Reduction To The Pole Research Articles

Estimation of Subsurface Structure Using Euler Deconvolution Method of Magnetic Data at the Geothermal Area of Sonai Village and its Surroundings, Konawe Regency

It has been carried out research with the aim of determining the subsurface structure at the geothermal area of Sonai Village and its surroundings, Konawe Regency. The data used are magnetic data obtained through field measurements at 126 points in the N180oS direction. After the data were subjected to diurnal and IGRF corrections, a residual (local) magnetic field anomaly of around -150 nT to 90 nT was obtained. On the residual magnetic anomaly map which has been reduced to the Pole (RTP), the Euler Deconvolution (ED) method is applied to the Index Structure N=0 to estimate the subsurface structure in the form of the presence of minor faults, and it is known that there are 5 minor faults at a depth of around 9 to 38 meters. Information on the existence of these faults is then used in 2D modeling. Modeling results show that these minor faults cut through two rock layers, which are the layers composed of conglomerate rocks from the Alangga Formation and peridotites as bedrock from the Ultramafic Complex. One of the minor faults closest to the manifestation area (hot spring) is at coordinates around 4o1’12.412” S and 122o7’24.263” E to 4o1’15.532” S and 122o7’19.561” E with a distance of ±15 meters. The existence of these minor faults is thought to be the migration routes for heat flow or conduction to the surface at the geothermal area of Sonai Village and its surroundings.

Litho-structural interpretation of aeromagnetic anomalies reveals potential for mineral exploration in Tizi n'Test Region, Western High Atlas, Morocco

This study interprets aeromagnetic data from the Tizi n'Test area in the High Atlas massif of Morocco, aiming to gain insights into its litho-structural architecture and implications for mineral exploration and mining. We employed six different analytical techniques to the residual magnetic field data, including reduction to the pole (RTP), upward continuation, total horizontal derivative, Tilt angle, Centre for Exploration Targeting (CET) analysis, and Euler deconvolution. Our analyses differentiated the study area into three magnetic domains: the eastern Ouzellarh block, characterized by positive anomalies, a central domain characterized by a negative magnetic signature demarcating the transitional zone between the Anti-Atlas and the High Atlas separated by the Ouchden fault: and the western domain, represented by the Tichka massif. The application of total horizontal derivative, tilt angle, and a combination of filters in ternary image formats (Tilt angle, upward continuation 1000 + Tilt angle and upward continuation 3000 + Tilt angle) revealed both known and previously unidentified geological lineaments, mapping structural complexity across various orientations (NE–SW, NNE–SSE, E–W, NW–SE, and N–S). The CET grid analysis method unveiled the structural complexity, highlighting the geodynamic evolution of the region. Particularly, the Ouchden fault delineates a magnetic domain divide between the ancient High Atlas and the Ouzellarh block (Anti-Atlas). Furthermore, Euler deconvolution indicated magnetic source depths ranging from 52 m in the western domain of the Tichka massif to 6560 m in the Ouzellarh block. A comprehensive structural scheme, classified by C-A fractal analysis, identified zones favourable for exploration and mining, particularly along the Ouchden fault, Tizi n'Test, NE-SW trending lineaments in the northwestern domain, as well as along the Tichka granite’s margin.

Characterization of Mineral Meposits Using the Magnetic Method: The Case of the Aïn Beida Mine in Bouarfa, Morocco

Abstract Geophysical methodologies represent a paramount approach for assessing the mining potential of a given area. Among these methodologies, the magnetic method stands out as indispensable for the exploration of metalliferous deposits. This method facilitates the characterization of both the lateral extent and vertical depth of anomalous bodies within the surveyed region, as discerned from their influence on the total magnetic field. In the case of the manganese-rich mining zone situated in Bouarfa, particularly in Aïn Beida, the mineral deposit genesis typically involves the association of manganese with ferruginous minerals, significantly perturbing the total magnetic field. However, the initial findings necessitate meticulous corrections to isolate the exclusive impact of anomalous bodies on the magnetic field. Accordingly, correction procedures must address diurnal variations prior to executing a Reduction to the Pole (RTP), enabling the identification of well-defined and unipolar anomalies crucial for precise delineation of potentially mineralized zones. Integration of spatially interpolated data yields comprehensive maps delineating areas of mining significance and elucidating pertinent geological phenomena within the study area. Subsequently, employing 2D modeling techniques on magnetic survey results facilitates accurate estimation of mineralized horizon extents and thicknesses. Ultimately, these synthesized maps serve as valuable guides for subsequent mechanical prospecting endeavors aimed at corroborating findings derived from geophysical methodologies.

