Gravity Map Research Articles

Appraisal of gravity-based lineaments around Central Indian Ridge (CIR) in different geological periods: Evidence of frequent ridge jumps in the southern block of CIR

• Application of edge Enhancement to mark the lineaments over the CNIR. • Power spectrum analysis to differentiate long and short lineaments. • Comparison of spreading rate with length of lineaments. • Analysis of lineament orientation and plate movement in different geologic era. • Southern CNIR witnessed frequent ridge jumps for stability of the RTJ . This paper presents an approach for utilizing the balanced edge detection technique in satellite-derived gravity data to study the tectonic movement in past geological periods. The research is initiated by examining the normalized total horizontal derivative (NTHD) edge detection technique based on a moving window. NTHD is found to be effective for both shallow and deep-seated bodies. The noise in the gravity map could be effectively eliminated using a larger window size. The lineaments are marked over the Central Indian Ridge (CIR) using NTHD. Analysis of various geological periods and the lineaments shows that the speed and direction of the tectonic Plate play an essential role in deciding the length and orientation of lineaments formed. The most prominent lineament pattern observed over the CIR is in the NE-SW, ENE-WSW, and NNE-SSW, possibly associated with plate movement during Late Cretaceous to Late Eocene and after the Early Miocene period. In addition, a few lineaments are also found to be oriented in NW-SE, E-W, and N-S. The N-S lineaments might be the consequence of the movement of the Indian Plate in a northward direction for a short time during the Late Eocene and Early Miocene. The E-W lineaments result from the transfer of the Reunion hotspot from the Indian to the African Plate. The high lineament density and circular statistical values indicate left flank of the CIR undergoes rigorous tectonic activity. The high value of circular statistics indicates the chaotic arrangement of lineaments in the southern block of the CIR.

Detecting sub-basalt Mesozoic sediments and active tectonics in the Narmada-Tapti Rift Zone, central India

To obtain structural information below basalt cover using conventional seismic reflection has always been a challenge due to the high impedance of the basaltic layer. This study enumerates P-wave refraction tomography to image the shallow structure along three long offset profiles in the Deccan Volcanic Province, one of the world's largest flood basalt volcanic regions. The travel time inversion is performed to obtain a starting model for the wavefield inversion, and synthetic tests are used to estimate the resolution. Our results show an abrupt increase of crystalline basement depth from 1.5 to 3 km across the Narmada South Fault. The shallow basement depth coincides with a 70-km-wide sub-basalt (>1.5 km deep) seismic shadow zone between the Narmada and Tapti rivers, associated with the sub-basalt graben caused by a crustal extension that contains sediments or a combination of basalt and sediments. The basaltic layer appears to be highly heterogeneous in velocity and thickness, and the degree of heterogeneity increases laterally and vertically with depth within the layer. It is quite likely that these sub-basalt sediments could be the potential zone for hydrocarbon, similar to the exposed Vindhyan in the north and Gondwana sediments in the south of our study area. Another intriguing feature is the Barwani Sukta Fault, which controls the tectonics of the region by dividing the basement configuration. We also compare our tomographic model with those determined from previously obtained seismic, gravity, and surface mapping. The tomographic image clearly shows that numerous faults are reaching up to the basement and extending laterally. We suggest that these neo-tectonic faults may be capable of generating large-magnitude earthquakes, including the 21 May 1997 (mb 6.0) Jabalpur earthquake.

The Quantification Method of Matching Capability of Areas in Gravity-Aided Inertial Navigation

Gravity-aided inertial navigation system (GAINS) is one of the essential research fields in underwater navigation technology, and one of the key problems to be solved is the selection of suitable matching areas. Distinctive from previous studies, the concept of Matching Capability of Areas (MCA) is defined from the perspective of the whole system, not just the 2-D image characteristics. The key factors affecting the MCA are analyzed, including heading, matching length, inertial navigation system (INS) initial position error, gravimeter error, map error, and INS drift. Taking these experimental conditions as a prior information, the method based on conditional probability to calculate the MCA is proposed, which can estimate the probability of matching within the required error limits in the given digital gravity map (DGM). After implementing a long-distance marine experiment, the validity of the MCA is verified and it is more comprehensive and effective than traditional characteristic parameters.

