Analysis Of Magnetic Anomalies Research Articles

Structural and tectonic features of the Transcarpathian trough according to gravity and magnetic data

Based on the analysis and interpretation of gravity and magnetic field anomalies, we studiedthe peculiarities of fault tectonics, structural-tectonic structure (including salt dome tectonics) of the Transcarpathian trough. We identified signs of the manifestation of deep faults and other large structural-tectonic elements in anomalies of gravity and magnetic fields. We then traced these structural-tectonic units by comparing the morphology, intensity, dimensions, and directions of the typical anomalous zones in the gravitational and magnetic fields with the tectonic structure of the region.
 We used digital maps of gravitational and magnetic fields; averaging transforms and relief-shadow images, we mapped local gravimagnetic anomalies. Analysis of the spatial structure of the original gravimagnetic fields and their transforms and structural-tectonic maps yielded a reflection of large tectonic elements of fault tectonics, anticlinal and salt dome structures in the gravimagnetic fields. Based on gravimagnetic data, the tectonic structure of the Transcarpathian trough was clarified, and the boundaries of tectonic zones and microplates were traced. The zone of the Transcarpathian deep fault is identified as a tectonic zone traced by a band of intense local positive anomalies of the gravity field along the Flysch Carpathians to the border of the Marmarosh massif. It is limited by high gradients from the southwest and northeast and is a reflection of the Pieniny and Marmarosh rock zones. The zone of the Transcarpathian deep fault is considered a suture zone of the Inner and Flysch Carpathians. In the structure of the anomalous gravity field of the Transcarpathian trough, a number of local anomalies associated with salt stocks, as well as individual anomalies, expected to be connected to salt-bearing deposits, werefound.
 We confirmed the effectiveness of gravimagnetic methods in the geological conditions of the Transcarpathian trough to detect anticlinal structures, basement protrusions, which create favorable conditions for oil and gas traps in sedimentary strata. Interpreting anomalous gravimagnetic fields in combination with geological and tectonic materials is an important condition for the integral process of studying the geological and tectonic structure of the Earth’s crust in the Transcarpathian region.

Geodynamic Aspects of Magnetic Data Analysis and Tectonic–Paleomagnetic Mapping in the Easternmost Mediterranean: A Review

The Easternmost Mediterranean is a transition region from the ocean to the continent where the spreading and collision zones of the lithospheric plates join. The methodology of paleomagnetic mapping of the transition zones is based on combining geological and geophysical techniques for continental and oceanic platforms: magnetic data interpretation, paleomagnetic reconstructions, results of magnetized rock radiometric dating, satellite data analysis, tectonic–structural reconstructions, biogeographical studies, and utilization of different geophysical survey results. The satellite-derived gravity map reflects practically all significant tectonic units in the region, which assists us in the supposed paleomagnetic mapping. The satellite-derived and aeromagnetic maps with the tectonic features and the map of Curie discontinuity of Israel indicate the complexity of this region. Advanced magnetic data analysis supported by paleomagnetic data attraction and other geological–geophysical methods allowed the revealing of the block of oceanic crust with the Kiama paleomagnetic zone relating to the Early Permian age. A narrow reversely magnetized Earth crust block was revealed in the Lower Galilee. Some examples of advanced magnetic anomaly analysis are presented for several areas where the magnetization vector inclination is other than the modern direction: the Sea of Galilee, Carmel, Rosh-Ha-Ayin, Malqishon, and Hebron. In Israeli land, for the combined paleomagnetic mapping, the well-studied using paleomagnetic and radiometric methods (as well as tectonic–structural) areas were selected: (1) Makhtesh Ramon, (2) the Sea of Galilee with the adjoining zones, (3) Carmel, (4) Hula, and (5) Hermon. It is shown that the regional analysis of paleomagnetic data distribution played an essential role in detecting the influence of the recently recognized counterclockwise rotating mantle structure on the near-surface layers.