Reduction to the pole near the equator with a Fourier-domain equivalent dipole layer

Reduction to the pole (RTP) transforms the phase of the observed total-field anomaly, making magnetic interpretation easier. However, RTP operations are notoriously unstable at low latitudes and produce singularities at the equator. The equivalent-source approach is an appropriate method to address the well-known difficulties of RTP at low latitudes. Although we routinely use equivalent-source RTP algorithms in the spatial domain, they consume massive computational resources. In contrast, the equivalent-source method in the Fourier domain is more efficient and also invalid for RTP because of the inevitable use of the RTP operator in the inversion. To overcome this problem, we introduce a simple approximation of the RTP operator instead and then develop a novel algorithm to calculate the magnetic moments of the equivalent dipole layer from the total-field anomaly near the equator. Because the calculations are mainly performed in the Fourier domain, this algorithm is more efficient than the conventional spatial-domain method. We also impose a nonnegative constraint on the dipole layer to improve the results and significantly reduce the undesired striation associated with the low-latitude RTP. We evaluate the effectiveness of our approach with synthetic data near the equator, and the results indicate that the algorithm can produce an RTP field that is an accurate representation of the real field at the pole, even when accounting for the existence of noise. The new approach is applied to field data collected near the geomagnetic equator in the South China Sea. In the central part of the anomaly, we obtain a robust spindle shape of the RTP field, which is identical to the shape of a basalt formation in that location. Recent 1:1,000,000 scale marine geologic mapping has confirmed this presence, proving that our solution is an applicable approach to the problem.

Study on the Significance of Reduction to the Equator (RTE), Reduction to the Pole (RTP), and Pseudogravity in Magnetic Data Interpretation

Interpretation of geomagnetic anomaly data is challenging, due to the influence of the Earth's dipole magnetic field. In this study, we investigate the significance of employing methods to transform dipole anomalies into monopoles, aiming to enhance the interpretability of the data. Four methods were examined: Reduce to Pole (RTP), Reduce to Equator (RTE), and Pseudo-Gravity. The RTP method was implemented using general equations for RTP, Pseudo-inclination (PI), and Nonlinear thresholding (NTRTP). The computation programs for RTP and RTE were developed using the Matlab programming language. Synthetic models were constructed to investigate the effects of inclination values, object dimensions, and positions on the resulting magnetic anomaly response. The result shows that NTRTP methods give the best result with coefficient correlation >0.9. It can be used in every condition (low or high inclination). The implementation was conducted utilizing magnetic data in the Gunung Pandan geothermal area. The application of the reduced to the pole (RTP) technique on the field data successfully remove the dipole effects, and make interpretation process easier. Based on RTP map, the range of anomaly values spanning from -800 nT to 1000 nT. High anomalies were observed at the Gunung Pandan site, indicative of a probable intrusion of andesitic igneous rock.

Geological Structures Controlling Au/Ba Mineralization from Aeromagnetic Data: Harrat ad Danun Area, Saudi Arabia

