Curie Depth Research Articles

Variations in Moho and Curie depths and heat flow in Eastern and Southeastern Asia

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.

Tracing the manganese ore accumulations in Sinai Peninsula, Egypt, using magnetic method

In this study, an ideal area known for manganese ore accumulations in Sinai Peninsula has been investigated in detail using geological, laboratory analyses and magnetic tools. The main target is to establish a relationship between the ore accumulations, geology and the subsurface faults (shear structures) which are extending to deeper depths in the basement rocks of the study area and then use it as key for the un-explored areas in the Sinai Peninsula. To achieve this target, a detailed land magnetic survey has conducted to the selected area and later extended to include the whole peninsula. The geological data have obtained from the drilled wells and Egyptian Geological Survey and Mining Authority of Egypt. The geological investigations are including studying the surface geology and interpretation the well logging data to trace the ore mineral distributions along the different depths in the peninsula. The magnetic data has processed using a series of techniques, namely, second vertical gradient, 3D analytical signal, trend analyses, Euler deconvolution, Werner deconvolution and 3D modeling techniques. Also, the Curie depth method has applied along more than 31 grids forming the magnetic map of Sinai Peninsula to study the behavior of geothermal solutions and their effects in the host country rocks and their relationship to the existing ore accumulations. Furthermore, more than 300 rock samples have collected from different sites covering Sinai Peninsula area. These samples were subjected to laboratory measurements of the magnetic susceptibility. The results show that the Curie magnetic depth confirms that these shear structures at the intersection points are extended to deep depths which make as a pass way for the hydrothermal solutions into the host rocks which are probably forming the ore accumulations. The ore mineral accumulations appear to be confined to the carbonate rocks and to the shear zones intersections of the structures which are trending NW–SE and NE–SW directions. The depth to these accumulations was found to be ranging between 300 m at the southern parts to more than 3 km at the northern parts of the Sinai Peninsula. The measured magnetic susceptibility values range between 0.4 SI and 1.8 SI. Five new areas namely; Sharm El Sheikh, Wadi Zaghrah, SW Taba, Libni and Maghara can be prospected in the Sinai Peninsula have the similar conditions which are existing at Abu Zneima known mine area.

Magnetic Signatures and Curie Surface Trend Across an Arc–Continent Collision Zone: An Example from Central Philippines

Ground and aeromagnetic data are combined to characterize the onshore and offshore magnetic properties of the central Philippines, whose tectonic setting is complicated by opposing subduction zones, large-scale strike-slip faulting and arc–continent collision. The striking difference between the magnetic signatures of the islands with established continental affinity and those of the islands belonging to the island arc terrane is observed. Negative magnetic anomalies are registered over the continental terrane, while positive magnetic anomalies are observed over the Philippine Mobile Belt. Several linear features in the magnetic anomaly map coincide with the trace of the Philippine Fault and its splays. Power spectral analysis of the magnetic data reveals that the Curie depth across the central Philippines varies. The deepest point of the magnetic crust is beneath Mindoro Island at 32 km. The Curie surface shallows toward the east: the Curie surface is 21 km deep between the islands of Sibuyan and Masbate, and 18 km deep at the junction of Buruanga Peninsula and Panay Island. The shallowest Curie surface (18 km) coincides with the boundary of the arc–continent collision, signifying the obduction of mantle rocks over the continental basement. Comparison of the calculated Curie depth with recent crustal thickness models reveals the same eastwards thinning trend and range of depths. The coincidence of the magnetic boundary and the density boundary may support the existence of a compositional boundary that reflects the crust–mantle interface.

