Spectral Analysis Of Magnetic Data Research Articles

Curie Point Depth from Spectral Analysis of Magnetic Data in Potiskum and Environs, Yobe State, Nigeria

The area under investigation, is part of Chad basin of northeastern Nigeria, located between latitudes 11o00´ to 12o00´N and Longitudes 11o30´ to 12o30´E, with the objective to discover more about the thermal structure of the crust in the area, a research was carried out over Potiskum and surrounding regions in Yobe State, Nigeria to estimate the curie point depth, geothermal gradient, and heat flow using spectrum analysis and empirical formula of aeromagnetic data. To acquire the regional and residual data, polynomial fitting was applied to the high-resolution digital aeromagnetic data. In order to calculate the depth to the centroid and the depth to the top boundary, the upward continued residual data was processed to produce the upward continued data, that was subjected to spectral analysis. The depth to the centroid is between 10.50 and 11.50 kilometers, the depth to the top boundary is between 5.90 and 7.16 kilometers, the depth to the Curie point is between 14.84 and 16.83 kilometers, the geothermal gradient is between 34.462 and 39.083 oCkm-1, and the heat flow is between 86.135 and 97.707 mWm-2. The Curie point depth inferred from the study indicates that the crust is thinning due to thermal upwhirling of magma and is moderately decreasing toward areas of volcanic activity that occurred in the area during the Tertiary Period. The Geothermal gradient shows that the area is a moderate temperature zone, which could likely result in partial thermal maturation of sediments and hence probable oil generation as time goes on with an increase in temperature. In the research area, the geothermal gradient is proportional to the heat flow, whereas the connection between curie depth and heat flow is inversely linear. These findings are in line with the geotectonic regime that is now in effect in the research area. However, this analysis shows that the heat flow that was obtained from the study is sufficient to be utilized as a geothermal energy source.

A review of spectral analysis of magnetic data for depth estimation

Spectral analysis has been used for studying a variety of geologic structures and processes, such as estimation of the depth to the crystalline basement or estimation of the Curie temperature isotherm from magnetic anomalies. However, the analysis is not standard because it refers to different theoretical frameworks, such as statistical ensembles of homogeneous sources and uncorrelated or fractal randomly distributed sources. We have aimed to unify the approaches by reformulating all of the common spectral expressions in the form of a product between a depth-dependent exponential factor and a factor, which we call the spectral correction factor, that incorporates all of the a priori assumptions for each method. This type of organization might be useful for practitioners to quickly select the most appropriate method for a given study area. We also establish a new formula for extending the Spector and Grant method to the centroid depth estimation. Practical constraints on the depth estimation and intrinsic assumptions/limitations of the different approaches are examined by generating synthetic data of homogeneous ensemble sources as well as random and fractal models. We address the statistical uncertainty of depth estimates using ordinary error propagation on the spectral slope. Critical parameters, such as the window size, are also analyzed in terms of the type of method used and the geologic complexity. We find that the window size is smaller for the centroid/modified centroid methods and larger for the spectral peak, defractal, and nonlinear parameter depth estimation methods. In any case, the window size can be large in tectonically stable regions and relatively small over volcanically, tectonically, and geothermally active areas. Finally, we estimate and discuss the depth to the magnetic top and bottom in the Adriatic Sea region (eastern Italy) in the context of the heat flow, Moho depth, and gravity data of the region.

Correction to: Geothermal Prospectivity of the Bigadic Basin and Surrounding Area, NW Anatolia, Turkey, by the Spectral Analysis of Magnetic Data

The Curie Point Depths (CPDs) are estimated from the spectral analysis of magnetic data in order to determine the geothermal potential of the Bigadic Basin and its surrounding region in NW Anatolia, Turkey. The estimated CPD range is from 7 to 17–18 km. The shallowest depth (7 km) lies to the north of Balikesir. The estimated geothermal gradient and heat flow values range from 33 to 80 °C/km, and 83 to 200 mWm−2, respectively. All results in the study area support the previous studies from the geological or geophysical investigations for western Anatolia by other researchers. High temperatures may be resulted indirectly from the continental collision and consequent thermal relaxation and/or heating from the interiors of the Earth due to the mantle delamination or asthenospheric upwelling in response to lithospheric extension in the western Anatolia. The high heat flow and shallow CPDs can also be associated with the magmatic rocks as a consequence of the recent tectonic extension and granitoids in the studied region.