Positive and negative magnetic anomalies occupied the total aeromagnetic (TM) map of the Harrat ad Danun area, Saudi Arabia. Reduction to the pole (RTP) maps display the range of magnetic values (−312.4 to 209.4 nT) that vary in shape, size, and magnitude. These anomalies generally follow the NNW–SSE (Red Sea axis trend), NE–SW, and NNE–SSW trends. The NNW-SSE linear negative and positive magnetic anomalies could be brought on by buried faults, shear zones, or subsurface dikes. In the central part, the position of Au and Ba mineralization was connected to this trend. It is concluded that the principal structures are represented by the NNW–SSE, NE–SW, and NNE–SSW tendencies. Based on gridded RTP magnetic data, the 2-D power spectrum was computed and revealed the frequency of the near-surface and deep magnetic components. It is believed that the depths of the shallow and deep magnetic sources are typically 80 m and 570 m, respectively. Additional negative and positive magnetic anomalies with varied amplitudes and frequencies, trending in the NNW–SSE, ENE–WSW, and NE–SW directions, are seen when the high-pass and low-pass maps are closely examined. Many faults in various directions cut into these anomalies. The occurrence of negative linear magnetic anomalies (−36.6 nT to −137.3 nT) at this depth (80 m) is also confirmed by this map. The TDR filter and the Euler deconvolution method were used to identify the horizontal variations in magnetic susceptibility as well as the source position and depth of magnetic sources. The linear clustering rings are thought to be caused by contacts or faults with depths between 1 m to 474 m that are oriented WNW–ESE, NNE–SSW, and NNW–SSE. These faults or contacts are thought to be particularly prominent in the western, eastern, southern, northern, and central zones. The majority of felsic and mafic dikes are found to be connected to subsurface structures, showing that three structural trends—WNW–ESE, NNE–SSW, and NNW–SSE—affect the studied area. This demonstrates that important features and shear zones control the majority of Saudi Arabia’s gold deposits. A negative magnetic anomaly that is centered in the area, trending NNW–SSE and crossing the NNE–SSW fault, is connected to the plotted gold and barite mineralization in the study area. This may imply that these two tendencies are responsible for mineralization. This result raises the possibility of mineralization in the NNW negative magnetic feature located in the western part of the area. The occurrence of gold and barite was significantly impacted by the NNW–SSE and NNE–SSW structural lineaments.

Integrated Identification of Lithology Using Seismic and Magnetic Anomaly Data for Granite and Gneiss Basement: A Case Study of the LiShui Depression in the East China Sea Basin

Granite and gneiss buried hill reservoirs are controlled by their lithology and dark mineral content. Therefore, lithological identification and dark mineral content analysis are important research tools in the early stage of buried hill exploration. In this paper, the relationships between the seismic facies and lithology, magnetic susceptibility, and magnetic anomalies of granite and gneiss are analyzed based on the lithological characteristics of the LiShui depression (LS depression) in the East China Sea Basin (ECSB). The waveform classification method is used to identify granite and gneiss, and the waveform classification results reveal that areas with continuous distribution of a single seismic trace model or two seismic trace models represent good continuity, and can be interpreted as gneiss. Areas with a mixed distribution of multiple seismic trace models represent chaotic and poor continuity, which can be interpreted as granite. The mixed linear zone with multi-seismic trace models is a fault zone, and the rock is cataclasite. In addition, reduction to the pole (RTP) and downward continuation technique for magnetic data processing were used to determine the dark mineral content. Overall, the granite and gneiss can be divided into three types based on magnetic anomaly data: high, moderate, and low magnetic anomaly areas. The areas in which granite with moderate and low magnetic anomalies is distributed are the favorable exploration target areas. The above method provides a technical means of lithological identification in the early stage of buried hill exploration.

TWO-DIMENSIONAL MODELING OF MAGNETIC ANOMALY DATA REDUCED TO THE POLES IN THE ANDESITIC PROSPECT AREA OF THE SOUTHEAST SLOPE OF SLAMET VOLCANO, INDONESIA

Reduction to the pole (RTP) is a magnetic anomaly data processing filter to remove the influence of the magnetic inclination angle. This filter is needed because of the magnetic dipole nature which complicates the interpretation process. The research aims to explore andesite rocks through the application of RTP to the local magnetic anomalies data in Kutasari District, Purbalingga Regency, Indonesia. The research procedures include data acquisition, processing, modeling, and interpretation. The 2D-modeling results on the local magnetic anomalies data have produced three layers of rock. Layer with a susceptibility value of 0.00291 cgs is interpreted as vesicular andesitic rocks, layer with a susceptibility value of 0.02307 cgs is interpreted as massive andesitic rocks, meanwhile layer with a susceptibility value of 0.00721 cgs is interpreted as undifferentiated volcanic rocks. The results showed that the west to northwest part of the study area is the most prospective area containing andesite rocks.