Imaging the Volcanic Structures Beneath Gran Canaria Island Using New Gravity Data

AbstractFrom a new gravity data set that covers homogeneously the whole surface of Gran Canaria (Canary Islands, Spain) and marine gravity data in the nearest offshore, we have obtained a Bouguer anomaly gravity map of the island which improves the previous ones. Using these gravity anomalies, we have applied a gravity inversion approach to investigate the structures beneath the surface of Gran Canaria Island and derive a 3D gravity sources model. The geometry of structures with anomalous density values is constrained up to a depth of approximately 20,000 m below the sea level. The interpretation of the density model identified structures related to the different volcanic stages of Gran Canaria. Several deep‐rooted high‐density structures represent the intrusive bodies emplaced in the early formation of Gran Canaria and the magma plumbing system of the Miocene volcanic edifices. A low‐density body in the center of the island may be associated with the syenitic core of the felsic central volcanic edifice (Tejeda Caldera). Shallow low‐density structures identified fractures which acted as feeder dikes of monogenetic volcanoes during the rejuvenated stage. Finally, the NW‐SE rift, which is the most important volcano‐tectonic structure of Gran Canaria, has a characteristic gravimetric signature and represents a long‐lived extensional fracture zone that has controlled the volcanic activity at least since the Miocene.

Structural setting of the Ischia resurgent caldera (southern Tyrrhenian Sea, Italy) by integrated 3D gravity inversion and geological models

Abstract The structural setting of the Ischia resurgent caldera and its magmatic system has been investigated by a joint interpretation of a 3D inversion of previously collected gravimetric data and all the available geological, geophysical and petrological data. Starting from the available Bouguer gravity map of the Neapolitan volcanic area and a previous 2.5D modelling, a selection of on land and offshore gravity data has been used to perform a 3D inversion, adapting and merging the basic ideas of two already tested methods, used to detect isolated bodies and layered discontinuities respectively. The base of the map is a set of gravity values, covering the whole Neapolitan volcanic area and the Gulf of Naples, which results from the union of 862 offshore and about 2000 on land extant gravity data, made uniform and re-analysed. The final model proposed here allows us to outline a very detailed and well-constrained structural setting of the crustal sector beneath Ischia. In particular, the 3D gravity inversion allowed us to outline a body with negative density contrast under Mt Epomeo, interpreted as the resurgent block, and to describe the magmatic system underneath it as a complex system of intrusions, rather than a uniformly distributed laccolithic body.

Evidence for paleo-continental margin and folding of relic fragment of oceanic lithosphere, northeast Indian subcontinent

The processes of continental breakup, reassembling of landmasses, and huge deltaic sediment depositions contribute to reconfiguring the Earth's surface. Here, we show a classic example of contiguous structures of paleo-continental margin on the eastern Indian Shield and an ancient fragment of the oceanic lithosphere beneath Bangladesh. In the present work, we collated gravity data from Bangladesh and adjoined parts of the Indian shield and the northern Bay of Bengal to decipher rocks' nature and long-term behavior. The gravity map illustrates N-S oriented alternate bands of ∼150 km wide positive and negative anomalies in the Bangladesh region, besides showing signatures of prominent geomorphic features such as the Shillong Plateau, Sylhet Trough, Burmese Arc, etc. The crustal models reveal the presence of paleo-continental margin segments on the eastern edge of the Singhbhum craton and south of the Shillong Plateau, ∼150 km wide folded oceanic crust beneath Bangladesh, and a low slab dip of the subducting Indian plate beneath the Burma platelet. The inferred continental margin evolved after the breakup occurred between the Rajmahal-Sylhet Line and continental fragments (Elan Bank and southern parts of the Kerguelen Plateau) at about 120 Ma. Subsequently, the sediments carried by two great Himalayan river systems were excessively deposited on the margin and over an older fragment of the oceanic lithosphere, resulting in the progradation of the Bengal delta towards the ocean. The oceanic crust beneath Bangladesh was folded with approximately 150 km wavelength as the compressive stress regime is locally operative due to the eastward moment of the Indian plate and westward propagation of the Indo-Burman Wedge.