Seafloor and Ocean Crust Structure of the Kerguelen Plateau from Marine Geophysical and Satellite Altimetry Datasets

The volcanic Kerguelen Islands are formed on one of the world’s largest submarine plateaus. Located in the remote segment of the southern Indian Ocean close to Antarctica, the Kerguelen Plateau is notable for a complex tectonic origin and geologic formation related to the Cretaceous history of the continents. This is reflected in the varying age of the oceanic crust adjacent to the plateau and the highly heterogeneous bathymetry of the Kerguelen Plateau, with seafloor structure differing for the southern and northern segments. Remote sensing data derived from marine gravity and satellite radar altimetry surveys serve as an important source of information for mapping complex seafloor features. This study incorporates geospatial information from NOAA, EMAG2, WDMAM, ETOPO1, and EGM96 datasets to refine the extent and distribution of the extracted seafloor features. The cartographic joint analysis of topography, magnetic anomalies, tectonic and gravity grids is based on the integrated mapping performed using the Generic Mapping Tools (GMT) programming suite. Mapping of the submerged features (Broken Ridge, Crozet Islands, seafloor fabric, orientation, and frequency of magnetic anomalies) enables analysis of their correspondence with free-air gravity and magnetic anomalies, geodynamic setting, and seabed structure in the southwest Indian Ocean. The results show that integrating the datasets using advanced cartographic scripting language improves identification and visualization of the seabed objects. The results include 11 new maps of the region covering the Kerguelen Plateau and southwest Indian Ocean. This study contributes to increasing the knowledge of the seafloor structure in the French Southern and Antarctic Lands.

К вопросу о геологической природе неоднородностей кристаллического фундамента Восточно-Европейской платформы

Based on the analysis of gravitational and magnetic anomalies of the eastern part of the East European Platform, it is concluded that inhomogeneities caused by serpentinization processes are present in the Earth’s crust. This conclusion is confirmed by conducting geological and geophysical studies on reference objects with serpentinite outcrops.

Advanced magnetic survey system and method for detailed magnetic field mapping near the sea bottom using an autonomous underwater vehicle

Marine magnetic field surveys conducted near the sea bottom are useful in producing images of the oceanic crust in order to ascertain its volcanic eruption history, active hydrothermal systems, and hydrothermal deposit evolution. An autonomous underwater vehicle (AUV) can carry out self-controlled survey operations while maintaining a stable vehicle attitude at low altitudes above the seafloor. As a result of these benefits, AUVs have attracted attention for various missions. The total magnetic field intensity is generally used for subsurface magnetization images. Recently, vector magnetic anomaly analysis has been considered to be extremely effective for high-accuracy estimation of subsurface magnetization structures. However, correcting for the anomalous magnetic field produced by the vehicle body is one of the difficulties that hinders vector magnetic anomaly analysis. Therefore, we developed a magnetometer system designed for the AUV URASHIMA with a renewed navigation data distribution system. Experimental observation was carried out around a submarine mud volcano with a small magnetic anomaly off Tanegashima Island. The results show that correction for the magnetic field of the vehicle because of the attitude, especially for changes in pitch, is essential for near-bottom magnetic surveys using AUVs. Based on these results, we proposed a suitable data acquisition method to remove the pitching effects of the vehicle for figure-eight turns. Next, practical observation was carried out in the hydrothermal area, and the proposed correction method for magnetic data reduced the pitch variation effect. These results indicate that the correction for the magnetic field of the vehicle based using attitude data, especially for pitching variations, is required in order to obtain high-quality magnetic anomaly data using AUVs. However, a short-period variation of approximately 10 nT caused by abrupt pitch changes remains.

