Gravity Anomaly Maps Research Articles

New free-Air and Bouguer Gravity Anomalies Maps of Brazil

Here we perform the integration of all available data from the BNDG (Banco Nacional de Dados Gravimétricos) and the BDEP (Banco de Dados de Exploração e Produção da Agência Brasileira de Petróleo) to provide new free-air and Bouguer gravity anomaly maps for the Brazilian territory with newly acquired data over the years, mainly in regions with no data coverage in the past. Quality controls and subsequent gridding processes, in the same system of the whole dataset, are developed on the Oasis Montaj software (OM). Subsets of data from various gravity surveys are gridded and upward continued up to 3000 m to avoid high-frequency noise, allowing them to be gathered. We fill areas with no data coverage in the North Region of Brazil with gravity values from the XGM2019e geopotential model. To join the subset grids of ground and airborne surveys and the geopotential model, we use a collection of grids knitting methods from the OM. To verify the consistency of our grids, we compare them with previously derived gravity anomalies maps and geopotential models. Our new free-air and Bouguer gravity anomalies maps showmore detailed short-wavelength geological structures than their predecessors. Therefore, these new gravity anomalies maps may be helpful for the development of recent tectonic, oil, and mining studies.

Crustal Mapping of Northern Extremity of Aravalli Delhi Fold Belt (ADFB) by High Resolution Gravity Survey in Haryana, India

Abstract Gravity data at a grid spacing of 2.5 sq. km., acquired by Geological Survey of India (GSI), have been analysed to discern the subsurface disposition of northern extremity of the Aravalli Delhi Fold Belt (ADFB). Geologically, the area has sparse exposure of the Aravalli Delhi Fold Belt and is predominantly covered by alluvium of Quaternary age. Apart from Bouguer gravity anomaly (BGA) map, residual gravity map, regional gravity map, radially averaged power spectrum (RAPS) and 3D Euler deconvolution maps have been prepared for better insights of the subsurface. Two 2D subsurface gravity models describe possible upwarpment of crustal and mantle materials for gravity high in southwest part of the study area. The significant change in trend of gravity contour pattern from NE-SW to NW-SE near Rohtak and further north is closely parallel to the trends of ADFB and Delhi Sargodha Subsurface ridge respectively. This deflection of the ADFB may probably be caused by rotation related to collision of plates. Earthquake data from International Seismological Centre (ISC), since the year 2000, has been used in the study. The earthquake data shows cluster of shallow focus earthquakes (from 2 to 39 km) with low magnitudes (from ML 1.8 to 5) in the study area near Rohtak. The presence of subsurface disturbance north of Rohtak is well supported by cluster of 3D Euler solutions and distribution of seismicity in that region. The multimodal distribution of the earthquake hypocentres is correlating well with the 2D gravity model along the Bhiwani to Panipat section.

Support vector machine-based integration of AVIRIS NG hyperspectral and ground geophysical data for identifying potential zones for chromite exploration – A study in Tamil Nadu, India

In the present study, we have integrated the spectral anomaly map derived from airborne visible-infrared imaging spectrometer-next generation (AVIRIS-NG) data and residual ground geophysical anomaly maps (gravity and magnetic) for identifying the mafic cumulates and chromitites in the Sittampundi Layered-Complex (SLC), Tamil Nadu, India. A spectral map of chromite bearing mafic cumulates was prepared by implementing the matched filtering (MF) algorithm on the selected spectral bands of AVIRIS-NG data using the mixed image spectra of mafic cumulate and chromitite as an end member. A low pass filter was applied in the spectral map to extract the clusters of coherently distributed spectrally anomalous pixels representing the surface exposure of mafic cumulates. Concurrently, the ground gravity and magnetic data were processed for deriving the residual gravity and magnetic anomaly maps. Subsequently, an integration of spectral map, residual gravity, and magnetic anomaly maps was attempted using the support vector machine (SVM) algorithm to identify the potential sites of chromitite occurrence. Results were verified using the geological map and the field data on surface exposures of mafic cumulates. This research demonstrates that integration of remote sensing data and geophysical anomaly maps has immense potential to detect the surface distribution of chromite bearing mafic cumulates in the layered complex and the same methods can be replicated for carrying out mineral prospecting in the other parts of the world.