Gravimetric contributions to the study of the collapsed structures in northeast Tadla Plain:structural and hydrogeological implications

This study was realized in the north-east of the plain of Tadla, in the region of Beni Mellal-khenifra, Morocco. The main aim of this research is to establish the geometry and hydrogeology characteristics of the region's aquifer system, based on the results of analysis and interpretation of deep-drilling data, and on gravimetric and electrical survey measurements. First, the regional gradient was determined, then the initial data was extracted, and based on the extracted data, we created the gravity map of the Bouguer, where the anomalies are clearer. The examination of the Bouguer anomaly's gravity map reveals the existence of a regional gradient. These anomalies are typically found in outcrop areas of the basement and differences in thickness of the sediment cover in the study area. The Electrical survey measurements, and the interpretation of the deep-drilling data, confirm the results of gravimetry survey, after applying different techniques such as horizontal gradiometer and upward extension, on the Gravimetric map. The founded results allowed us to draw up a structural map showing the system faults, which is accountable for the study area structure. The structural map is a very useful tool to guide future hydrogeological researches in the plain of Tadla.

Integrated geophysical and geochemical study for investigating the hydrocarbon potentiality of West Dakhla area, Western Desert, Egypt, as an extension of Libyan Kufra basin

The present study represents an integrated study using the potential field maps and well geochemical data of the West Dakhla area in the western central area of the Western Desert area, Egypt. The potential field data are represented by the airborne gravity and total magnetic maps acquired by the Nuclear Material Authority (NMA), Egypt, on behalf of Dana Petroleum Company. The geochemical data consist of geochemical analysis in Ammonite-1 well that were done for source rock evaluation. Different processing techniques on the gravity and magnetic maps are carried out for separating the regional and residual separation and filtering. Modelling and Euler deconvolution tools are utilized for proposing the depth to basement and constructing basement-depth maps to infer the basin configuration of the study area. Before acquiring the present geophysical data, the study area wasn't subjected to any exploration investigations. Therefore, these data and this study are considered as the first efforts carried out and submitted for publication in this area. In addition, a comparison of the present basin is done with matched basins in southern Libya, where this basin is expected to have similar geological features. The study indicates that the studied basin may be a part of a wider basin extending in Egypt and Libya. This basin is expected to have the thickness and features that are favourable for hydrocarbon habitat. The geochemical analysis shows TOC values ranging from poor to very good source rock potentiality.

Comparing GRACE-FO KBR and LRI Ranging Data with Focus on Carrier Frequency Variations

The GRACE Follow-On satellite mission measures distance variations between its two satellites in order to derive monthly gravity field maps, indicating mass variability on Earth on a scale of a few 100 km originating from hydrology, seismology, climatology and other sources. This mission hosts two ranging instruments, a conventional microwave system based on K(a)-band ranging (KBR) and a novel laser ranging instrument (LRI), both relying on interferometric phase readout. In this paper, we show how the phase measurements can be converted into range data using a time-dependent carrier frequency (or wavelength) that takes into account potential intraday variability in the microwave or laser frequency. Moreover, we analyze the KBR-LRI residuals and discuss which error and noise contributors limit the residuals at high and low Fourier frequencies. It turns out that the agreement between KBR and LRI biased range observations can be slightly improved by considering intraday carrier frequency variations in the processing. Although the effect is probably small enough to have little relevance for gravity field determination at the current precision level, this analysis is of relevance for detailed instrument characterization and potentially for future more precise missions.