Detection and Analysis of Magnetic Field Anomalies over Surface Defects of Complex-Profile Parts

Detection and Analysis of Magnetic Field Anomalies over Surface Defects of Complex-Profile Parts

Thermomagnetic properties of the upper crust in Central Anatolian Crystalline Complex-CACC (Turkey) from spectral analysis of magnetic anomalies

Thermomagnetic properties of the upper crust in Central Anatolian Crystalline Complex-CACC (Turkey) from spectral analysis of magnetic anomalies

Quantitative analysis of total magnetic anomaly maps on archaeological sites—Part 2

In this study, which is the second part of quantitative analysis of total magnetic anomaly maps on archaeological sites, it is aimed to analyze the depth values of potential buried structures that cause anomalies from the total magnetic anomaly maps of an archaeological excavation area. In the first step, depth values of the structures whose boundaries were determined on the improved total magnetic anomaly map of the model were analyzed. Depth values of blocks were calculated by using of tilt angle depth (TAD), source parameter imaging (SPI), and improved source parameter imaging (iSPI) methods. In the second step, the depth values at these boundaries were calculated. The total magnetic anomaly map of the mound area, for which the structure boundary analysis was made was calculated, and the depth values at the potential structure boundaries were calculated. Finally, the depth values are visualized on the simplified structure map of the region by combining and simplifying the potential structure boundary locations.

Quantitative analysis of total magnetic anomaly maps on archaeological sites—Part 1

In this study, which is the first part of quantitative analysis of total magnetic anomaly maps on archaeological sites, it is aimed to analyze the horizontal boundary values of potential buried structures that cause anomalies from the total magnetic anomaly maps of an archaeological excavation area. In the first step, the model was created in accordance with the archaeological structure. Noisy and noiseless anomaly maps of this model were calculated. These maps were enhanced using the reduction to pole and upward continuation methods. Tilt angle and automatic gain control methods were used. The responses of these methods on the total magnetic anomaly maps of the model were analyzed. In the second step, by applying the same procedures on the total magnetic anomaly map obtained from the magnetic measurements on the area that has not been excavated in the Amasya Oluz Mound archaeological excavation area, the horizontal boundaries of the potential structure elements of the region were analyzed.

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.

Application of Airborne Electromagnetics and Magnetics for Mineral Exploration in the Baishiquan–Hongliujing Area, Northwest China

Airborne electromagnetics is an effective and efficient exploration tool in shallow mineral exploration for its high efficiency and low cost. In 2016, airborne electromagnetic and airborne magnetic surveys have been carried out at the border of Xinjiang Uygur Autonomous Region and Gansu Province, the Northwest China. With an integrated system, the airborne electromagnetics and airborne magnetic data were collected simultaneously by AreoTEM-IV system from Aeroquest International Limited in Vancouver, BC, Canada, and the CS3 Cesium Vapor magnetometer from Scintrex in Concord, ON, Canada. About 3149 line-km of both data with 250 m line space were acquired. After data processing, the comprehensive analysis and interpretation of resistivity and magnetic anomalies has been carried out to infer lithological structure and outline the potential ore deposits. Verified by the ground surveys, seven outlined anomalies are consistent with the known ore sites, and one new gold deposit and several mineralization clues were found. The prospective reserves of gold are expected to exceed 10 tons. Besides, some prospecting target areas were outlined as the possible locations of copper–nickel deposits. The successful case shows the airborne magnetic data accords with geological structures, and the airborne electromagnetic method is effective in finding metal mineral resources, which can help to quickly identify potential ore targets with no surface outcrop.