Geothermal Prospectivity of the Bigadic Basin and Surrounding Area, NW Anatolia, Turkey, by the Spectral Analysis of Magnetic Data

Geothermal Prospectivity of the Bigadic Basin and Surrounding Area, NW Anatolia, Turkey, by the Spectral Analysis of Magnetic Data

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

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

Spectral Analysis of Magnetic data in the Ajmer-Sambar Sector, North-Central Rajasthan

Ajmer-Sambar sector of Delhi fold belt, North-Central Rajasthan has got importance due to its litho characters, structure, metamorphism, magmatism, migmatisation, metallogeny and rich potential of base metal mineralization. This sector is comprised of Delhi sequence of rocks hosted by the Banded Gneisses Complex (BGC). In view of the significance of this region, ground magnetic survey was conducted along six regional profiles to understand the structural features, magnetic nature of the basement and depth to the basement. Analysis of the magnetic data has clearly identified two magnetic lineaments (a) L1 in WNW-ESE direction that appears to represent litho-contact between Kalyanpura sequences in the south to Anasagar migmatite in the north and (b) L2 in NNW to SSE direction south of Parvatsar which is inferred to be a structural control about which the quartzite rocks of Taragarh Formation culminate. An average depth to basement of 3.7 km is estimated through spectral analysis of magnetic data. The maximum depth of the basin 4.5 km is estimated in central part of the study area. The obtained depth results are in good agreement with the Cummulative Total Intensity Magnetic Anomaly field (CTIMAF) and Deep seismic stuides.

Curie Point Depth from Spectral Analysis of Magnetic Data in the Southeast Tibet

The satellite magnetic anomalies are used to calculate the Curie point depth of the Southeast Tibet by spectral analysis method in the study. The relationship between the Curie point depth and the regional faults or heat flow will be discussed. The results show that the Curie point depth of the study area ranges from 15 km to 36 km and the average depth is 26.3 km. The Curie point depth is cluster-like on the north of the Ailaoshan-Red River Fault, while it is strip-like distribution on the north side. The Curie point depth in the Xiaojiang Fault zone, the Xiaojinhe Fault zone, the Dien Bien Phu Fault zone and the Gaoligong Fault zone are shallow. It could be related to their strong frictional heat induced by these faults. The Curie point depth in the middle Sukhothai Block is shallow, which it is not only related to the Phayao Fault, the Mae Chan Fault and the Nam Ma Fault, but also to the subduction of the Palaeo-Tethys into the Indochina Block. There is a negative but nonlinearly correlation between the heat flow and the Curie point depth in this study area. The areas of low heat flow value correspond to the areas of deep Curie point depth. However, both the high and low heat flow values can be found in the areas of shallow Curie point depth. The possible reason is thought to be related to the low thermal conductivity of the rock.

Interpretation of aeromagnetic data over Abeokuta and its environs, Southwest Nigeria, using spectral analysis (Fourier transform technique)

Abstract This study presents the results of spectral analysis of magnetic data over Abeokuta area, Southwestern Nigeria, using fast Fourier transform (FFT) in Microsoft Excel. The study deals with the quantitative interpretation of airborne magnetic data (Sheet No. 260), which was conducted by the Nigerian Geological Survey Agency in 2009. In order to minimise aliasing error, the aeromagnetic data was gridded at spacing of 1 km. Spectral analysis technique was used to estimate the magnetic basement depth distributed at two levels. The result of the interpretation shows that the magnetic sources are mainly distributed at two levels. The shallow sources (minimum depth) range in depth from 0.103 to 0.278 km below ground level and are inferred to be due to intrusions within the region. The deeper sources (maximum depth) range in depth from 2.739 to 3.325 km below ground and are attributed to the underlying basement.

Craton vs. rift uppermost mantle contributions to magnetic anomalies in the United States interior

article i nfo The interpretation of satellite magneticinformation (Magsat,Oersted, CHAMP, Swarm)requirestheunderstand- ing of the mineralogy of crustal and mantle sources. Also, spectral analysis of magnetic data over forearcs and cratons calls for upper mantle contribution. The prospect of such a contribution contradicts the view that the mantle is too hot and its magnetism is too weak to influence magnetic anomalies. Here we examine the rock magnetic properties of fresh mantle xenoliths from four settings across the United States: phlogopite-spinel dunites from the Bearpaw Mountains, Montana, and lherzolites/harzburgites from San Carlos, Arizona; Kilbourne Hole, New Mexico; and Knippa, Texas. Paleomagnetic results show single- component natural remanent magnetizations (NRMs), which, combined with optical and secondary electron microscopy support the lack of post-eruption alteration and absence of host-rock contamination. The NRM carriers include magnetite at Bearpaw Mountain and San Carlos, and pyrrhotite at Kilbourne Hole and Knippa. These four areas show continental crust of distinct thicknesses and various geotherms. The potential mantle contribution to magnetic anomalies is forward modeled using crustal thickness, current geotherm and average magnetic properties of xenoliths. The San Carlos and Kilbourne Hole mantle, situated near the Rio Grande Rift istoohotandits magnetism istooweaktocontribute toanomalies.The sulfide-dominatedassemblageatKnippa does not support magnetization at mantle depths. In contrast, the Bearpaw Mountains combine a relatively cold geotherm(craton) andabundanceof magnetite formedatmantledepth.Thiscratonicmantle,metasomatizedby fluids from the Farallon plate, may contribute to long wavelength magnetic anomalies.