Heat flow pattern at the Chicxulub impact crater, northern Yucatan, Mexico

Along an east–west profile crossing the Chicxulub impact structure in northern Yucatán, México, Curie depths were obtained from statistical-spectral analysis of a grid of aeromagnetic data (256km wide and 600km long). These depths were corrected for flight height and depth to the sea floor to determine the geothermal gradient, assuming a temperature of 580°C for the Curie temperature. Heat flow was then calculated from the geothermal gradients using a value of 2.67W/m-K for the mean crustal thermal conductivity. The results show a conspicuous heat flow high above on the impact basin. In this location, the heat flow is 80mW/m2 approximately. Available offshore estimates of the depth to the crustal magnetic source bases, on the northern Yucatán platform, and onshore heat flow determination on 8 shallow bore holes, and in a 1511m deep one, support the existence of this major high heat flow anomaly associated with the impact crater. This high heat flow might be related to the impact through: (1) an uplift of the crystalline basement rocks in the center of the crater; and (2) impact induced radioactive element concentration into the crust below the impact structure. Higher thermal conductivities at the lower crust might also play a key role. Available seismological and thermal property data are compatible with these mechanisms.

An airborne magnetometry study across Zagros collision zone along Ahvaz–Isfahan route in Iran

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 7.5km 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 100km. 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 11km and the Curie depth locates approximately at depth of 24km for the whole studied area.

Magnetic signatures of the orogenic crust of the Patagonian Andes with implication for planetary exploration

The Patagonian Andes represent a good scenario of study because they have outcrops of diverse plutonic rocks representative of an orogenic crust on Earth and other planets. Furthermore, metamorphic surface rocks provide a window into deeper crustal lithologies. In such remote areas, satellite and aerial magnetic surveys could provide important geological information concerning exposed and not exposed rocks, but they integrate the magnetic anomalies in areas of kilometres. For the southernmost Andes long wavelength satellite data show clear positive magnetic anomalies (>+100nT) for the Patagonian Batholith (PB), similar as parts of the older martian crust. This integrated signal covers regions with different ages and cooling histories during magnetic reversals apart from the variability of the rocks.To investigate the complex interplay of distinct magnetic signatures at short scale, we have analysed local magnetic anomalies across this orogen at representative sites by decimeter-scale magnetic ground surveys. As expected, the investigated sites have positive and negative local anomalies. They are related to surface and subsurface rocks, and their different formation and alternation processes including geomagnetic inversions, distinct Curie depths of the magnetic carriers, intracrustal deformation among other factors. Whole rock chemistry (ranging from 45 to >80wt.% SiO2 and from 1 to 18wt.% FeOtot.), magnetic characteristics (susceptibilities, magnetic remanence and Königsberger ratios) as well as the composition and texture of the magnetic carriers have been investigated for representative rocks. Rocks of an ultramafic to granodioritic intrusive suite of the western and central PB contain titanomagnetite as major magnetic carrier. Individual magnetic signatures of these plutonic rocks reflect their single versus multidomain status, complex exolution processes with ilmenite lamella formations and the stoichiometric proportions of Cr, Fe and Ti in the oxides. At the eastern margin of the PB the investigated plutons and mafic dykes have been emplaced and equilibrated at 4–6km depth. They do not contain magnetite but include variable amounts of ferrimagnetic monoclinic C4 pyrrhotite, which was formed along fractures zones by a hydrothermal gold-bearing mineralisation. The intensity of their positive magnetic anomalies (up to +220nT) is well correlated with the amount of pyrrhotite (1–4vol.%). In all cases, high resolution ground surveys variations of the magnetic signature down to 20nT could be used to clearly distinguish different rock types on a decimeter scale. Vector magnetometer MOURA designed for martian exploration was successfully used for these surveys and provides results comparable to a commonly used caesium scalar magnetometer. This is important for near future ground surveys on Mars and the Moon.

Magnetic and gravimetric modeling of the central Adriatic region

The high-amplitude wide magnetic anomaly that covers a large area of the north-eastern – central Adriatic Sea in the Croatian offshore is ∼100km wide and extends NW–SE for ∼350km. 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.