Pitted-Ground Volcanoes on Mercury

On the planet Mercury, pyroclastic deposits formed by explosive volcanism are developed around rimless volcanic pits that are up to dozens of kilometers in diameters. Some pyroclastic deposits on Mercury, however, host no discernable main eruption centers but feature pitted-ground terrains that each consists of many similar sized and irregularly shaped pits. Individual pits are usually much smaller and shallower than typical volcanoes on Mercury. The origin of these landforms is unknown, but it is indicative of styles of volcanism on Mercury and/or post-volcanic modifications. Here, we investigate the possible origin of these peculiar landforms based on their geological context, morphology, geometry, reflectance spectra, and geophysical background. Reflectance spectra of pyroclastic deposits around such volcanoes are comparable with those erupted from typical volcanic pits on Mercury, suggesting a genetic relation between these pitted-ground terrains with explosive volcanism, and the source magma might have similar compositions. Pitted-ground volcanoes are mainly observed in impact structures, and two cases were formed in high-reflectance smooth plains and channeled lava flows. Most pitted-ground volcanoes are relatively degraded compared with typical volcanoes on Mercury, and some might have been formed in geological recent times judged by both their pristine preservation and crosscutting relationship with impact rays. All pitted-ground volcanoes have unconfined morphology boundaries, and each case is composed by dozens of rimless pits that have similar preservation states and interconnected edges. Such morphological characteristics are unique among volcanic landforms on terrestrial bodies, and they cannot be explained by multiple post-eruption collapses of a main explosive volcano. Pitted-ground volcanoes that are developed in lava flows with the same age have different preservation states, suggesting that the pits were not formed by escape of thermally destabilized volatiles from substrate and subsequent roof collapses. The largest pitted-ground volcano (~3700 km2) is located on the Borealis Planitia, and Bouguer gravity data reveal no larger mass concentration in the subsurface than surrounding terrains, consistent with a paucity of shallow intrusions in the crust of Mercury. Short-term and spatially-clustered explosive eruptions could explain the peculiar morphology and geometry of the pits, suggesting that pits in a given pitted-ground volcano are akin to swarms of monogenetic volcanoes. However, possible magma dynamics for the formation of pitted-ground volcanoes cannot be confirmed until future high-resolution gravity mapping could reveal detailed interior structures beneath these volcanoes. Based on comparative studies with spatially-clustered and similarly aged volcanoes on Earth, we interpret that a combination of pervasive crustal fractures and regional thermal anomaly in the thin mantle of Mercury might have caused such short-term and spatially-clustered explosive eruptions. If this interpretation was true, the heavy degradation state of most pitted-ground volcanoes and the few well-preserved cases are consistent with an overall cooling trend of the mantle, indicating the existence of longstanding heterogeneous thermal structures in the mantle.

Bouguer and mantle gravity maps of Nigeria

We used global gravitational models together with topographic, bathymetric, and lithospheric density structure datasets to compile Bouguer and mantle gravity maps of Nigeria, and then used these gravity maps to interpret the crustal and upper mantle structure in this country. We applied methods for a spherical harmonic analysis and synthesis of gravitational and lithospheric density structure models to produce both gravity maps. Whereas existing Bouguer gravity datasets for different parts of Nigeria were computed by applying only a simple planar Bouguer gravity reduction and a planar terrain gravity correction, our approach took into consideration the Earth’s spherical approximation and the spherical terrain correction, the ocean density contrast as well as density variations within sediments and the underlying consolidated crust. This study also provides the first mantle gravity map of Nigeria. Our results show that the free-air gravity pattern reflects mainly a topographic relief with prevailing positive values over topographically elevated regions, while Cretaceous sedimentary basins are characterized by low negative values. The pattern in the Bouguer gravity map exhibits mainly a Moho signature, with low negative values associated with a regional Moho deepening beneath the Sokoto Basin and the North Shield Belt. The pattern in the mantle gravity map exhibits a thermal signature of the lithospheric mantle. The high values (≥ 1000 mGal) of the mantle gravity disturbances detected over the Benin-Nigerian Block and the Phanerozoic cover of the West African Mobile Zone are possibly associated with a thermal signature of the lithospheric mantle. Another thermal signature of the lithospheric mantle along the Cameroon Volcanic Line partially outlines margins between the Oubanguides Neoproterozoic Belt and the southern extension of the West African Mobile Zone.

