Detailed Geological Interpretation Research Articles

Fold-thrust belt in the southern front of the central High Atlas (Morocco): Analysis and implications for the tectonic inversion of the atlas system

Thrust folds have developed significantly in the meso-Cenozoic rock units of the Errachidia-Boudnib basin. The study areas correspond to the north part of the Pre-African Trough, which is located between the Anti-Atlas and the Atlas systems. It is characterized by faulted anticlines that are indicative of a foreland orogenic context.The Atlas system's structural evolution underwent several stages, starting with a Triassic extensional event followed by a period of fault reactivation during the Atlas compression. This research focuses on examining the thrust and detachment folds associated with both reverse and strike-slip components. For this purpose, we performed detailed geological mapping and interpretation of folding and fault slip data.As a result of shortening, field observations reveal that the study area exhibited well-developed thrusting geometry. Preexisting blind faults and multiple decollement levels within favorable formations such as Cenomanian evaporitic marls, Cenomanian-Turonian marls rich in organic matter, and Senonian argillites influence the folding patterns, which are not uniform. The findings demonstrate two key points. First, the most significant folds have formed along major blind thrusts. Subsequently, between these major faults, detachment folds were developed within the Jurassic-Cretaceous strata. Currently, due to erosion, certain thrusts have become visible, including the Ta'bbast thrust fault, Ait Atman (from the first stage), and the Timazguit fault zone (from the second stage). The South Atlas fault largely remains a blind fault. Additionally, the study emphasizes the presence of strike-slip components and en-echelon folding, indicating a transpressional regime during the uplift of the Atlas system.

Spatial Correlations between the Terrain Features, Gravitational Field and Seismic Velocity Anomalies in the Central Kamchatka Region

Abstract ––Different approaches to tectonic zoning and different types (complexes) of used data, on the basis of which the zoning is performed, are the plurality of tectonic schemes of Kamchatka and the Kamchatka region previously obtained by different authors. In this work, a joint analysis of gravity field anomalies, gravity field and relief transforms, magnetic field and modern seismotomographic models of velocity anomalies was used to study spatial relationships of tectonic manifestations of geological processes. As a result of this study, a linear-block type tectonic scheme was constructed. The obtained linear structural elements are in good agreement with the data of potential fields, seismic constructions and previously published materials. The productivity of the presented method of complex analysis of geophysical fields for revealing their spatial relations and block structures of the environment is shown. The analysis outcomes can be used to establish spatial constraints for gravity field sources when solving inverse problems, potential field separation problems and their detailed geological interpretation.

Unravelling rift propagation from Cenozoic subsidence patterns: Examples from the Dangerous Grounds, South China Sea

AbstractHow seafloor spreading in marginal basins controls subsidence patterns in continental margins under rift propagation settings remains poorly understood. Herein, based on detailed geological interpretation and backstripping of 37 high‐resolution multichannel seismic reflection sections, we calculate the Cenozoic tectonic subsidence across the Dangerous Grounds (DG), South China Sea, in order to study interactions between seafloor spreading and the propagation of rift basins. Our results show that rapid subsidence occurred in the eastern Dangerous Grounds (EDG) from the Palaeocene to early Oligocene, then migrated westwards to the middle Dangerous Grounds (MDG) during the early Oligocene to early Miocene, and finally reached the western Dangerous Grounds (WDG) during the early to middle Miocene. We interpret this western migration of intensive subsidence as the response of the inherited pre‐Cenozoic heterogeneous lithospheric structure of South China. Thermal re‐equilibration of the lithosphere then dominated the rapid post‐spreading subsidence throughout the whole DG from the middle Miocene. An anomalous subsidence deficit occurred in the EDG during the early Oligocene to early Miocene, and in the MDG during the early to middle Miocene; this phenomenon might be related to small‐scale mantle convection associated with the propagation of seafloor spreading from east to southwest.