A large-scale domal relief due to intraplate neotectonic compression in central Amazonia

In intracratonic South America, the origin of neotectonic activity and its impact on large Amazonian rivers have been of continuous research interest. Despite the low relief of the land surface, which has generally been attributed to tectonic stability, there is increasing evidence of Neogene fault reactivation within central Amazonia. Recent research has also reported surface folding during the Quaternary, but this record was based only on morphological analysis of remote sensing data. This investigation focuses on a megascale (~60,000 km2) domal relief from central Amazonia (the Juruá dome). It firstly aims to verify the domal relief relationship to folding. It then explores the origin of the stress field from which it has developed within the context of Andean uplift and the westward movement of the South American plate. The approach consisted of analyzing river adjustments based on morphological and morphometric information from remote sensing imagery, integrated with subsurface data Bouguer gravity and magnetic anomaly maps, well logs, and seismic reflection sections. The results revealed that the Juruá dome coincides with the location of a basin depocenter. Subsurface evidence exists for the growth of a broad anticline producing thicker sedimentary units away from the dome core. NE- and NW-striking normal and reverse faults with flower structure geometries are abundant and suggest deformation from strike-slip tectonics. Gravity and magnetic data revealed that the fold and many of its associated faults are deep-rooted into basement rocks. Within the analyzed stratigraphic interval, faults are mostly developed into pre-Cretaceous units, but often propagate to the surface, where they define the edges of the dome and partly deform its overall shape. The fold and its related faults have modified the course of several rivers within the domal relief area, including the Juruá River, which is entrenched along NE-striking faults that are configured to release stress along the fold axis. The geomorphological and structural data are collectively compatible with a long-term NW-trending maximum horizontal compressive stress-field that is driving basin inversion. This neotectonic activity can be linked to far-field stresses from the pushes from the Andean orogeny and the movement of the South American plate against the North Andean and Nazca plates.

Delineation of Subsurface Structures Using Gravity Data of the Shallow Offshore, Lamu Basin, Kenya

Lamu Basin is located in South Eastern Kenya and covers about 170 000 km2 both onshore and offshore. Kenya’s Lamu Basin is hitherto underexplored even though there have been notable oil and gas discoveries along the margin of East Africa. This study focuses on the shallow section of the Lamu offshore bounded by 39°E to 43°E by 2°S to 6°S, whereby, unfortunately, some of the wildcat wells turned out to be dry although expensive. Gravity interpretation techniques such as spectral analysis and first horizontal derivative were applied to the reduced gravity data to delineate and model structures to minimize the high investment risks. The gravity data used in this study were sourced from the International Gravity Bureau (BGI) and National Oil Corporation of Kenya (NOCK) digital data courtesy of companies like Woodside Energy, Anadarko Kenya Limited, and Total Exploration and Production companies. The obtained reduced gravity data were gridded to produce the gravity anomaly grids (Free air, Bouguer, and Isostacy), which were consequently drawn into maps. From spectral analysis, depths to shallow sources and deep sources were estimated. These depths were used to set regional and residual separation filters using the Gaussian filter. The first horizontal derivative (FHD) applied to the regional Isostatic gravity anomaly map yielded features that were inferred as intrasediment fractures/faults trending in NW-SE and NE-SW directions. The features like the ridges, troughs, and faults mainly trending in the NW-SE direction are discernable from the regional anomaly map. The developed models show the basement highs and lows with a possibility of anticlinal and synclinal structures and thick sedimentary successions likely to represent good hydrocarbon source kitchens.