Maximum depth of magnetisation of Australia, its uncertainty, and implications for Curie depth

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 70km depth, with an uncertainty of 7–10km. 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.

Imaging three‐dimensional crustal conductivity structures reflecting continental flood basalt effects hidden beneath thick intracratonic sedimentary basin

AbstractA large‐scale array of long‐period magnetic data and a deep‐probing magnetotelluric profile were recorded in the intracratonic Paraná sedimentary basin in central eastern South America, which presents a thick and extensive sedimentary‐magmatic sequence that allows its basement to be investigated only by indirect methods. Integration of the results from both methods showed that the crust beneath the basin presents several quasi‐linear highly conductive channeled zones with limited lateral extent, in coincidence with some of the main tectonic structures recognized at the surface, and a moderate but pervasive lithosphere conductivity enhancement beneath its central part. Upward movement of CO2‐bearing volatiles and magmas precipitating highly conducting mineral phases along discrete subvertical fault zones that served as feeder conduits for Early Cretaceous voluminous continental flood basalts was a likely process responsible for the localized conductivity enhancements. Correlation between some of the linear conductive zones and elongated magnetic anomalies and between the maximum depth occurrence of most of these conductive anomalies and the Curie depth at which crustal rocks lose their magnetism gives strong support to interconnected iron oxides (especially magnetite) and iron sulfides (such as pyrrhotite) as the main conductive sources. The moderate bulk conductivity increase in the crust and upper mantle beneath the central part of the basin is unexpected for a postulated cratonic basement and is tentatively associated with impregnation of the lithosphere by conducting minerals related either to widespread tectonic events in the Ordovician or Late Precambrian or to dispersed magmatic residues of an Early Cretaceous magma differentiation contaminating the entire lithosphere.

Curie Depth Analysis of the Salton Sea Region, Southern California

Aeromagnetic data were analyzed to determine the bottom of magnetic bodies that might be related to the Curie point depth (CPD) by 2D spectral and 3D inversion methods within the Salton Trough and the surrounding region in southern California. The bottom of the magnetic bodies for 55 × 55 km windows varied in depth between 11 and 23 km in depth using 2D spectral methods. Since the 55 × 55 km square window may include both shallow and deep source, a 3D inversion method was used to provide better resolution of the bottom of the magnetic bodies. The 3D models indicate the depth to the bottom of the magnetic bodies varied between 5 and 23 km. Even though both methods produced similar results, the 3D inversion method produced higher resolution of the CPD depths. The shallowest depths (5–8 km) occur along and west of the Brawley Seismic Zone and the southwestern portion of the Imperial Valley. The source of these shallow CPD values may be related to geothermal systems including hydrothermal circulation and/or partially molten material. Additionally, shallow CPD depths (7–12 km) were found in a northwest-trending zone in the center of the Salton Trough. These depths coincide with previous seismic analyses that indicated a lower crustal low velocity region which is believed to be caused by partially molten material. Lower velocity zones in several regions may be related to fracturing and/or hydrothermal fluids. If the majority of these shallow depths are related to temperature, they are likely associated with the CPD, and the partially molten material extends over a wider zone than previously known. Greater depths within the Salton Trough coincide with the base of basaltic material and/or regions of intense metamorphism intruded by mafic material in the middle/lower crust.

Curie Point Depths and Heat Flow of Eastern Anatolia (Turkey)

The bottom of the magnetized crust determined from the spectral analysis of magnetic anomalies is generally interpreted as the level of the Curie point isotherm. The spectral analysis method to estimate the depth extent of magnetic sources was applied to the magnetic anomalies of Eastern Anatolia and compared with the tectonic regime and heat flow data in the region. The Curie point depth of eastern Anatolia ranges from 6 to 24 km. The computed Curie depths and the heat flow values derived by using Curie depths are consistent with the geological and the seismological findings of the region. Shallow Curie point depths and high heat flow values are seen between the Bitlis Suture Zone and the pontides. At the same time, this region might contain a thinner crust than expected.