A fault-bounded palaeo-lake basin preserved beneath the Greenland Ice Sheet

Subglacial topography not only exerts strong controls on contemporary ice sheet dynamics, but also provides an important long-term record of landscape evolution pertaining to past glacial and interglacial conditions. In particular, the bed topography beneath the Greenland Ice Sheet bears the signatures of past processes of landscape evolution that record the development of the ice sheet since its inception. Here we present evidence from airborne radio-echo sounding, gravity, and magnetic data for an enclosed palaeo-lake basin situated beneath the ice sheet in northwest Greenland. Geomorphological analysis and hydrological modelling indicate that the basin once hosted a lake with a surface area of up to ∼7,100 km2 and a volume of up to ∼580 km3. The basin and associated topography control the organisation of a preserved palaeo-fluvial channel network, suggesting that the basin pre-dates widespread glaciation in northwest Greenland. We use flexural modelling to show that the morphology of the basin and surrounding topography is consistent with elastic plate flexure driven by mechanical displacement along a normal fault bounding the basin margin. Analysis of gravity and magnetic anomalies indicates that the basin contains a sedimentary infill up to ∼1.2 km thick, which may contain valuable records of past ice sheet extent and environmental conditions in northwest Greenland. We therefore propose that this newly identified palaeo-lake basin may be a promising target for future acquisition of ground-based active source seismic data and potential recovery of subglacial material by sub-ice drilling programs.

Determining Infracambrian Hormuz Salt and Basement Structures Offshore Abu Dhabi by Joint Analysis of Gravity and Magnetic Anomalies

SummaryHydrocarbon fields that are located offshore Abu Dhabi, United Arab Emirates (UAE), are known to be associated with undulating thick sedimentary sequences. These undulations are mostly influenced by variations in the depth of Infracambrian Hormuz salts that generate negative gravity anomalies. Nonetheless, a few known oil fields are uncorrelated with the airborne gravity observations. This is attributed to the interference from large positive gravity anomalies from basement highs. To filter out the effect of basement, we calculate the pseudogravity effect of the airborne magnetic anomalies and subtract it from the gravity anomalies. The resultant gravity anomalies mainly represent the effect of the salt domes. The results uncover deep salt structures and introduce potential traps for hydrocarbons that have proved difficult to map accurately with current seismic techniques. A nonlinear 3D inversion modeling of corrected magnetic and decreased gravity data is also used to determine the depth to basement and the Infracambrian Hormuz salts over two regions. Our findings demonstrate that the depth to basement in these regions changes from 7100 to 9700 m, and the depth to Infracambrian Hormuz salt changes from 5800 to 9400 m, with a variable thickness with a maximum of 2700 m.

ГЕОФИЗИЧЕСКИЕ ИССЛЕДОВАНИЯ КЕРЧЕНСКО-ТАМАНСКОГО ШЕЛЬФА ЧЕРНОГО МОРЯ ПРИ ИНЖЕНЕРНОМ СТРОИТЕЛЬСТВЕ

The article presents the results of detailed geological and geophysical engineering work on the Kerch-Taman shelf. These works were carried out in order to identify potentially hazardous for engineering construction areas (for example, fault zones, local gas accumulations, etc.). The paper discusses methods for the selection of such sites, based on the analysis and joint interpretation of seismic materials and materials of marine magnetic surveys. A high degree of spatial coincidence of the areas identified by these independent methods was noted, which significantly increases the degree of reliability of their allocation. A number of geological section elements unfavorable for engineering construction have been detected and identified. The analysis of residual magnetic anomalies and their confinement to areas of discontinuous disturbances is considered in detail.

Basement faults deduction at a dumpsite using advanced analysis of gravity and magnetic anomalies