An Integrated Lineament Extraction From Satellite Imagery and Gravity Anomaly Maps For Groundwater Exploration In The Gongola Basin

An Integrated Lineament Extraction From Satellite Imagery and Gravity Anomaly Maps For Groundwater Exploration In The Gongola Basin

Delineation of shallow structures in Madawara igneous complex, Bundelkhand Craton, India using gravity–magnetic data: Implication to tectonic evolution and mineralization

An integrated gravity–magnetic study has been carried out over Madawara Igneous Complex (MIC) in southern part of Bundelkhand Craton with an aim to decipher shallow crustal configuration and mineralized zones, thereby to improve the understanding of tectonic evolution of the region. Derived gravity and magnetic anomaly maps show good correlation with known geology and have delineated continuity of mafic–ultramafic intrusive bodies in EW direction. Radially averaged power spectrum (2D) and solutions derived from 3D Euler deconvolution have revealed average basement depths for gravity sources as ~0.3, 1.2 and 3.2 km, whereas for magnetic sources as ~0.3 and 1.2 km. From this study, these interfaces could be attributed to sedimentary origin for shallowest layer, mafic–ultramafic intrusive for intermediate layer and changes within the granite–gneissic basement for deeper solutions. Two-dimensional inverse modelling of residual gravity anomaly has delineated intrusion of highly dense mafic–ultramafic rocks from deeper part within the granite gneissic complex. Deeper basement from gravity and shallower from magnetic data indicate presence of two-stage magmatism within a subduction setting where the second magmatic emplacement probably occurred with a magma that comprises high magnetic material. High gravity and magnetic anomalies are observed over the mafic and ultramafic rock samples which are already identified (based on previous geochemical studies) as prospective zones for Cr, Ni and PGE mineralization. Thus, it can be inferred from this study that the mafic–ultramafic intrusive bodies are favourable targets for Cr–Ni–PGE mineralisation which may be obtained between a depth range of around 300 m to 3 km. Thus, the study enhances the scope for further integrated geophysical investigation over the identified prospective zones as well as provides important clues on magmatic evolution of the region.

Mapping of gold mineralization using 3D inversion magnetic data at Zone X, West Java

Gold mineralization occurs when the hydrothermal fluid rise beneath the earth’s surface. Tectonic activity causes gold mineralization in several depositional environments, one of which is a low epithermal sulfide deposite. This type of deposite is characterized by low temperatures and controlled by many geological structures. The discovery of veins in geological mapping in Zone X needs to be supported by geophysical exploration to identify the distribution of gold mineralized zones. This study aims to identify zones of gold mineralization based on magnetic data. From the results of the study obtained the susceptibility parameters of the 3D inversion process of magnetic data. The results are verified by map of gravity anomalies and geological structures. So that there are 2 interesting blocks which are interpreted as zones of gold mineralization in the southeast-northwest orientation and the depth of the dominant magnetic body at 900 masl to 20 masl.

Морфология Горихинского гранитного массива с помощью методов математической статистики

The Gorikhinsky granite massif is located in the marginal part of the Khentei highlands (Mongolian-Transbaikalian folded system, Central Mongolia). The massif is composed of coarse-grained weak-porphyry leucocratic granites, granite porphyry, and pegmatites. In the rocks of the massif, rock crystal deposits have been discovered. In certain pegmatite bodies, in addition to smoky quartz and morion crystals, the study has found the presence of fluorite, topaz, biotite, tourmaline, beryl, garnet, and allanite. The accessory minerals are cyrtolite, xenotime, zircon, sphene, rutile, apatite, cassiterite, etc. Thus, the study of the geological structure of the above object is of interest not only from a scientific but also from a practical point of view. The research data have become the basis for setting areal gravimetric work to determine the features of the massif’s geological structure. The work has been performed by the standard procedure using Scintrex Autograv CG-5 gravimeters. The height of the observation points has been determined by Trimble 5700 GPS devices. The RMS accuracy of the gravitational anomalies calculation as well as the density of the observation network meet the technical requirements for 1:100000 scale gravimetric surveys. Using the results of the gravity survey, a map of gravity anomalies in Bouguer has been compiled. Based on the interpretation of the map, with the use of the methods of mathematical statistics, quantitative characteristics of the shape and size of the body have been defined and a three-dimensional model of the massif has been built. For the purpose of the transformation and inversion of the gravitational field, the variance and regression methods of mathematical analysis have been used. The maximum thickness of the granites is 3.5 km; the area of the earth's surface projection is twice that of the granite outcrop. The obtained estimates are confirmed by the results of solving the inverse problem of gravimetry using the method of model selection. The article concludes that the use of the regression and variance analysis methods of mathematical statistics in the studies of the morphology of the intrusive bodies has proved most effective. The information on the shape and size of the massif will be used in concluding on the prospects of the massif’s metallogenic trend.