Crustal magmatism and lithospheric geothermal state of western North America and their implications for a magnetic mantle

The western North American lithosphere experienced extensive magmatism and large-scale crustal deformation due to the interactions between the Farallon and North American plates. To further understand such subduction-related dynamic processes, we characterize crustal structure, magmatism and lithospheric thermal state of western North America based on various data processing and interpretation of gravimetric, magnetic and surface heat flow data. A fractal exponent of 2.5 for the 3D magnetization model is used in the Curie-point depth inversion. Curie depths are mostly small to the north of the Yellowstone–Snake River Plain hotspot track, including the Steens Mountain and McDermitt caldera that are the incipient eruption locations of the Columbia River Basalts and Yellowstone hotspot track. To the south of the Yellowstone hotspot track, larger Curie depths are found in the Great Basin. The distinct Curie depths across the Yellowstone–Snake River Plain hotspot track can be attributed to subduction-related magmatism induced by edge flow around fractured slabs. Curie depths confirm that the Great Valley ophiolite is underlain by the Sierra Nevada batholith, which can extend further west to the California Coast Range. The Curie depths, thermal lithospheric thickness and surface heat flow together define the western edge of the North American craton near the Roberts Mountains Thrust (RMT). To the east of the RMT, large Curie depths, large thermal lithospheric thickness, and low thermal gradient are found. From the differences between Curie-point and Moho depth, we argue that the uppermost mantle in the oceanic region is serpentinized. The low temperature gradients beneath the eastern Great Basin, Montana and Wyoming permit magnetic uppermost mantle, either by serpentinization/metasomatism or in-situ magnetization, which can contribute to long-wavelength and low-amplitude magnetic anomalies and thereby large Curie-point depths.

Estimation of depth to top of magnetic sources using the local-wavenumber approach in an area of shallow Moho and Curie depth — The Red Sea

The local-wavenumber method estimates the depth to a magnetic source based on the spectral content of a single anomaly assuming that the base of the magnetic body is at infinite depth. However, the “infinite-depth” assumption can lead to significant underestimation of the depth to the top of magnetic bodies, especially in areas where the depth to the bottom of the magnetic layer is not large compared to the depth to the top, as would occur in high heat-flow regions and thinned continental margins. Such underestimation of depths has been demonstrated in model studies and using real data with seismic and well control. We evaluated a modification to the local-wavenumber approach to estimate the depth to the top of magnetic sources assuming that the depth to the bottom of the magnetic sources is controlled by the Curie temperature or crustal thickness. We applied this new method to a simple model of a continental margin and to magnetic survey data over the central Red Sea where the Curie isotherm is shallow. The effective structural index of this finite depth extent model is found to increase continuously from the continent to the ocean as the depth to the magnetic basement increases and the depth to the bottom of the magnetic layer decreases. We have also discovered in this study that the local-wavenumber maxima correlate well with major seafloor spreading magnetic reversal epochs in the central Red Sea segment.

Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring - Ekiti State, southwestern Nigeria

Aeromagnetic data of the Ikogosi warm spring region was used to calculate the basal depth of the magnetic layer (Curie point depth) in the region. The warm spring issues from a crossing of fractures from a metasedimentary suite of Effon Psammite formation which form part of the Precambrian basement complex in Nigeria. The adopted computational method transforms the spatial data into the frequency domain and provides a relationship between radially average power spectrum of the magnetic anomalies and the depths to the respective sources. Heat flow density and equivalent depth extent of heat production from radioactive isotopes in the area were also evaluated. The average Curie point depth for the Ikogosi warm spring area is 15.1 ± 0.6 km and centres on the host quartzite rock unit. The computed equivalent depth extent of heat production provides a depth value (14.5 km) which falls within the Curie point depth margin and could indicate change in mineralogy. The low Curie point depth observed at the warm spring source is attributed to magmatic intrusions at depth. This is also evident from the visible older granite intrusion at Ikere - Ado-Ekiti area, with shallow Curie depths (12.37 ± 0.73 km). Results indicate that the area is promising for further geothermal explorations.