ABSTRACTA study of the fracture systems in the basement of the Matatlan urban waste dump of Guadalajara City, near the western edge of the Rio Grande de Santiago canyon (southwestern Mexico), is reported. The Matatlan dumpsite was developed on top of andesitic and rhyolitic rocks. Measurements at outcrops indicated that N–S (0°–15° and 165°–180°), N45–90E and N105–135E fracture systems affect the basement. Statistical analysis (micromagnetic method) of magnetic lineament azimuths indicated the presence of two lineament groups. The major one (N60–120E) has a maximum at N90–105E, and a secondary group (N120–165E). The gravity anomalies are featured by a major group (N60–120E, with maximums at N60–75E, and N105–120E) and a secondary group (N120–180E). Thus, a good to fair correlation exists between the measured fracture orientations and the lineaments featuring the gravity and magnetic anomalies. Horizontal derivative and tilt angle depicted horizontal limits of anomaly‐causative bodies. Results of the micromagnetic method are consistent with fracture orientations and with the limits established through edge‐detection techniques. Lineaments established by means of the gravity and magnetic Euler deconvolution are also consistent. Gravity and magnetic Euler deconvolution helped to estimate the depth extent of the limits of gravity and magnetic common sources. Euler deconvolution indicated the fault or contact nature of these lineaments. Furthermore, Euler deconvolution indicated slopes of the limits of gravity and magnetic sources. The fault or fracture nature of the major lineaments was finally confirmed by forward modelling (forward 2D cooperative modelling of gravity and magnetic profiles). For example, lineaments delimiting the northern depression could be characterized as normal faults. In general, this study indicates that it is possible, based on gravity and magnetic data, to characterize fractures affecting the basement of a dumpsite, a key parameter in hydrogeophysical studies. In particular, through this study, the inferred structures could be associated with regional tectonic faulting, which might provide migration paths to unhealthy lixiviate outside the dumpsite, giving rise to the contamination of the neighbouring environment. In particular, the study explains the presence of an unhealthy leachate waterfall to the northeast of the dumping site. Heavy metal contents in samples from this waterfall support that lixiviates originate at the dumpsite.

Analysis of magnetic field anomalies before earthquakes based on ULF (Ultra Low Frequency) method using magnetic sensor data in Sumatra

Sumatra has a complex tectonic system which it causes to be prone to earthquakes. Therefore, early warning before earthquake is needed with the study of earthquake precursors using Ultra Low Frequency (ULF) method. This method applied to the recording data of the Earth’s magnetic field for 30 to 3 days before the earthquake event. This study also carried out the prediction of earthquake magnitude and epicentre based on the amplitude of the anomaly and the distance of the station to the earthquake location. To ensure that the anomalies that occur are not due to external interference, the data is observed based on the Dst Index. In this study was found that the percentage of success was 74% approaching the actual data

Studies on the relationships of the Curie surface with heat flow and crustal structures in Yunnan Province, China, and its adjacent areas

A Curie surface indicates the distribution of the thermal fields underground, providing a clear marker for the thermodynamic effect in the crust and mantle. In this paper, based on a geomagnetic field model (NGDC-720) and aeromagnetic data, we use power spectrum analysis of magnetic anomalies to estimate the Curie surface in Yunnan Province, China, and its adjacent areas. By combining the distribution of the Curie surface with regional heat flow, the geothermal gradient, crustal wave velocity ratio anomalies, high-conductivity layer anomalies, and the Moho surface, we reveal the connection between the undulation of the magnetic basement and the crustal structures. The results indicate that the uplift and depression of the Curie surface in the research area are distinct. The Curie surface is approximately inversely correlated to the surface heat flow. The Lijiang-Jianchuan-Baoshan-Tengchong and Jianchuan- Chuxiong- Kunming-Yuxi zones are two Curie surface uplift zones, and their crust-mantle heat flows are relatively high. The Curie surface uplift zone along the Lijiang-Xiaojinhe fault and Red River fault is consistent with the heading direction of the fault zone and is partially in agreement with the eastward mass flow of the Tibetan Plateau. The Curie surface uplift zone is consistent with the high wave velocity ratio and high-conductivity layer anomaly region of the crust. The depth of the Curie surface is less than the depth of the Moho surface.