Appraisal of Potential Hydrocarbon Zones in Masila Oil Field, Yemen

Hydrocarbons serve the prime energy source of the world and the backbone to industrial development. Hydrocarbon potential is explored here using the spatial multi-criteria decision-making method. In order to demarcate the hydrocarbon potential zones within Masila oil field, Yemen, various thematic layers of multi-criteria factors affecting the hydrocarbons such as basement depth map (BDM), gravity anomaly map (GAM), magnetic anomaly map (MAM), subsurface faults system map (SFSM), upper syn-rift isopach map (USRIM), post-rift isopach map (PRIM), and lower syn-rift isopach map (LSRIM) were generated using the information extracted from both the geophysical and wells data available for the oil field. Geographical information system (GIS) techniques were used to generate various thematic maps that were subsequently converted to raster format and reclassified into various classes on the basis of their relative importance and the opinion of relevant experts. These thematic maps and their feature classes were assigned weights (eigenvalues) and rank by using the analytic hierarchy process (AHP) and following the theories of multi-criteria analysis (MCA). Furthermore, these maps were superimposed using the weighted linear combination (WLC) model on the GIS platform. The results of the integration of the thematic maps were classified into three classes representing the three hydrocarbon potential zones, namely, high potential zone (39.8%), moderate potential zone (49.1%), and low potential zone (11.1%). The cross plots of occurrence of the hydrocarbon reservoir, existing oil fields, and well locations were inferred for validation. The validation results revealed a good prospect for hydrocarbon potential in the study area. The novel quantitative approach used in the present study is capable of providing comprehensive results and assessment of hydrocarbons in the Masila oil field and other areas as well.

Conjugate utilization of Landsat-8 OLI, ground gravity and magnetic data for targeting mafic cumulates within anorthositic-layered complex of Sittampundi, India

In this article, we have processed Landsat-8 spectral bands, ground gravity, and magnetic data for delineating the mafic cumulates within the anorthositic-layered complex in Sittampundi, Tamilnadu, India. In this regard, surface anomaly map of mafic cumulates was derived by processing spectral bands of Operational Land Imager (OLI) sensor using matched filtering method. Residual gravity, magnetic anomaly maps are also derived. Spatial position of geophysical anomalies corroborate well with the spectral anomalies. A promising zone of chromitite occurrences is identified at the eastern fringe of the study area based on the concurrence of spectral and geophysical anomalies. Spatial profiles of geophysical and spectral anomalies around this promising zone are similar to the respective spatial profiles observed around the known chromite bearing mafic cumulates. Depth continuity of the mafic cumulates is confirmed by deriving of gravity and magnetic anomaly map at different depth using upward continuation filters to confirm concealed deposit.

Crustal structure of the Ulaanbaatar region, Mongolia according to gravimetric data