Improved MAX-MIN method to estimate total magnetization direction using Wiener filtering

Knowledge of the total magnetization direction is useful for forward modeling and reduction-to-the-pole (RTP) of magnetic anomalies. However, remanent magnetization deviates the total magnetization direction from the induced magnetization direction; therefore, it is essential to determine the correct direction of total magnetization. Theoretically, the MAX-MIN method, which searches for the position of the maximum value of the function that comprises the minimum values of the RTP field with different directions, can yield the correct direction of total magnetization. However, such estimations of direction usually indicate large errors in comparison with the results of crosscorrelation methods, which calculate the correlation coefficient between the RTP field and the magnetic magnitude transforms. Our analysis reveals that noise is the primary cause of the inaccuracy in estimation results. We have improved the MAX-MIN method using Wiener filtering based on the principle of least-mean-squares deviation. The k-means clustering algorithm clusters points that are as closely connected as possible, while ensuring that the distances between clusters are as large as possible. Therefore, the k-means clustering algorithm is used to divide the radial logarithmic power spectrum into the effective signal with low wavenumbers and the noisy signal with high wavenumbers. Then, the Wiener filtering RTP operator is constructed using the slope and intercept of the fitted straight line in the corresponding wavenumber bands. The improved MAX-MIN method is tested using magnetic anomalies of spherical and combined cuboid models with different levels of added Gaussian noise and different total magnetization directions. The improved MAX-MIN method is applied to the magnetic anomaly in the Yeshan region (eastern China) and the Taihe region (southwestern China). Results indicate that the improved MAX-MIN method based on the principle of least-mean-squares deviation could obtain reliable estimation of direction from noisy magnetic anomaly data.

Gravity and magnetic field features and the prospects of iron deposits in the eastern Hebei province, China

To study the features of the gravity and magnetic anomalies and the prospects of iron deposits in the eastern Hebei province, we have collected and arranged gravity data at scales of 1:50,000 and 1:200,000 and aeromagnetic data at scales of 1:25,000 and 1:200,000. Then, we have separated the Bouguer gravity anomaly and the aeromagnetic anomaly by reduction to the pole (RTP) by the moving average method and processed these two anomalies using the total horizontal gradient method and the vertical second derivative method. Combined with existing geologic and geophysical research, we have studied the features of the gravity and magnetic anomalies and investigated the corresponding relationship between the distribution of iron deposits and these anomalies, and then we predicted the favorable areas for iron deposits in the eastern Hebei province. The results find that there is a good corresponding relationship between the distribution of iron deposits and the gravity and magnetic anomalies in the eastern Hebei province. Identification marks of the gravity and magnetic anomalies are determined to find the iron deposits in the eastern Hebei province, including the magnetic highs of the local magnetic anomaly and the vertical second derivative anomaly, the gravity highs of the local gravity anomaly and the vertical second derivative anomaly, the gradient belts of the Bouguer gravity anomaly, the high-value zones of the RTP aeromagnetic anomaly, and the extreme-value zones of the total horizontal gradient of the Bouguer gravity anomaly and the RTP aeromagnetic anomaly. There are 17 favorable areas for iron deposits in the eastern Hebei province, and these favorable areas display complex trends, including east–west-trending, north-northwest-trending, and northeast-east-trending features.

A new method to estimate the total magnetization direction from the magnetic anomaly: Multiple correlation

Natural remanent magnetization diverts the direction of the total magnetization vector from the earth’s magnetic field direction. It is important to determine the magnetization direction because the processing and inversion of magnetic usually need the magnetization direction as a priori information. The conventional strategy for estimating the magnetization direction is to compute the crosscorrelation between the reduced-to-the-pole (RTP) field and one magnetic magnitude transform, which is insensitive to the magnetization direction. A new theory and method are proposed that the total magnetization direction is determined by computing the multiple correlation coefficients between the RTP field and the multiple direction-insensitive magnitudes transforms, such as the total magnitude anomaly and the normalized source strength. The linear regression between the RTP field and the direction-insensitive magnitude transforms is established. Then, the correlation is computed by the RTP field and the constructed regressor. The proposed method is tested on synthetic of single and complex models, respectively. Then, the method is applied to the field data of the Yeshan region (eastern China) and the Black Hill Norite (southern Australia). The proposed multiple correlation is an extension of the conventional crosscorrelation method that provides an accurate and robust way to estimate the magnetization direction from the total field anomaly.