Oceanic plateau formation by seafloor spreading implied by Tamu Massif magnetic anomalies

Tamu Massif is an immense Mesozoic submarine volcano, the main edifice of the Shatsky Rise oceanic plateau. It is located at a spreading ridge triple junction, but considered to be a shield volcano formed by effusive volcanism from an emerging mantle plume. However, it is unclear how Tamu Massif eruptions interacted with the spreading ridges, which are enormous linear volcanoes themselves. Here we create a magnetic anomaly map for Tamu Massif, which can provide clues about crustal formation. For Tamu Massif, we find dominantly linear magnetic field anomalies caused by crustal blocks of opposite magnetic polarity. This pattern suggests that Tamu Massif is not a shield volcano, but was emplaced by voluminous, focused ridge volcanism. If the magma source at the Shatsky Rise was a plume, it was closely connected to and controlled by seafloor spreading. By implication, even the largest oceanic plateau edifices can be formed by seafloor spreading. We suggest that the widely accepted analogy between continental flood basalts and oceanic plateaus requires reconsideration. The Shatsky Rise oceanic plateau formed by spreading ridge volcanism, according to analyses of linear magnetic anomalies over the Tamu Massif submarine volcano.

Radiometric Surveys for Detection of Uranium in Dhofar Region, Sultanate of Oman

The Proterozoic basement of the Dhofar region of the Sultanate of Oman might be considered as a potential source of Uranium mineralization like other Proterozoic basins of the world, which collectively contribute 30%-40% to the global production. Uranium exploration assumes great importance in this part of the world and therefore geochemical and geophysical exploration for Uranium was initiated. Initial, random sampling of the study area with Gamma ray spectrometry as well as in situ XRF (Xray Florescence) analysis indicated the presence of around 30-40 ppm of Uranium. Since Gamma ray spectrometry results in the calculation of the heat produced during radioactive decay of Potassium (K), Uranium (U) and Thorium (Th) within the rocks in the study area, measurements were acquired along eleven traverses of varying length from 100-250 m at a traverse interval of 20 m and sampling interval of 10 m. Individual plots of the concentrations of radioelements such as U, K and Th have shown favorable anomalous radioactive sources. Besides this, Uranium to Thorium (eU/eTh) and Uranium to Potassium (eU/K) ratio plots have been presented and the alteration zones associated with Uranium mineralization through all traverses have been identified. Further, the generated composite ternary image based on the combination of K, Th and U from Gamma ray spectrometry determines different relative amounts of radioelements and paves the way for deciphering the level of radioactivity in the study area. However, there seems to be no presence of strong Uranium anomalies in the near surface of the limited study area. As the study area is heavily faulted, the depth to concealed subsurface fault structures is estimated to be around 64 m based on Hartley spectral analysis of total magnetic anomaly (line-6).

Contrastive analysis of gravity and magnetic anomalies between North China Craton and Indian Shield

The evolution correlation between the North China Craton (NCC) and the Indian Shield (IND) is very important for plate reconstruction. Recently, more and more research results show that the NCC and IND had been pieced together in the Paleoproterozoic. In order to analyse the correlation between the NCC and IND, we use the latest gravity and magnetic data to study deep geophysical characteristics of the NCC and IND respectively, and we also use a two‐dimensional discrete wavelet transform method to discuss the division scheme of the basement tectonic unit in the Paleoproterozoic at the point of gravity and magnetic field. On the basis of gravity and magnetic anomalies, the NCC is divided into the Eastern Block, Western Block, and the Trans‐North China Orogen, which are further divided into the secondary tectonic zones and blocks. The IND is divided into the Southern Block, the Northern Block, and the Central Indian Tectonic Zone, and they also are further divided into secondary tectonic zones and ancient cratons. On the basis of that, according to the four Paleoproterozoic plate assemblage schemes proposed by predecessors, we compared the geophysical characteristics and the correlation through the regional gravity and magnetic anomalies between the two continents. The results show that the faults and tectonic boundaries in the Trans‐North China Orogen of the NCC correspond well to those in the Central Indian Tectonic Zone of IND. Moreover, the gravitational and magnetic anomalies in the Eastern Block of the NCC are quite similar to those in the Southern Block of IND, which shows that the NCC and IND might have been pieced together during the Paleoproterozoic. The geophysical result that verifies the correlation between the NCC and IND based on gravity and magnetic fields provides the evidence for Paleoproterozoic plate reconstruction and constrains the assembling patterns between the NCC and the IND.