magnetic properties: In general, cratons and older provinces generally show a deeper base of magnetisation results and hence may be inferred to have deeper Curie depths, reflecting that these areas are on the whole cooler. We also find general agreement in our results with known geothermal anomalies.

The high-amplitude wide magnetic anomaly that covers a large area of the north-eastern – central Adriatic Sea in the Croatian offshore is ∼100 km wide and extends NW–SE for ∼350 km. The anomaly is located between the Dinarides and Apennines chains, in an interesting geodynamic scenario. The presence of intruded gabbroid rocks in the Croatian archipelago also contributes to making this intriguing and still not extensively investigated anomaly potentially significant to the geologic and geophysical context in which it is located. In this work, we model the Bouguer and magnetic anomalies across the Adriatic Sea. The 2D geophysical modeling was produced across four cross sections considering surface heat flow data to calculate the Curie depth. The magnetic susceptibilities and densities used for the synthetic bodies are in agreement with the literature and with those derived by previous models. The results suggest the presence of an uplifted magnetized basement with high magnetic susceptibility (0.075 SI units) to be the main contributor to the observed magnetic anomaly. This magnetic susceptibility is interpreted as representative of a gabbroid-intruded basement. The high-susceptibility basement is in lateral continuity with a relatively low susceptibility basement (0.025–0.038 SI units). The results of the geophysical modeling are compared with a conceptual geological model realized from the integration of surface, well and geophysical data, the latter concerning seismic, tomographic, magnetic and gravimetric anomalies and heat flow data. These data have been merged in an integrated data-base using MOVE software, and the geophysical modeling was performed using GM-SYS. The comparison allowed to confirm the hypothesis that the magnetic anomaly is related to the basement and to its position in the complex geodynamic evolution of the Apennines–Adriatic–Dinarides system.

The study area includes the most important carbonatite and kimberlite complexes in Brazil, located in the Brazilian states of Goias 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 Goias (GAP) and Alto Paranaiba (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 Sao 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°.

An estimate of depths to the bottom of magnetic sources (DBMS) in the upper part of Sokoto Basin, north-west Nigeria has been made from the modified centroid method based on a fractal source distribution of magnetic sources and spectral analysis of aeromagnetic data. DBMS is used as an estimate of the Curie-point depth and hence a proxy for temperature at depth. Aeromagnetic maps covering an area bounded by latitudes 12.5° N and 13.5° N and longitudes 4.0° E and 6.0° E were digitized at an equal spacing of 1 km. Six profiles were subsequently mapped out on the magnetic data covering different geological parts for the purpose of spectral centroid analysis. The result shows that the DBMS varies between 11.37 km and 28.18 km. Consequently, geothermal gradient varies between 20.58 °C/km and 51.02 °C/km, while the ensuing heat flows vary between 51.45 mW/m 2 and 127.55 mW/m 2 . The thermal structure of the earth's crust is one of the main parameters controlling geodynamic processes. This study is crucial for quantitative understanding of the geo-processes and rheological/rock-physics parameters in the study area.

In this paper, data of gravimetry, aeromagnetic survey, and surface heat flow are utilized in a combined manner to investigate the crustal thickness, Curie surface, and lithospheric thermal state beneath the Junggar Basin and adjacent Mountain Ranges. The Moho depth, Curie depth, and thermal lithospheric thickness are found to be 38–52 km, 32–50 km, and 120–260 km, respectively. The Moho and Curie surface present a rough inverse correspondence between each other. In the Tianshan and Altai Mountain Ranges, Moho interface is deep but Curie surface is shallow. In the Junggar Basin, Turpan Basin, and Yili Basin, the situation is in reverse. The uppermost mantle in the Central Depression and Eastern Uplift of the Junggar Basin, the Turpan Basin, the Yili Basin, as well as the north-west area off Fuhai is investigated to have been magnetized. The aeromagnetic anomalies and the Curie surface in the Junggar Basin surprisingly reveal that the northward subduction of the north Tarim block/slab under the Junggar Basin accompanied by the uplift of the Tianshan Mountain Range. Also, in response to the northward movement, the rigid Central Depression of the Junggar Basin extruded from its east and west sides. The westward extrusion is manifested by the West Uplift of the western Junggar Mountain Range.