Interpretation of the magnetic anomalies over the Mid-Atlantic Ocean Ridge using Swarm-A satellite

The procedures and interpretation of the magnetic data measured over the Mid-Atlantic Ocean Ridge by Swarm-A satellite is discussed in this paper. The data processing procedure has four phases after the data format conversion. The first phase is the selecting data whose Kp index is lower than 1. Secondly, the main magnetic field should be subtracted from the measured data for example through the IGRF model. This step is followed by removing trend, related to the satellite trajectory. The final step is eliminating the dipole nature of the magnetic field via Reduction to the Pole (RTP). Nonetheless, the RTP process might cause misinterpretation over the large study area and lower latitudes. Therefore, the amplitude of the analytic signal (AS) is used as an alternative to the RTP. The qualitative interpretation of the magnetic anomaly is conducted via AS anomaly, bathymetry, heat flow and tectonic map. Quantitatively correlation coefficients of bathymetry and heat flow with respect to AS are interpreted.

Comparative study of estimating the Curie point depth and heat flow using potential magnetic data

Abstract The estimation of the Curie point depth (CPD) and heat flow (HF) from magnetic data is useful for geothermal and tectonic studies. However, the methodology of estimating these values is still controversial as numerous studies have used different types of transformed magnetic data. Most studies utilize the total magnetic intensity (TMI) or the reduced to the pole (RTP) data, and since shallow magnetic bodies may affect the final CPD values, low-pass (LP) wavelength filtering has also been used to estimate the CPD. In this study, the two-dimensional radially averaged spectral analysis was applied to the land-based magnetic data from the Sinai Peninsula. TMI and RTP data were both analyzed, using different LP filtered wavelengths, and the final CPD and HF values were compared. The cut-off wavelength parameter was selected in terms of the geologic complexity. The results show that the estimated CPD values are well correlated regardless of whether the magnetic data were either TMI or RTP. The RTP data produced a spatial shift in the CPD smaller than the window size being used. Additionally, the centroid method is primarily dependent on the wavenumber, which varied slightly on applying the RTP. There were slight differences in the estimated CPDs when a short LP filter (e.g., 20 km) was applied, whereas increasing the wavelength (e.g., 40 km) caused the CPD values to increase exceeding the plausible depth limits, and the associated spatial trends varied when compared to the other methods. In areas where the basement rocks were shallow or exposed, a LP filter can be applied with short cut-off wavelength. The estimated CPDs were discussed in the context of seismicity data, gravity-based Moho depths, and HF measurements.

Crustal thickness and structural pattern evaluation of Sinai Peninsula using three-dimensional density modeling with aeromagnetic and earthquake data

The Sinai Peninsula is a subplate located between the African and Arabian plates. It is an important subplate in the world; however, this region is poorly understood because of the shortage of geophysical data. Thus, this study focuses on built a three-dimensional (3D) high-resolution forward model of the crustal thickness with a new tectonic model and structural evaluation of the Sinai Peninsula to understand this area tectonically and determine its lithospheric and crustal thicknesses. Qualitative and quantitative interpretations of Bouguer gravity, reduced-to-the-pole (RTP) aeromagnetic, and earthquake data are explained to achieve the goals of this study. Two-dimensional (2D) interactive sequential modeling of gravity data is performed along with some well-selected profiles with existing crustal layer depth points from previous works in the studied region. Seventeen 2D models are constructed and used to determine the basement, Conrad (lower crust boundary), and Moho (upper mantle boundary) depths and to build a 3D model. Accuracy of the 3D built model is evaluated by extracting observed, calculated, and residual gravity anomaly maps. The results show that the basement rocks appear on the surface in the South of Sinai and deepen (down to 4.5 km) toward the North. The Conrad surface varies approximately from 16 km (in the northeast and southwest of Sinai) to 22.8 km (in the southeast). The Moho surface depth (i.e., crustal thickness) varies approximately from 28.8 to 34.2 km, and it deepens toward the northeastern and southwestern parts of Sinai. A tentative basement structure map is constructed from the horizontal gradient (H-gradient) filter and the 3D Euler deconvolution of the Bouguer gravity and RTP aeromagnetic data. Correlation between the geological background of the study area and the obtained results suggests that the Sinai Peninsula is tectonically active, mainly in its southern portion due to the tectonic movements along the Gulf of Suez and the Gulf of Aqaba. The crustal thickness increases southward and thins northward.