Curie point depth from spectral analysis of magnetic data in Taiwan

This study constructs an integrated magnetic anomaly map of Taiwan and its vicinity that combines land magnetic data and marine magnetic data. The reduction to pole (RTP) correction method was applied to the integrated magnetic anomaly data. The corrected magnetic anomaly results for a region roughly 880km in width and 660km in length fit well with geological tectonic signatures and are used to estimate the Curie point isotherm. The adopted Curie point depth method provides a relationship between the 2-D FFT power spectrum of the magnetic anomalies and the depth of magnetic sources by transforming the spatial data into the frequency domain. The basal depth of the magnetic sources is calculated from the magnetic data. Finally, the Curie point depth of Taiwan is obtained. The highest value of 17km is located in northern Taiwan, and the lowest value of 6km is located at southern Taiwan and also has the highest thermal gradient of 88°C/km. The Curie point depth is consistent with heat-flow measurements with correlation coefficient 0.62.

Curie-point Depth from Spectral Analysis of Magnetic Data in Erciyes Stratovolcano (Central TURKEY)

Curie-point depth and heat flow values of the Erciyes region are determined to identify the thermal regime of the Central Anatolia by applying the spectral analysis method to the magnetic anomaly data. To compute the spectrum of the data, the magnetic anomaly of the region is transformed into 2-D Fourier domain to attain the average Curie depth. This method is useful in determining the top boundary of magnetic anomaly sources and reveals the Curie depth as 13.7 km in the study area. The obtained results imply a high thermal gradient (42.3°C km−1) and corresponding heat flow values (88.8 mWm−2) in the research area. Using the temperature value measured at borehole drilled by the General Directorate of Mineral Research and Exploration of Turkey (MTA), the values for the thermal gradient and heat flow value were computed as 50.7°C km−1, 106.5 mWm−2. From the heat flow value, the Curie-point depth was determined as 11.4 km in this region. It is concluded from the obtained values that the region has very high geothermal potential caused by partial melting of the lower crust.

Crustal Thermal Properties of the Central Pontides (Northern Turkey) Deduced from Spectral Analysis of Magnetic Data

The Pontides can be divided tectonically into three main sectors: Eastern, Central, and Western Pontides. Each of these represents an amalgamated tectonic mosaic consisting of remnants of oceanic, continental, and island arc segments. The Eastern and the Western Pontides meet in the Central Pontides, where they are structurally mixed and form a tectonic knot. The Central Pontides of northern Turkey is one of the best exposed segments of the southern margin of Eurasia adjacent to the Tethys Ocean. The study area also extends to parts of the Sakarya and Kırşehir continents. Magnetic spectral analysis, which has been used to estimate the Curie point depths and heat flow values, is employed to identify the thermal regime of the Central Pontides. The magnetic data of the region are separated into five subregions and the power spectra of each region is achieved by using 2D Fourier transform method to attain the average curie depth. The curie depth values changes across the studied region from 14.8 km in the south to 21.8 km in the north. The obtained results imply a high thermal gradient (39.2 °Ckm^{-1}) and corresponding heat flow values (94.1 mWm^{-2}) in the south of the research area. The northern part of the study area displays a low thermal gradient (26.6 °Ckm^{-1}) and low heat flow value (63.9 mWm^{-2}), corresponding to the Central Pontides consisting of accreted oceanic crustal material. The determined values show the heat flow decrease within the accretionary prism toward the island arc-like Pontides.

Curie-point depth from spectral analysis of magnetic data in central–southern Europe

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).

Inherent limitations in the determination of basalt flow thickness using magnetic spectral techniques

The method for the location of deposits of heavy minerals such as gold and tin, which occur in deep leads overlaid with volcanic lava flow, is a problem whose solution is of significant economic importance. For this reason it has been the subject of geophysical research for many years. Of the numerous methods investigated, spectral analysis of magnetic data in particular has been developed over the past quarter of a century, and success has been reported in the determination of the average depth to magnetic interfaces using aeromagnetic data and the spectral slope method.