The depth to the bottom of the magnetic sources (DBMS) has been estimated from the aeromagnetic data of Central India. The conventional centroid method of DBMS estimation assumes random uniform uncorrelated distribution of sources and to overcome this limitation a modified centroid method based on scaling distribution has been proposed. Shallower values of the DBMS are found for the south western region. The DBMS values are found as low as 22 km in the south west Deccan trap covered regions and as deep as 43 km in the Chhattisgarh Basin. In most of the places DBMS are much shallower than the Moho depth, earlier found from the seismic study and may be representing the thermal/compositional/petrological boundaries. The large variation in the DBMS indicates the complex nature of the Indian crust.

The geothermal regime beneath the Barramiya–Red Sea coast area of the Central Eastern Desert of Egypt has been determined by using the Curie point depth, which is temperature dependent. This study is based on the analysis of aeromagnetic data. The depth to the tops and centroid of the magnetic anomalies are calculated by power spectrum method for the whole area. The result of this investigation indicates, two new maps of the Curie point depth (CPD) and the surface heat flow (q) maps of the study area. The coastal regions are characterized by high heat flow (83.6 mW/m2), due to the geothermic nature of the region, and shallow Curie depth (22.5 km), where (CPD) depends on the tectonic regime and morphology in the eastern part of the area. The western portion of the studied area has a lower heat flow (

Over 50 magnetic bottom depths derived from spectra of magnetic anomalies in Eastern Egypt along the Red Sea margin show variable magnetic bottoms ranging from 10 to 34 km. The deep magnetic bottoms correspond more closely to the Moho depth in the region, and not the depth of 580 °C, which lies significantly deeper on the steady state geotherms. These results support the idea of Wasilewski and coworkers that the Moho is a magnetic boundary in continental regions. Reduced-to-pole magnetic highs correspond to areas of Younger Granites that were emplaced toward the end of the Precambrian. Other crystalline Precambrian units formed earlier during the closure of ocean basins are not strongly magnetic. In the north, magnetic bottoms are shallow (10–15 km) in regions with a high proportion of these Younger Granites. In the south, the shoaling of the magnetic bottom associated with the Younger Granites appears to be restricted to the Aswan and Ras Banas regions. Complexity in the variation of magnetic bottom depths may arise due to a combination of factors: i) regions of Younger (Precambrian) Granites with high magnetite content in the upper crust, leaving behind low Curie temperature titanomagnetite components in the middle and lower crust, ii) rise in the depth of 580 °C isotherm where the crust may have been heated due to initiation of intense magmatism at the time of the Red Sea rifting (~ 20 Ma), and iii) the contrast of the above two factors with respect to the neighboring regions where the Moho and/or Curie temperature truncates lithospheric ferromagnetism. Estimates of fractal and centroid magnetic bottoms in the oceanic regions of the Red Sea are significantly below the Moho in places suggesting that oceanic uppermost mantle may be serpentinized to the depth of 15–30 km in those regions.

Sinai Peninsula is considered as a unique region in the world due to its geographical location, tectonic and thermal activities. It is located geographically at the crossroads of Europe, Asia, and Africa constituting a triple junction point between the three continents. It is also characterized by thermal manifestations represented by several hot springs with varied temperatures (30–70 °C). Most of these hot springs are located along the shoreline of the Gulf of Suez. In this study, we aim to map the Curie depth isotherm surface for Sinai Peninsula based on the analysis of ground magnetic data. Spectral analysis technique will be used to estimate the boundaries (top and bottom) of the magnetized crust. The depths obtained for the bottom of magnetized crust are assumed to correspond to Curie point depths where the magnetic layer loss its magnetization. Results of this study indicate that the shallow Curie depths (~ 15–18 km) are located at the southern part of Sinai Peninsula and along the shoreline of the Gulf of Suez and depths increase (22–25 km) towards the central and north western portions of Sinai Peninsula. The whole average Curie depth point of Sinai Peninsula is about 20 km. Generally, the shallow depths to Curie isotherm indicate that Sinai Peninsula is a promising area for further geothermal exploration particularly near the eastern side of the Gulf of Suez.