Application of Microgravity Survey in the Exploration of Rare-metal Bearing Pegmatites – A Case Study from Marlagalla, Mandya District, Karnataka

Abstract Geologically, the Marlagalla area represents the southern part of NNE-SSW trending Nagamangala schist belt, which is a member of ancient supracrustals of Sargur Group and situated in the southern part of Western Dharwar Craton. The area is mostly soil cover with limited exposure of amphibolite/hornblende schist and intrusive pegmatite. Pegmatites occur as lensoidal bodies within the amphibolite.Microgravity surveys are attempted for the first time to detect pegmatites within the amphibolite. The density between pegmatite (Density= 2.58-2.61 gm/cc) and host rock amphibolite (Density=3.09-3.14 gm/cc) gives detectable contrast to identify pegmatite within amphibolite. Gravity data are acquired over a grid of 5m x 30m using CG-5 Autograv gravimeter which has 1 μGal sensitivity. Elevation data are acquired using SP80 post processing DGPS instrument which has 5 mm elevation accuracy. Analysis of residual gravity and first vertical derivative (FVD) filters facilitated in delineating the pegmatite bodies. The pegmatite bodies show low gravity anomalies with an amplitude range of -5 to -200 μGal. FVD map of the residual gravity indicated four major N100E trending linear anomalies of -36 to 3.0 μGal/m corresponding to pegmatite bodies of varying strike (100-200m) and width (10-15m).2D-Forward modeling of microgravity data helped in deriving the subsurface geometry of the pegmatites. Borehole drilled subsequently based on the results of microgravity surveys intercepted pegmatites within the amphibolite. Thus, the technique has proved for exploration of pegmatite in contrasting environment of amphibolite. Pegmatite are known for rare metals and lithium minerals. Indirectly the model proposed here will help in exploration of rare metals and Li bearing pegmatite.

North America's Midcontinent Rift magma volume: A coincidental rendezvous of a plume with a rift

Abstract The Midcontinent Rift of North America is a ca. 1.1 Ga, 3000-km-long failed rift that nearly split the Precambrian continent of Laurentia. Unlike most continental rifts, which are filled with a mixture of volcanic rocks and sediments, the Midcontinent Rift contains a large volume of flood basalts that were emplaced during both syn- and post-rift stages. Consequently, the Midcontinent Rift, which comprises the Keweenaw large igneous province, is the most significant positive anomaly on gravity maps of central North America. We investigated the mantle conditions required to produce this large volume of flood basalt and the observed two main stages of emplacement. To explore whether these magma volumes required a plume or, instead, could have resulted from the increased ambient mantle temperatures expected for the Neoproterozoic, we used a geodynamic model for a range of ambient mantle and plume temperatures under different scenarios of lithospheric extension. The most favorable scenario for the generation of both syn-rift and post-rift lavas combines a plume with excess temperatures between 175 and 225 °C introduced during the syn-rift phase and ambient mantle potential temperatures between 1393 and 1443 °C, with an initial lithospheric thickness not exceeding 150 km for 3 mm/yr extension rates.

Determining the Tectonic Implication Derived from Geophysical Data of Bahr An-Najaf Basin, SW Iraq

Free-air gravity, magnetic and topographic data derived from satellite imagery are used to study the main geological structures and features in the Bahr An-Najaf Area SW Iraq. A comparison between this map and gravitational and magnetic maps along with two profiles, each one on a map for the same location and direction. Both profiles show a decrease in values in the eastward direction of the two maps. The total magnetic intensity data of the study area are converted to reduction to pole data and drawn as a magnetic map. It is clear from the reduction to pole map that the rates of uplift and subsidence that occurred in the basement rocks are due to the faults in the Bahr An-Najaf region. The location of the Bahr An-Najaf Depression coincided with the negative anomalies on both the free-air gravity map and the reduction to pole magnetic map. Both maps are also used to define the important faults in the area, especially the Abu Jir Fault.