Magnetic Structure and its Tectonic Implication Around Longmenshan Fault Zone Revealed by EMAG2v3

The formation of magnetic minerals is bound up with the tectonic evolution history, whereupon the distribution of magnetic anomalies has great meanings for regional tectonics. In this study, we use the latest global lithospheric magnetic field model EMAG2-v3, processed by various techniques including reduction to the pole (RTP), upward continuation, derivations, Euler deconvolution, estimation of total magnetization direction, and Curie point depth (CPD), to unveil the tectonics around Longmenshan fault zone (LFZ). LFZ is clearly displayed as a positive and negative anomaly transition zone in RTP anomalies and acts as a magnetic basement boundary. The Sichuan Basin (SB), located to the east of LFZ, is marked by strong magnetic basement and NE-strike banded induced positive anomalies which are associated with the Neoproterozoic magmatic activity. The banded shape, absence of radial pattern of anomalies, and existence of fossil subduction zone supports that the magnetic basement was formed in arc environment. The CPD in SB estimated by radial average power spectral is 30–51 km, which allows magnetic minerals in deep crust or even in lithospheric mantle to exhibit high magnetizations. The Songpan-Ganzi fold belt (SGFB), in contrast, is located to the west of LFZ and covered by thick and low-susceptibility Triassic deposits of flysch, manifests as weak negative anomalies caused by relatively shallow CPD and widespread remanent magnetization. Significant positive anomalies, appearing around the Manai and Rilonguan granitic massifs, indicate a strong magnetic basement beneath SGFB, which is conjectured as westward extension of the Yangtze Block at depth.

An integrated remote sensing, aeromagnetic and field study of the Ablah shear zone (Asir Terrane, Saudi Arabia): Structural styles and implications for the tectonic evolution

• Surface and subsurface structural mapping was carried out for the Ablah shear zone. • Northerly striking thrust faults define the positive flower structure that impacts the shallow rocks in the zone. • Shallow thrusting ends at 1.5 to 2 km depth and is converted into single thrust shear. • Contraction tectonic regime initiated the shear zone and was later superposed by dextral-transpression regime. An integration of merged remote-sensing data having different spatial/spectral resolutions with aeromagnetic data and detailed field investigation is used to identify the composite Neoproterozoic rock complexes and define the structural architecture of the Ablah Shear Zone (ASZ). The SPOT and Landsat-8 data are processed as color composite images allowed the separation of different lithologic units and associated structures. Aeromagnetic data were analyzed using the Total Magnetic Intensity (TMI) and Reduced to the Pole (RTP) methods. The resulted anomalies show seven N-S opposite-dipping thrust faults that affect the shallow crustal rocks and coalesce together at about 1.5 to 2 km depth where the rock magnetic polarities inversed. This thin-skinned thrusting was initiated by a contractional tectonic regime in the E-W direction and superposed later by a transpresssion tectonic regime in the ENE-WSW direction. This study deals with the thin-skinned thrusting deformation in the ASZ that could be occurred during the deformation of the other shear zones that affect the internal part of the Asir tectonic terrane. Two controversial tectonic meanings describe the tectonic evolution of the ASZ, the first one is the thin-skinned thrusting tectonic that indicating shallow earth s crust deformation and the second one is the occurrence of some ophiolitic slices that indicating suturing tectonic deformation. The absent of the complete ophiolitic section encourages us regarding the ASZ as a structural shearing zone rather than a suture zone.

A gravity and magnetic study of lithospheric architecture and structures of South China with implications for the distribution of plutons and mineral systems of the main metallogenic belts

• 3D density and susceptibility models of South China were inverted by gravity and magnetic data. • Lithospheric structure such as Moho of South China has been calculated and interpreted. • 5 source zones as well as pathways of mineral systems are clearly revealed. • Termination sites of mineral system are uncovered by 3D density and susceptibility models. South China is characterized by enormous volumes of igneous rocks generated by multiple stages of magmatism. Five large-scale metallogenic belts with many world-class deposits have been discovered, demonstrating great potential for prospecting new resources. To restrict the South China metallogenic cognition the main problems include the types and metal associations of the deposits, factors controlling the distribution of the different types of metallogenic belts, and targets for new deposits. To find possible and feasible solutions to solve these problems. It is necessary to consider the metallogenic factors from the concept of mineral systems. This study first converted the satellite gravity into Bouguer gravity under spherical coordinates. Then the reduction-to-the pole (RTP) magnetic anomalies were obtained using a moving window with different geomagnetic parameters. The vertical lithospheric interfaces and main faults were inverted and interpreted according to these gravity and magnetic data. Based on the results obtained, we have discussed the possible sources and pathways of the five metallogenic belts in South China. Meanwhile, it identified the 3D spatial distribution of intrusions qualitatively by inverted susceptibility and density model, and predicted the potential sites for Cu, Fe, Au, W, and Sn deposits.