I investigate large-scale deep crustal structures of the Nankai subduction zone and neighboring region using regional magnetic and gravity anomalies, heat flow measurements, and earthquake hypocenters. It is found that ages, dip angles, and geothermal states of the subducting slab have direct influences on mantle wedge serpentinization. The weakest serpentinization observed in the Nankai forearc region is associated with the youngest downgoing plate of the Shikoku Basin. Conspicuous gravity anomalies identified in the forearc region are coincidental spatially with magnetic anomalies after the reduction to the pole, a mathematical procedure that helps relocate magnetic sources and boundaries, and allows us to more easily interpret magnetic data. It is argued that these patches of magnetic and gravity anomalies are caused by the same sources of anomalous density and magnetization, and are linked directly to preexisting structures such as magnetic anomalies and their boundaries in the subducting oceanic crust. Since the gravity and magnetic anomaly patches are found to be closely related to interplate seismogenic behaviors in the Nankai subduction zone, I suggest that major magnetic boundaries in the Shikoku Basin are likely weak places for slab tears that trigger seismic segmentations along the subduction zone. Application of the Parker–Oldenburg algorithm to Bouguer gravity anomalies yields a 3D Moho topography. Curie-point depths are also estimated from the magnetic anomalies with reduction to the pole using a windowed wavenumber-domain algorithm. Window sizes are found to have little effects on the average Curie-point depths other than lowering lateral resolutions. A wide zone of deep Curie depths is identified in southwest Japan, relating to strong influence from the subduction of the relatively young and warm Shikoku Basin crust of the Philippine Sea plate. Curie depths so obtained can be correlated well with heat flow measurements, which cluster around a theoretical curve when the average thermal conductivity is about 3.0 W/(m °C). Using constraints from both Curie depths and heat flow, I also model the shallow geothermal field of the subduction zone. Earthquake hypocenters plotted against Moho and Curie depths and geothermal fields on three transects confirm early studies that downdip limits of seismogenic zones along the Nankai plate boundary do not extend down to the island arc Moho and their temperatures are more or less close to 350 °C. Geothermal field has direct influences on earthquake distributions in the overriding island arc and accretionary prism, within the subducting oceanic lithosphere, and along the interplate boundary.

The basal depth of the magnetic layer (Curie point depths) of Bulgarian territory was calculated using geomagnetic field observation and the variations of this border were mapped for the first time. The adopted computational method transforms the spatial data into the frequency domain and provides a relationship between radially averaged power spectrum of the magnetic anomalies and the depths to the magnetic sources. The magnetic layer bottom thus obtained has “normal” (28–32 km) values in the Moesian platform and central part of Bulgaria which are the relatively most stable regions of the investigated territory. In the Moesian platform CPD and Moho are very close but the magnetic layer's bottom is still marked as a thermal boundary. In the southern part, calculated depths gradually reach the minimal values of the derived Curie isotherm (up to 14–16 km) with relatively high gradient. According to the results from geothermal modeling and paleomagnetic investigations, magnetic layer's bottom of the Bulgarian territory corresponds to different Curie temperatures. They vary from 400–425 °C in the regions of Rila-Rhodope unit, up to 550–600 °C in the Moesian platform, West- and East-Balkan unit. The obtained results comprise useful information concerning regional estimates of the correlation between different geophysical and geological characteristics of the earth's crust of the Bulgarian territory.

Estimating depth to the bottom of the magnetic crust (synonymously called the Curie isotherm) on a regional scale from long wavelength magnetic anomalies requires that large areas of survey data be used for the calculations. There is still no consensus on the minimum survey area required to arrive at a reliable estimate of the Curie isotherm depth. From the available aeromagnetic data over India, depth to the Curie isotherm is estimated using spectral techniques. We found that the significant spectral maxima required to calculate the depth to the Curie isotherm existed only for 4° × 4° blocks in southern peninsular India up to 18 °N latitude and for 5° × 5° blocks for the rest of the region in Central India. As aeromagnetic data coverage over India is incomplete, we also calculate the magnetic crustal thickness from the lithospheric model of the CHAMP satellite data for the whole country, using an iterative forward modeling approach. The calculated Curie isotherm is shallow in the mobile belts and deeper in the cratons in both the derivations. As the Curie isotherms calculated from the two data sets collected at very different altitudes using totally different techniques, match reasonably well, it lends credence to the methodology adopted. The derived Curie isotherm depth map is in accordance with the basic structural trend of the major tectonic units within the Indian subcontinent. A comparison is made of the calculated Curie isotherm depth with Moho depths along available DSS profiles over India and it is found that the Curie depth is generally shallower than the Moho depth implying that it possibly represents a thermal boundary rather than a compositional change. Further, we find that high magnitude earthquakes are associated with high gradients in Curie depth.