E stablish ing relationship s between the regional seismicity and the depth geometry and composition s of large -size density inhomogeneities of the upper crust is one of the ways to determine the p arameters of mean long-term seismicity . The origin of geological bodies and mechanism s of penetration of intrusive bodies in to the upper crust are detectable from the shape s and size s of such bodies. K nowledge o n the shape s and size s of large intrusive bodies is important for prospecting and exploration of mineral resources. Based on t he medium - scale areal gravimetric survey data, a regional map of Bouguer gravity anomalies was constructed for the Ulaanbaatar region , Central Mongolia. I nterpret ed gravimetric data from the sol utions of the inverse problem of gravimetry based on the body - shape selection were used to develop the 3D models showing the largest crustal density inhomogeneities of the study area – the Tolskaya ( Ula a n ba at a r) basin , Nalaiha depression and Bogdoulin granite massif. It is confirmed that the basement of these depression s has a block structure. The basement of the Tolskaya basin includes two depressions , the western and eastern ones . In the western depression, t he sediment thickness is 150 m . It amounts to 400 m i n the eastern depression at the intersection of the Selbin and Tolsk aya deep fault systems. The i nformation on the shape s and thicknesses of the sediment bodies is used in the seismic studies aimed at obtaining a more precise assessment of seismic hazard of the Ul a an ba at a r city and the region . In the Nalai ha depression, the sediments are 8 00 m thick . The morphology of the basement and the thickness of sediments in this depression can be used to update the mining prospects of the Nalaiha coal deposit. The maximum thickness of granitoids in the Bogdoulin massif is 9.0 km . T he area of its projection to the ground surface is twice as big as the area of the outcrops . Our research results can be useful for assessing the metallogenic specialization of granitoids, which indicators in relation to some minerals are related to the specific features o f the Bogdoulinsky massif . Such indicators have been discovered by the geological, geophysical and geochemical methods . Our study shows that t he geophysical methods (in particular, gravimetr y ) can considerably expand the knowledge of the morphology of geological objects at depth and facilitate reaching a new level in structural analysis, wh ich is critical for develop ing new ideas to clarify the geological history and tectonic conditions of the formation of the Mongolia-Siberian region.

Sonar and LiDAR investigation of lineaments offshore between central New England and the New England seamounts, USA

High-resolution multibeam echosounder (MBES) and light detection and ranging (LiDAR) data, combined with regional gravity and aeromagnetic anomaly maps of the western Gulf of Maine, reveal numerous lineaments between central New England and the New England seamounts. Most of these lineaments crosscut the NE-SWtrending accreted terranes, suggesting that they may be surface expressions of deep basement-rooted faults that have fractured upward through the overlying accreted terranes or may have formed by the upward push of magmas produced by the New England hotspot. The 1755 Cape Ann earthquake may have occurred on a fault associated with one of these lineaments. The MBES data also reveal a NW-SE-oriented scarp just offshore from Biddeford Pool, Maine (Biddeford Pool scarp), a 60-km-long, 20-km-wide Isles of Shoals lineament zone just offshore from southeastern New Hampshire, a 50-m-long zone of mostly low-lying, WNW-ESE-trending, submerged ridge-like features and scarps east of Boston, Massachusetts, and a ~180-km-long, WNW-ESE-trending Olympus lineament zone that traverses the continental margin south of Georges Bank. Three submarine canyons are sinistrally offset ~1–1.2 km along the Thresher canyon lineament of the Olympus lineament zone.

Titan's gravity field and interior structure after Cassini

Since its arrival at Saturn in 2004, Cassini performed nine flybys devoted to the determination of Titan's gravity field and its tidal variations. Here we present an updated gravity solution based on the final data set collected during the gravity-dedicated passes, before Cassini's plunge into Saturn's atmosphere. The data set includes an additional flyby (T110, March 2015, primarily devoted to imaging Titan's north polar lakes) carried out with the low-gain antenna. This flyby was particularly valuable because the closest approach occurred at a high latitude (75°N), over an area not previously sampled.Previously published gravity results (Iess et al., 2012) indicated that Titan is subject to large eccentricity tides in response to the time varying perturbing potential exerted by Saturn. The magnitude of the response quadrupole field, expressed in the tidal Love number k2, was used to infer the existence of an internal ocean. The new gravity field determination provides an improved estimate of k2 of about 0.62, accurate to a level of a few percent. The value is higher than the simplest models of Titan suggest and the interpretation is unclear; possibilities include a high density ocean (as high as 1300 kg/m3), a partially viscous response of the deeper region, or a dynamic contribution to the tidal response. The new solution includes higher degree and order harmonic coefficients (up to 5) and offers an improved map of gravity anomalies. The geoid is poorly correlated with the topography, implying strong compensation. In addition, the updated geoid and its associated uncertainty could be used to refine the gravity-altimetry correlation analysis and for improved interpretation of radar altimetric data.