Geology of giant quartz veins and their host rocks from the Eastern Pyrenees (Southwest Europe)

ABSTRACT Giant Quartz Veins (GQVs) are ubiquitous in different tectonic settings and, besides being often related to hydrothermal ore deposits, also represent large-scale fingerprints of the structural and geochemical history of the rocks in which they are hosted. Here we present detailed geological maps and interpretations of three key areas of the Eastern Pyrenees where GQVs are well exposed. The studied rocks record different styles of deformation and are representative of common settings of the Pyrenees where GQVs are present: pre-Variscan metasedimentary and metavolcanic rocks, late Variscan granitoids, and Mesozoic and Cenozoic sedimentary rocks. GQVs in the study areas formed along pre-existing brittle and ductile structures or at locations with lithological heterogeneities, and have alteration haloes of silicified host rocks. The geological maps and interpretations presented here contribute to gain insights into the formation mechanisms of GQVs and into the structural constraints on fluid flow and mineral reactions at different depths of the Earth’s crust.

Time Constraints of Late Cenozoic Tectonic Deformation of the Atushi Anticline, Southwestern Tian Shan: Evidence From Cosmogenic Nuclide Burial Age

With the latest uplift episode of Tian Shan occurring since early Miocene, a series of thrust–fold belts were formed in front of Tian Shan. The Kashi foreland thrust–fold belt (KFTB) provided a unique case to understand the ongoing intracontinental deformation within the Pamir–Tian Shan convergence zone (PTCZ). Previous cosmogenic nuclide chronological studies on growth folds suggested that the young thrust–fold belt in front of Pamir formed during 6–1.07 Ma. However, the age constraints of late Cenozoic deformation in front of southwestern Tian Shan are still debated. In this study, we attempt to constrain the initial deformation time of the NEE-striking Atushi anticline (ATA) in the KFTB through the cosmogenic nuclide burial dating data of growth strata near the boundary between Pliocene–Pleistocene Atushi Formation and Xiyu Formation (Xiyu Conglomerate), which are exposed in the southern limb of ATA. Moreover, detailed geological interpretations of multiple remote sensing images and field investigations are also carried out to document the late Cenozoic structural deformation and geomorphologic features of ATA. The 26Al/10Be burial dating data of four fine-grained samples reveal that the syntectonic deposit of ATA initiated at 1.79 ± 0.16 Ma, and the deposit of Xiyu Conglomerate started since 1.67 ± 0.18 Ma. Thus, we suggest that the thrust–folding of ATA began at ca.1.79 Ma and is currently still active.

Monitoring Dynamic Changes in Reservoir Production Using Time-Lapse Walkaway Das-Vsp Data

With the rapid development of optical fibre sensing in recent years, Distributed Acoustic Sensing (DAS) is gradually considered as a viable alternative to borehole geophone arrays for the acquisition of borehole seismic or Vertical Seismic Profile (VSP) data. The data collected by an optical cable permanently deployed behind casing have a high degree of consistency and high SRN, which is less affected by receiving factors such as the cable coupling issues and the tube wave. This paper describes the time-lapse Walkaway DAS-VSP data acquisition in Dagang Oilfield of China and the multi-stage time-lapse Walkaway DAS-VSP data consistency processing procedures. Through the fine imaging processing of multi-stage Walkaway DAS-VSP data and detailed geological interpretation, it is possible to identify and map the range of fluid migration around the wellbore due to production, perform cross-validation during the monitoring period using the borehole oil production statistics information, and analyse the dynamic changes of reservoir fluids within the monitoring field. The Walkaway DAS-VSP survey has become an important development of the borehole seismic technique due to its advantages of high density, high efficiency, low cost and good consistency, which can be carried out with repeated observations and also for permanent monitoring. Therefore, the use of time-lapse Walkaway DAS-VSP surveys is proposed for the monitoring of oil and gas production in mature fields. The repeated time-lapse Walkaway DAS-VSP surveys can provide high-quality borehole seismic data for the study of dynamic changes of the reservoir fluid around the wellbore to a certain range. The key points of this paper mainly include: (1) Time-lapse Walkaway DAS-VSP data acquisition; (2) Special time-lapse Walkaway DAS-VSP data processing procedures; (3) Time-lapse Walkaway DAS-VSP data inversion; (4) Map reservoir fluid dynamic changes during the oil and gas production. In the application process of the time-lapse Walkaway DAS-VSP, the high-accuracy velocity fields, high-resolution structure imaging and multiple attribute inversion of the reservoir formation around the wellbore have been obtained. In addition, it also provides reservoir fluid identification and mapping based on high-accuracy Walkaway DAS-VSP and surface seismic data, which provide a basis for the establishment of multi-domain and multi-dimensional geological and reservoir models.