This work deals with 2D thermal modeling in order to delineate the crustal thermal structure of central India along two Deep Seismic Sounding (DSS) profiles, namely Khajuriakalan–Pulgaon and Ujjan–Mahan, traversing the Narmada-Son-Lineament (NSL) in an almost north–south direction. Knowledge of the crustal structure and P-wave velocity distribution up to the Moho, obtained from DSS studies, has been used for the development of the thermal model. Numerical results reveal that the Moho temperature in this region of central India varies between 500 and 580 °C. The estimated heat flow density value is found to vary between 46 and 49 mW/m2. The Curie depth varies between 40 and 42 km and is in close agreement with the Curie depth (40±4 km) estimated from the analysis of MAGSAT data. Based on the present work and previous work, it is suggested that the major part of peninsular India consisting of the Wardha–Pranhita Godavari graben/basin, Bastar craton and the adjoining region of the Narmada Son Lineament between profiles I and III towards the north and northwest of the Bastar craton are characterized with a similar mantle heat flow density value equal to ∼23 mW/m2. Variation in surface heat flow density values in these regions are caused by variation in the radioactive heat production and fluid circulation in the upper crustal layer.

The basal depth of the outer layer with internal magnetic sources was calculated from magnetic data available within a roughly 500 km wide and 1200 km long area, running from central Germany to southern Italy. The dataset, deriving from different aeromagnetic surveys, is reduced to the reference altitude of 3000 m a.s.l. and a reference year of 1980.0. The adopted method, which transforms the spatial data into the frequency domain, provides a relationship between the two-dimensional spectrum of the magnetic anomalies and the top and centroid depths of the magnetic sources. The magnetic layer bottom depth (MLBD) thus obtained is 29–33 km deep in the stable areas (central Europe Variscan units, Corsica–Sardinia Variscan block) and corresponds to the Moho, having an average temperature of 560 °C. From the Alps to the Apennines, MLBD ranges between 22 and 28 km and is clearly shallower than the Moho. In these units, the wide variation of MLBD appears to be compatible with the presence of shallow magnetised bodies, consisting of lower crustal rocks (Ivrea–Verbano zone), ophiolitic units (Penninic zone and Voltri Massif) and intrasedimentary basic volcanic bodies (Po Basin). An average value of 25 km can be attributed to MLBD, which corresponds to a temperature of 550 °C. In the peri-Tyrrhenian zone and the Ligurian Sea, MLBD is below the Moho, which ranges from 17 to 20 km depth, and it has a temperature matching approximately to the Curie temperature of magnetite (580 °C).

The passive continental margin of western India and the adjacent offshore region are associated with a transitional type thinned crust. It contains several sedimentary basins where substantial recoverable oil/gas reserves exist. The northern Cambay graben, northern and eastern parts of the Bombay offshore and the Konkan coast region that are situated close to western margin exhibit reasonably high heat flow and geothermal gradients beneath which the asthenosphere is upwarped to a depth of 30–70 km. Temperatures at the depth of 3 km are estimated to be in the range of 105–260°C. Curie depth analysis from MAGSAT studies in an area between latitudes 11°N and 19°N and longitudes 65°E and 73°E also indicates a high geothermal gradient of about 30°C/km within the upper crustal column. We suggest that the occurrence of oil and gas in these areas may be due to catastrophic and geodynamic events which took place in the last 130 Ma. India’s super-mobility, continental breakups, possible bolide impact and Deccan volcanic episode at the western margin resulted in substantial lithospheric heating, accompanied by subcrustal melting and rise of isotherms, to eventually enhance the hydrocarbon maturation process. The study indicates that all other sedimentary basins situated on the western margin are also thermally mature and may have high potential for the occurrence of hydrocarbons.

The bottom of the magnetized crust determined from the spectral analysis of residual magnetic anomalies is generally interpreted as the level of the Curie point isotherm. A method to estimate the depth extent of magnetic sources (Curie point depth analysis) was applied to the magnetic anomalies of East and Southeast Asia. Although the geologic and physiographic complexities of this area constrain the method, certain correlations between the Curie point depths and heat flow data are apparent and the Curie point depths are consistent with the tectonic settings. Shallow basal depths of magnetic sources that extend in back-arc regions correspond to high heat flow values. The correspondence of deep basal depths with low heat flow values along the trench axis suggests that they are both related to the subducting plate. We also estimate the Curie point depths from heat flow data using a one-dimensional heat conductive transport model. Good agreement between the Curie point depths derived from heat flow data and magnetic data suggests that the Curie point depth analysis is useful to estimate the regional thermal structure.