Compiled potential field data and seismic surveys across the Eastern Brazilian continental margin integrated with new magnetometric profiles and stratigraphic configuration for Trindade Island, South Atlantic, Brazil

ABSTRACTThis work discusses the regional geological and geophysical datasets (potential field data coupled with seismic lines) available across the Eastern Brazilian Continental Margin and addresses tectonic models that have been applied to the geological interpretation of the Vitória-Trindade Chain (VTC). New magnetic data acquired in the Trindade Island is combined with compiled petrological data and geological maps to propose a stratigraphic column with radiometric control for the volcanic sequences. The gravity and magnetic anomaly maps were integrated with regional seismic profiles extending from the continental platform towards the oceanic crust, showing the geomorphology of the Abrolhos Volcanic Complex (AVC) and the VTC. A detailed geological mapping of the Trindade Island was complemented by magnetometric profiles acquired on the island. The magmatic episodes identified in the Trindade Island within different volcano-stratigraphic sequences are, geochronologically, dated by 40Ar/39Ar method as Late Neogene to Quaternary (Pliocene/Upper Pleistocene) and indicate intrusive and extrusive igneous rocks formed on the Mesozoic (Cretaceous) oceanic crust. Models for the emplacement of these volcanic rocks on much older oceanic crust include hotspots and leaking fracture zones. The presence of flat tops as observed in the volcanic banks and seamounts along the Vitória-Trindade volcanic chain indicate abrasion of much higher volcanic edifices that now form the isolated islands in the Trindade-Martin Vaz Archipelago. Geological mapping and detailed magnetometric surveys suggest different rock properties for distinct volcanic episodes that formed the Trindade Island. The remarkable pattern of magnetic anomalies trending NE-SW in the deep-water region of the Espírito Santo Basin, eastwards of the AVC, suggests that the linear chain of volcanic edifices in the VTC may be associated with mantle anomalies caused by a hotspot or plume that was influenced by the E-W direction of leaking transform fracture zones.Abbreviation: Abrolhos Volcanic Complex (AVC); Vitória-Trindade Chain (VTC)

Determination of maximum tilt angle from analytic signal amplitude of magnetic data by the curvature-based method