Magnetic characteristics of a part of Closepet Granite, Eastern Dharwar Craton

The exposed granite gneissic complex to the west of Cuddapah basin in Eastern Dharwar Craton (EDC) is studied to understand the magnetic character of various plutons in this region with more emphasis on a part of Closepet Granite (CG). The NW–SE trending plutons in this region show gradual decrease in magnetic intensities from southwest to northeast; CG in the southwest corner of the study area have high mafic content, and there onwards show a depletion in mantle enrichment towards NE. Parts of the CG namely, the main mass and northern intrusions separated by a gap zone are differentiated based on magnetic character deduced by processing the aeromagnetic data. Reduced to the pole (RTP) and its upward continued maps revealed NNW trending eastward convex anomaly highs inferring the magnetic nature of CG due to Porphyritic Monzogranite (PMG). Gap zone is identified to be structurally significant, bounded by deep ENE faults and inferred to be associated with PMG at relatively deeper levels. 2.5D modelling of magnetic anomaly profile substantiated our qualitative analysis of magnetic anomalies over CG, inferring magnetic and non-magnetic units of CG. Known shear zones running north–south are identified with a few inferred shears revealed from magnetic data interpretation within CG.

Low-latitude reduction-to-the-pole and upward continuation between arbitrary surfaces based on the partial differential equation framework

SUMMARY Magnetic surveys conducted in complex conditions, such as low magnetic latitudes, uneven observation surfaces, or above high-susceptibility sources, pose significant challenges for obtaining stable solutions for reduction-to-the-pole (RTP) and upward-continuation processing on arbitrary surfaces. To tackle these challenges, in this study, we propose constructing an equivalent-susceptibility model based on the partial differential equation (PDE) framework in the space domain. A multilayer equivalent-susceptibility method was used for RTP and upward-continuation operations, thus allowing for application on undulating observation surfaces and strong self-demagnetization effect in a non-uniform mesh. A novel positivity constraint is introduced to improve the accuracy and efficiency of the inversion. We analysed the effect of the depth-weighting function in the inversion of equivalent susceptibility for RTP and upward-continuation reproduction. Iterative and direct solvers were utilized and compared in solving the large, sparse, non-symmetric and ill-conditioned system of linear equations produced by PDE-based equivalent-source construction. Two synthetic models were used to illustrate the efficiency and accuracy of the proposed method in processing both ground and airborne magnetic data. Aeromagnetic and ground data collected in Brazil at a low magnetic latitude region were used to validate the proposed method for processing RTP and upward-continuation operations on magnetic data sets with strong self-demagnetization.

Delineation of structure elements and the basement depth at the Jifara plain NW LIBYA using integration application of potential field dataset

In this study, the analysis of ground gravity data (from the Libyan Petroleum Institute) and aeromagnetic data (from the African Magnetic Mapping Project) are used to delineate the structure elements and basement depth within the Jifara plain, northwest Libya. A high-pass filter and a reduction-to-the-pole (RTP) transformation are applied to the gravity and aeromagnetic data respectively. The Total horizontal gradient and Centre for Exploration Targeting (CET) grid analysis are applied to gravity datasets. Werner deconvolution is applied to the RTP magnetic data. One 2-D forward modelling profile is applied to gravity and magnetic dataset. The results show gravity anomaly highs and magnetic anomaly with different structure trends. Werner deconvolution profile shows a high-density intrusion (about 1.8 km from the surface) within the sedimentary sequence. The intrusion may be the result of the Eocene volcanic activities near the Gharyan region. The 2-D model shows that the basement depth of Jifara plain ranges from 2.8 to 3.0 km. The integration results of the gravity and magnetic dataset reflect various periods of tectonic activities within Jifara plain and the adjacent area.