One-dimensional spectral analysis of aeromagnetic data over the Anambra Basin, which is a subsidiary depression within the Benue Trough of Nigeria, was made to map the sedimentary thickness variations and the Curie temperature isotherm. Sedimentary thickness (depth to the basement) varies between 0.9 and 5.6 km, while depth to the Curie temperature isotherm varies between 16 and 30 km below the mean sea level. The result also shows that the Curie temperature isotherm within the basin is not a horizontal level surface, but is undulating, and the geothermal gradients associated with it range between 20 and 35 °C/km.

Magnetic modeling of the forearc side of the Tohoku (northeastern Japan) Arc was carried out using spectral analysis of shipborne magnetic data. The original data show anomalies caused by volcanic rocks on the western, shallow side and linear marine magnetic anomalies on the eastern, deeper side throughout the forearc region. As calculated from temperature gradient data of heat flow measurements and deep drilling, the Curie depth is deeper than the Moho on the eastern, deeper side. This suggests that the Moho may correspond to the base of the magnetic layer, because analysis of upper mantle xenolith suites indicates that the upper mantle should be non-magnetic. In addition, the Conrad discontinuity may correspond to the apparent top of magnetic layer because the lower crustal layer would be more mafic than the upper layer. It was estimated by 2D spectral analysis that the magnetic base and surface lie at about 20 km and 10 km respectively. This suggests that the Moho and the Conrad may roughly correspond to the magnetic base and surface. The magnetic anomalies in the Pacific basin are traced towards and over the inner side of the trench, and show a gradual decrease in amplitude, disappearing eventually about 100 km west of the trench. This reflects the descent of the oceanic slab. The 1D spectral analysis indicates that the marine magnetic layer is descending at an angle of about 4° in the Japan Trench, this angle increasing to 20 ° degrees below the coast, where the marine magnetic layer reaches a depth of more than 30 km. This agrees with the seismic reflection data from the trench, and because the magnetic layer can be traced down to a depth of 30 km it may be suggested that the Curie isotherm deepens to more than 30 km just east of the coast.

A correlation study among Pn velocity distribution, surface heat flow and other related thermal parameters for Southern Indian Shield reveals that Pn velocity decreases significantly in the regions where regional heat flow and Moho temperatures are high. These areas are associated with shallow Curie depth and thin lithosphere. The observed variation in Pn velocity beneath Western part of Peninsular India could be explained due to pressure-temperature effect. However, beneath the Cuddapah basin it is not merely due to pressure-temperature difference at upper most mantle but lateral inhomogeniety is also responsible for it.

In order to coordinate available geophysical data on the deep-seated structure with observed heat flow, it has to be borne in mind that the thermal field of the Baikal rift zone is not in a steady-state. A two-dimensional model of the transient temperature field of the lithosphere was constructed by a numerical method for the solution of the energy conservation equation. The authors suggest that asthenospheric upwelling, 250 km wide, was formed on account of roof block detachment. Such a mechanical replacement of the lithosphere by the asthenosphere was simulated by a positive (compulsory) upward movement of the 1200°C isotherm with constant velocity. The duration of this movement was taken as long as 30 m.y., which corresponds to the duration of the first (slow) rifting stage. As soon as the asthenosphere had reached the Mohorovicic discontinuity, its ascending movement on a wide scale ceased, because the density of the crust was less than that of the asthenosphere. Temperature calculations were carried out in the lithosphere above the 1200°C isotherm. This model permits us to reproduce theoretically the present value of the regional heat flow and the Curie depth, when the time passed from the cessation of the upwelling top movement became equal to 3.5 m.y. The last figure corresponds to the duration of the second (fast) stage of rifting. On the regional scale the crust of the rift zone (Sayan-Baikal domal uplift) continues to be heated. Cooling of the crust can only occur at the segments corresponding to the local heat flow anomalies, which are suggested as being produced by dikes. The intrusion time of the dike beneath the southern Baikal is estimated to be 3 m.y.