Imaging buried geological boundaries is one of a major objective during the interpretation of magnetic field data in Geophysics. Therefore, edge detection and edge enhancement techniques assist a crucial role on this aim. Most of the existing edge detector methods require to obtain special points such as in general the maxima of the resulting image. One of the useful tools in estimating edges from magnetic data is the tilt angle of the analytical signal amplitude due to its value slightly dependence on the direction of magnetization. In this study, the maxima of the tilt angle of analytical signal amplitudes of the magnetic data was determined by a curvature-based method. The technique is based on fitting a quadratic surface over a 3×3 windows of the grid for locating any appropriate critical point that is near the centre of the window. The algorithm is built in Matlab environment. The feasibility of the algorithm is demonstrated in two cases of synthetic data as well as on real magnetic data from Tu Chinh-Vung May area. The source code is available from the authors on request.ReferencesAkpınar Z., Gürsoy H., Tatar O., Büyüksaraç A., Koçbulut F., Piper, JDA., 2016. Geophysical analysis of fault geometry and volcanic activity in the Erzincan Basin, Central Turkey, Complex evolution of a mature pull-apart basin. Journal of Asian Earth Sciences, 116, 97-114. Beiki M., 2010. Analytic signals of gravity gradient tensor and their application to estimate source location, Geophysics, 75(6), 159-174.Blakely R. J., and Simpson R.W., 1986. Approximating edges of source bodies from magnetic or gravity anomalies, Geophysics, 51, 1494-1498.Chen An-Guo, Zhou Tao-Fa, Liu Dong-Jia, Zhang Shu, 2017. Application of an enhanced theta-based filter for potential field edge detection: a case study of the LUZONG ORE DISTRICT, Chinese Journal of Geophysics, 60(2), 203-218.Cooper G.RJ., 2014. Reducing the dependence of the analytic signal amplitude of aeromagnetic data on the source vector direction, Geophysics, 79, 55-60.Cordell L., 1979. Gravimetric Expression of Graben Faulting in Santa Fe Country and theEspanola Basin, New Mexico. In Ingersoll, R.V., Ed., Guidebook to Santa Fe Country, New Mexico Geological Society, Socorro, 59-64.Cordell L and Grauch V.J.S., 1985. Mapping Basement Magnetization Zones from Aeromagnetic Data in the San Juan Basin, New Mexico, The Utility of Regional Gravity and Magnetic Anomaly Maps, Society of Exploration Geophysicists, Tulsa, 181-197.Hsu S.K., Coppense D., Shyu C.T., 1996. High- resolution detection of geologic boundaries from potential field anomalies: An enhanced analytic signal technique, Geophysics, 61, 1947-1957.Le D.C., Application of seismic exploration methods to identify geological structural characteristics supporting for hydrocarbon potential assessment in TuChinh - Vung May basin, Ph.D. Thesis, Hanoi University of Mining and Geology.Li X., 2006. Understanding 3D analytic signal amplitude: Geophysics, 71(2), 13-16.Miller H.G. and Singh V., 1994. Potential Field Tilt a New Concept for Location of Potential Field Sources, Journal of Applied Geophysics, 32, 213-217.Nabighian M.N., 1972. The analytic signal of two-dimensional magnetic bodies with polygonal cross-section: Its properties and use of automated anomaly interpretation, Geophysics, 37, 507-517.Nguyen N.T., Bui V.N., Nguyen T.T.H., 2014. Determining the depth to the magnetic basement and fault systems in Tu Chinh - Vung May area by magnetic data interpretation, Journal of Marine Science and Technology, 14(4a), 16-25.Nguyen X.H, San T.N, Bae W., Hoang M.C, 2014. Formation mechanism and petroleum system of tertiary sedimentary basins, offshore Vietnam, Energy Sources, Part A, 36, 1634-1649.Phillips J.D., Hansen R.O. and Blakely R.J., 2007. The use of curvature in potential-field interpretation, Exploration Geophysics, 38(2), 111-119.Rao D.B., and Babu N.R., 1991. A rapid method for three-dimensional modeling of magnetic anomalies, Geophysics, 56(11), 1729-1737.Roest W.R., Verhoef J., and Pilkington M., 1992. Magnetic interpretation using the 3-D analytic signal, Geophysics, 57, 116-125.Tran N., 2017. Sediment geology of Vietnam, VNU Press.Tran T.D., Tran N., Nguyen T.H., Dinh X.T., Pham B.N., Nguyen T.T., Tran T.T.T.N., Nguyen T.H.T., 2018. The Miocenedepositional geological evolution of Phu Khanh, Nam Con Son and Tu Chinh - Vung May basins in Vietnam continental shelf, VNU Journal of Science: Earth and Environmental Sciences, 34(1), 112-135.Vo T.S., Le H.M., Luu V.H., 2005. Three-dimensional analytic signal method and its application in interpretation of aeromagnetic anomaly maps in the Tuan Giao region, Proceedings of the 4th geophysical scientific and technical conference of Vietnam, Publisher of Science and Engineering 2005.Wijns C, Perez C and Kowalczyk P, 2005, Theta map: Edge detection in magnetic data, Geophysics, 70, 39-43.