SELECTION OF AN OPTIMUM GLOBAL GRAVITATIONAL MODEL FOR GEOLOGICAL MAPPING OF AFIKPO AND ANAMBRA BASINS IN NIGERIA

Combined Global Gravitational Models (GGMs) are being used in numerous geoscience applications, most notably for gravimetric geoid modeling (in geodesy) and for geological mapping and geophysical explorations (in the Earth’s sciences). The aim of this study is to evaluate the suitability of different combined GGMs that could be used for the geological mapping of middle belt region and Southeastern Nigeria. For this purpose, we digitized geological maps of Afikpo and Anambra Basins to evaluate geological signatures implied by gravity field quantities (Bouguer gravity anomalies and vertical gravity gradient) derived from the EGM2008, EIGEN-6C4, GECO, SGG-UGM-1 and XGM2019e_2159 gravitational models. We also stochastically evaluated the performance of these GGMs by computing their Root-Mean-Square (RMS) fit with ground-based gravity measurements. The results show that the EIGEN-6C4 and XGM2019e_2159 models have the best RMS fit with the ground-based gravity data. A spatial pattern in Bouguer gravity maps (compiled using these two models) generally closely agrees with a geological configuration of the basins, while also exhibiting some more detailed geological features. Interestingly, however, despite the XGM2019e has the best fit and better mimics major geological features, the gravity image from this model does not exhibit a sediment signature in a portion of the Afikpo basin. A possible reason is that the topographic information used to recover a higher-frequency gravity spectrum of this model might suppress a gravitational signature of subsurface density structures. A comprehensive interpretation of geological features thus requires a careful analysis of existing GGMs, terrestrial gravity data as well as all other reliable geological and geophysical information.

The Identification of Impact Craters from GRAIL-Acquired Gravity Data by U-Net Architecture

The identification of impact craters on the Moon and other planetary bodies is of great significance to studying and constraining the dynamical process and evolution of the Solar System. Traditionally, this has been performed through the visual examination of images. Due to the effect of overburden, some structural features cannot be effectively identified from optical images, resulting in limitations in the scope, efficiency and accuracy of identification. In this paper, we investigate the viability of convolutional neural networks (CNNs) to perform the detection of impact craters from GRAIL-acquired gravity data. The ideal values of each hyperparameter in U-net architecture are determined after dozens of iterations of model training, testing and evaluation. The final model was evaluated by the Loss function with the low value of 0.04, indicating that the predicted output of the model reached a relatively high fitting degree with the prior labelled output. The comparative results with different methods show that the proposed method has a clear detection of the target features, with an accuracy of more than 80%. In addition, the detection results of the whole image account for 83% of the number of manually delineated gravity anomalies. The proposed method can still achieve the same quality for the identification of the gravity anomalies caused by impact craters under the condition that the resolution of GRAIL gravity data are not superior. Our results demonstrate that the U-net architecture can be a very effective tool for the rapid and automatic identification of impact craters from gravity map on the Moon, as well as other Solar System bodies.

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.

Sub-surface Geological Modeling Based on Gravity Residual Data in Adang Volcanic Rock Area, Mamuju, West Sulawesi Province

The Mamuju area of West Sulawesi Province is composed of Adang volcanic rock that is a product of the process of volcanism in a volcanic complex with an eruption center and several lava domes. The geology of the study area is composed of eleven rock units, namely Adang breccia, Adang lava, lava dome, volcanic conglomerate, Ampalas breccia, Malunda breccia, Boteng lava, Tapalang breccia, limestone, reef limestone, and alluvium. The mineralization of uranium, thorium, and rare earth elements formed in Adang lava thorianite veins. Adang lava is intruded by a dioritoid found in the Mamuju river upstream. The gravity modeling technique has produced two 2-D subsurface models based on gravity data on 2-D cross-sections of the residual gravity map. It is known that the rock density range from 2.10 to 2.85 g/cm3 in the study area. Based on the interpretation of two 2-D subsurface models, a batholith, a giant-sized intrusive rock, is found in the southeastern part of the study area with a rock density of about 2.85 g/cm3 and is interpreted to be dioritoids. Furthermore, deep intrusion rocks also occur in the center part of the study area with a rock density of 2.8 g/cm3. It is estimated to be the same as the rock in the southeastern part of the study area. Dioritoid intrudes a volcanic breccia sedimentary rock with a density of about 2.1 g/cm3.