Modelling of magnetic data for scaling geology

ABSTRACTInterpretation of magnetic data can be carried out either in the space or frequency domain. The interpretation in the frequency domain is computationally convenient because convolution becomes multiplication. The frequency domain approach assumes that the magnetic sources distribution has a random and uncorrelated distribution. This approach is modified to include random and fractal distribution of sources on the basis of borehole data. The physical properties of the rocks exhibit scaling behaviour which can be defined as P(k) = Ak−β, where P(k) is the power spectrum as a function of wave number (k), and A and β are the constant and scaling exponent, respectively. A white noise distribution corresponds to β = 0. The high resolution methods of power spectral estimation e.g. maximum entropy method and multi‐taper method produce smooth spectra. Therefore, estimation of scaling exponents is more reliable. The values of β are found to be related to the lithology and heterogeneities in the crust. The modelling of magnetic data for scaling distribution of sources leads to an improved method of interpreting the magnetic data known as the scaling spectral method. The method has found applicability in estimating the basement depth, Curie depth and filtering of magnetic data.

Thermal evolution of the North Atlantic lithosphere: New constraints from magnetic anomaly inversion with a fractal magnetization model

Using recently published global magnetic models, we present the first independent constraint on North Atlantic geothermal state and mantle dynamics from magnetic anomaly inversion with a fractal magnetization model. Two theoretical models of radial amplitude spectrum of magnetic anomalies are found almost identical, and both are applicable to detecting Curie depths in using the centroid method based on spectral linearization at certain wave number bands. Theoretical and numerical studies confirm the robustness of this inversion scheme. A fractal exponent of 3.0 in the magnetic susceptibility is found suitable, and Curie depths are well constrained by their known depths near the mid‐Atlantic ridge. While generally increasing with growing ages, North Atlantic Curie depths show large oscillating and heterogeneous patterns related most likely to small‐scale sublithospheric convections, which are found to have an onset time around 40 Ma and a scale of about 500 km, and are in preferred transverse rolls. Hotspots in North Atlantic also contribute to large geothermal and Curie‐depth variations, but they appear to connect more closely to geochemical anomalies or small‐scale convection than to mantle plumes. Curie depths can be correlated to heat flow gridded in a constant 1° interval, which reveals decreasing effective thermal conductivity with depths within the magnetic layer. North Atlantic Curie points are mostly beneath the Moho, suggesting that the uppermost mantle is magnetized from serpentinization and induces long‐wavelength magnetic anomalies. Small‐scale convection and serpentinization together may cause apparent flattening and deviations in heat flow and bathymetry from theoretical cooling models in old oceanic lithosphere.

The Curie depth of Australia, and its uncertainty

The Curie depth is the depth at which the crust or upper mantle ceases being magnetic due to temperature effects. Although there are several methods available to map this depth, magnetic methods are most often used. These methods, however, introduce uncertainty into the depth estimates and have not been adequately addressed in previous studies. In this study, we have used magnetic data, at multiple scales, in combination with Monte Carlo techniques to evaluate both the Curie depth and its uncertainty for the Australian continent. Variations in the Curie depth for Australia is related to differences in mineralogy and thermal regimes across differing provinces of Australia, and may also be used to further our knowledge of crustal geothermal gradients. Increasing our knowledge in these areas will advance our understanding of uranium, geothermal and hydrocarbon systems in Australia.