Using Gravity and Magnetic Data for Insights into the Mesoproterozoic St. Francois Terrane, Southeast Missouri: Implications for Iron Oxide Deposits

Gravity and magnetic data in conjunction with available drill hole data were used to decipher the nature of the volcanic lithologies and their relationship to iron oxide ore deposits within the northwest portion of the Mesoproterozoic St. Francois Terrane in southeast Missouri. Analyses of the data included creating a deep-seated gravity anomaly map by removing the gravitational effect of the Paleozoic sedimentary units, residual gravity and magnetic anomaly maps, and two and one-half dimensional gravity and magnetic models. The residual gravity and magnetic anomaly maps highlighted a series of short-wavelength maxima and minima anomalies that could be interpreted to be granitic within collapsed caldera systems surrounded later by ring intrusions. The gravity and magnetic models illustrate that the sources of the anomalies are situated mainly within the upper 5 km of the crust and help to constrain the location of suspected calderas. The iron oxide deposits, some of which contain significant quantities of REE minerals, are rarely associated with both residual gravity and magnetic maxima but may be on the edge of these maxima and/or occur over gravity minima. The REE-rich Pea Ridge deposit is located over a gravity minimum where modeling shows the main ore body extending down to 1.5 km with a low-density region extending to 5 km below the ore body. The cause of this low-density body is unknown but may be associated with the formation of the ore deposit. Potential iron oxide deposits may occur to the south and southwest of Pea Ridge based on our analysis while to the northeast of the Pea Ridge deposit an anomaly pattern similar to that over Pea Ridge was found.

Lithologic boundaries from gravity and magnetic anomalies over Proterozoic Dalma volcanics

Dalma volcanics (DVs) has intruded the older Singhbhum Group of Metapelites. Despite DVs being rich in mineralisation, its boundaries are not clearly demarcated. Gravity and magnetic surveys have been attempted for mapping the boundaries in DVs. These surveys were made in the northern fringe of the DVs over an area of \(\sim \)0.70 \(\hbox {km}^{2}\) along 13 parallel lines at 50 m spacing. The data was acquired at \(\sim \)25 \(\hbox {m}\) spacing. The surveys were taken for determination of lithological boundaries, depths and nature of causative source using Euler depth solutions and radially averaged power spectrum (RAPS). Residual anomaly maps of gravity and magnetic intensity show the same trend as that of Bouguer gravity anomaly and total magnetic intensity anomaly map indicating towards shallow sources. The magnetic map in general follows the same pattern as that of gravity anomaly maps. The map shows coincident high gravity and magnetic anomalies. These anomalies together with resistivity signatures confirm that the northern fringe of DVs hosts volcanogenic massive sulphide settings. The Euler depth solution delineated the lateral boundaries and nature of the source. It seems that the source is of spherical nature lying within a depth range of 25–40 m. The obtained lithological (vertical) units from RAPS are between Lower DVs, Upper DVs and Singhbhum Group Metapelites at depths of \(\sim \)15, \(~\sim \)25 and \(\sim \)40 \(\hbox {m}\), respectively. The metallogeny is associated with the Upper DVs and the corresponding delineated lithological (vertical) unit is indicative of the top of the ore body. Good agreement is observed with the geological succession from the drilling data and resistivity data. The findings suggest that the northern fringe of DVs could be a preferred target for drilling.

Using Chebyshev Moments to Solve Problems of Suppression of High-Frequency Noises in Fields of Gravitational Anomalies

The work is devoted to the problem of improving the quality of anomalous gravitational fields by reducing the level of their high-frequency noise. A brief review of existing approaches and methods for suppressing high-frequency noise in the fields of gravitational anomalies is given. A method for filtering fields of gravitational anomalies based on the transformation performed in the Chebyshev moment domain is proposed. The paper presents empirically established values of coefficients, which can be useful for an unknown level of noise. Using the simulated map of gravity anomalies, it was demonstrated that the proposed denoising filter is comparable in speed and superior in quality of the result to the bilateral filter, wavelet–filter, non–local means filters as well as the Wiener filter, which is well proven in the preliminary processing of gravitational fields.

O-230 日本列島の基盤構造を示す新しい重力異常図の作成原理とその特徴(招待,21. テクトニクス,口頭発表,一般発表)

O-230 日本列島の基盤構造を示す新しい重力異常図の作成原理とその特徴(招待,21. テクトニクス,口頭発表,一般発表)