Gravity study of the Western Bahira Basin and the Gantour Phosphatic Plateau, central Morocco: Interpretation and hydrogeological implications

The Western Bahira Basin (WBB), located in Central Morocco, is known for its large reserves of phosphate, which are currently being extracted through open pit mines within the Gantour Phosphatic Plateau (GPP). This mining activity, as well as the increasing agricultural development that this region has been experiencing during the last few decades, has subjected the groundwater in this semi-arid region to intense exploitation through pumping. Consequently, thorough knowledge of the underground water resources is essential for sustained activity.This study uses gravity data to investigate the deep geologic structure of the western Bahira and Gantour plateau area. Its main purpose is to improve the knowledge of this structure that influences the groundwater dynamics.The methodology involves, in addition to the qualitative and quantitative interpretation of the gravity data, the use of various filtering and analysis techniques to highlight the major geological structures. In fact, a qualitative analysis of the residual gravity map shows that the observed anomalies can be explained in terms of the bedrock topography of the study area. Positive anomalies spatially correlate with the outcrops of this bedrock in the Hercynian massifs of Jebilet and Rehamna, as well as with the Douar Rhirat structural high. The negative anomalies, on the other hand, tend to reflect increased thicknesses of sedimentary sequences, such as in the southern part of the WBB. Moreover, the Brikyine granite in the north of the study area is noticeably associated with the highest amplitude negative anomaly.Analysis of the residual gravity data using the total horizontal gradient, upward continuation, and Euler deconvolution techniques provides a quantitative assessment of the geologic structure. These methods help delineate various structures oriented in two main directions: N45E and N105E. Among these structures, several major faults have been identified. They are rooted at a maximum depth in excess of 2800 m. These faults are responsible for the general structure of the study area and the morphology of the basement.Furthermore, the 2D forward modeling, performed across the main negative gravity anomalies of the WBB, helps characterize the Paleozoic bedrock topography and provides more constraints on its variation. The resultant gravity models clearly show an asymmetric structure for the western Bahira trough. This depression is filled by sedimentary formations whose thickness at the depot-center can locally reach 1200 m. Additional analysis of piezometric data shows that the groundwater flows are controlled by the gravity structures highlighted in this study.

Crustal architecture of the Eastern Ghats Mobile Belt and tectonic implications: Constraints from aeromagnetic, gravity and geological data

We present a joint interpretation of the aeromagnetic and gravity anomaly datasets of the Precambrian Eastern Ghats Mobile Belt, eastern India, to delineate the detailed crustal architecture, identify faults and shear zones, as well as boundaries of different terranes throughout this belt. We use geological constrained analysis of the distinct aeromagnetic anomaly signatures to re-interpret the extent of the Jeypore, Krishna, Eastern Ghats, and Rengali Provinces. Forward modelling of paired gravity anomalies and an increase in magnetic response along the craton-mobile belt boundary reveal that it is dominated by high-density and highly magnetic granulite facies rocks that overthrust the low-density and low magnetic older cratonic gneissic rocks along the deep crustal faults, suggesting the Eastern Ghats Mobile Belt terranes are allochthonous in nature. Two high magnetic anomaly belts in the Krishna and Eastern Ghats Provinces define a terrane-scale fold (orocline). The younger normal faults of Godavari Basin overprint the charnockitic belt in the southern part of the Eastern Ghats Province, suggesting that these high magnetic belts pre-date the Pan-African Orogeny. The boundary between the Eastern Ghats Province and Krishna Province is identified by the change in anomalies in magnetic and gravity maps. The Sileru Shear Zone and Kerajung Shear Zone separates the Eastern Ghats Province-Jeypore Province and Eastern Ghats Province-Rengali Province respectively, are characterized by a sharp change in magnetic anomalies. The intra-province Nagavali-Vamsadhara Shear Zone and Mahanadi Shear Zone are characterized by subdued magnetic anomalies. Inversion of the regional gravity anomalies revealed that the Moho is slightly shallower (~5 km) beneath the Eastern Ghats Mobile Belt compared to the neighbouring Cratons.