Long-wavelength magnetic anomalies as a guide to the deep crustal composition and structure of eastern Australia

Aeromagnetic data over eastern Australia reveal a pattern of domains defined by systematic regional highs and lows, emphasised by low-pass filtering, over which are superimposed shorter (<20 km) wavelength anomalies related to mappable geology and its inferred subsurface continuation. Long-baseline levelling by Geoscience Australia has clarified the definition of these magnetic domains, and confirmed that they are not an artefact of grid merging. Geothermal and teleseismic data indicate that neither variation in Curie depth nor upper mantle magnetisation can produce the long-wavelength pattern. Hence, domain-wide variations in magnetisation at the middle to lower crustal level are presumably the cause of these long-wavelength features. Although reversed polarity remanence could contribute to deeply sourced negative magnetic anomalies, the correspondence of magnetic low domains with the Proterozoic Curnamona Craton and the Ordovician Macquarie Arc, and of a high domain with the western Lachlan Orogen floored by Cambrian ocean crust, suggests that the control may be simply stark contrasts in lower to middle crustal susceptibility. Moho thickness determined by the AusMoho model mimics the pattern of susceptibility domains, suggesting a relationship between tectonic history and mid to lower crustal composition. Implicit in this analysis is a division of the domains into continental and oceanic basement, with implications for the tectonic evolution of the Tasmanides and the distribution of mineral systems in eastern Australia. The mid to lower crust below the Macquarie Arc appears to be continental, and the Thomson Orogen is a compound feature, comprising both attenuated continental/arc crust and accreted oceanic crust.

Curie isotherm depth from aeromagnetic data constraining shallow heat source depths in the central Aeolian Ridge (Southern Tyrrhenian Sea, Italy)

The Salina, Lipari, and Vulcano volcanic ridge and the surrounding sea sectors (Aeolian Archipelago, Southern Tyrrhenian Sea, Italy) are characterized by vents responsible for a recent (<40 ka—1889/1890 AD) effusive and explosive subareal activity and repeated, 56 to 7 ka in age, submarine explosive eruptions from source areas located between Lipari and Vulcano. A spectral depth estimation of the magnetic bottom using a fractal method on aeromagnetic data from Vulcano, Lipari, and Salina volcanic ridge allows us to constrain the Curie isotherm depth. The elevated portion of the isotherm is between 2 and 3 km below Salina and Vulcano and about 1 km below Lipari. The Curie depth results in the context of other geological and geophysical evidence suggest that the rise of the Curie isotherm is mainly due to the occurrence of shallow heat sources such as magma ponds and associated hydrothermal systems. The short-wavelength magnetic anomaly field reflects magnetic contrasts from highly magnetized volcanic bodies, low-magnetization sediments, and hydrothermally altered rocks. Borehole temperature data verify the Curie temperature derived from the magnetic methods on the island of Vulcano. We conclude that the whole Vulcano, Lipari, and Salina volcanic ridge is active and should be monitored.

Application of spectral analysis technique on ground magnetic data to calculate the Curie depth point of the eastern shore of the Gulf of Suez, Egypt

The bottom of the magnetized crust determined from the spectral analysis of magnetic anomaly is interpreted as a level of the Curie point isotherm. A spectral analysis technique was used to estimate the depth of the magnetic anomalies sources (Curie point depth analysis) of the eastern shore of the Gulf of Suez, Egypt. The depth to the tops and centers of the magnetic anomalies are calculated by azimuthally averaged power spectrum method for the whole area. The results obtained suggests from this study showed that the average depth to the top of the crustal block ranges between 1.15 and 1.9 km, whereas the average depth to the center of the deepest crustal block ranges between 9.1 and 12.7 km. Curie point depths in the study area range between 14.5 km in the northwestern part of the study area and 26 km in the southeastern part of the study area. The results imply a high geothermal gradient (34.7 °C/km) and corresponding high heat flow value (72.87 mW/m2) in the northwestern part of the study area. The southeastern part of the study area displays a low geothermal gradient (24.26 °C/km) and low heat flow value (50.9 mW/m2). These results are consistent with the existence of the possible promising geothermal reservoir in the eastern shore of the Gulf of Suez especially at Hammam Faraun area.