Detachment-controlled subsidence pattern at hyper-extended passive margin: Insights from backstripping modelling of the Baiyun Rift, northern South China Sea

How detachment fault controls the basin subsidence at hyper-extended passive margin remains mysterious. Based on a detailed geological interpretation and backstripping on 29 high-resolution multi-channel seismic profiles, we calculate the basin-scale tectonic subsidence across the Baiyun Rift to study the relationship between tectonic subsidence and detachment faulting. Our results confirm that detachment faulting is the primary factor controlling the syn-rift subsidence. A decaying subsidence rate, or deficit subsidence is observed in the eastern Baiyun Rift from the early to late Eocene, which is in marked contrast to the intensive brittle stretching. We attribute this to the doming of the detachment fault footwall involving the syn-rift magmatism during its hyper-extension process. While in the western Baiyun Rift the average subsidence rate is over 45 m Myr−1 higher than that in the eastern as the response of flexural loading in the late Eocene. During the post-rift stage, the subsidence rate shows a similar oceanward increasing trend, and an anomalous rapid subsidence event during the middle Miocene in the eastern Baiyun Rift, which can be ascribed to the magma-assisted weakened rheological condition of the lithosphere deriving from the syn-rift detachment faulting. We propose that this relationship between subsidence pattern and detachment faulting has global applicability for other hyper-extended rift systems developing detachments and magmatic-related dome structures.

Modern problems and prospects for the development of magnetotelluric monitoring on the territory of the Bishkek geodynamic test site

The high sensitivity of the electromagnetic parameters of the geological environment to the influence of geodynamic processes for the territory of the Bishkek geodynamic test site is shown. An assessment of the characteristics of the stress-strain state of the geological environment and the behavior of variations in electromagnetic parameters has been carried out in order to identify patterns in their relationship for seismically active regions of the Tien Shan. The promising objects for monitoring observations are identified and the results obtained are presented. The experimental results obtained indicate that the position of the regions of stable correlation (clusters) on the polar correlation diagrams is associated with the geoelectric structure of the observation point and corresponds to the orientation of the main tectonic elements in the vicinity of this point. A detailed geological and geophysical interpretation of geoelectric sections was carried out in order to separate modern active faults and weakened zones of the Earth’s crust, for example, the Kochkor basin. The relationship between the manifestation of geoelectric inhomogeneities and the spatial distribution of the epicenters of seismic events is revealed; it is shown that a significant part of earthquake epicenters is confined to structural inhomogeneities of the Earth’s crust; the depths of the geoelectric section, most sensitive to the influence of geodynamic processes, have been determined. The behavior of variations in the electrical conductivity of the earth‘s crust in a wide range of periods has been investigated according to the data of profile magnetotelluric soundings (MTS) at the Kentor geophysical monitoring minipolygon. Field experiments confirm the concept of the relationship between the stress-strain state of the medium and the change in apparent resistivity through the redistribution of saline solutions between fracture systems. The problems and trends in the development of magnetotelluric monitoring of modern geodynamic processes in the Northern Tien Shan are shown. To solve the tasks set, a methodology for conducting monitoring studies is proposed, which most fully takes into account the specific features of the deep structure and distribution of seismicity of the Bishkek geodynamic test site.

A local lithospheric structure model for Vietnam derived from a high-resolution gravimetric geoid

High-resolution Moho and lithosphere–asthenosphere boundary depth models for Vietnam and its surrounding areas are determined based on a recently released geoid model constructed from surface and satellite gravity data (GEOID_LSC_C model) and on 3ʹʹ resolution topography data (mixed SRTM model). A linear density gradient for the crust and a temperature-dependent density for the lithospheric mantle were used to determine the lithospheric structure under the assumption of local isostasy. In a first step, the impact of correcting elevation data from sedimentary basins to estimate Moho depth has been evaluated using CRUST1.0 model. Results obtained from a test area where seismic data are available, which demonstrated that the sedimentary effect should be considered before the inversion process. The geoid height and elevation-corrected sedimentary layer were filtered to remove signals originating below the lithosphere. The resulting Moho and lithosphere–asthenosphere boundary depth models computed at 1ʹ resolution were evaluated against seismic data as well as global and local lithospheric models available in the study region. These comparisons indicate a consistency of our Moho depth estimation with the seismic data within 1.5 km in standard deviation for the whole Vietnam. This new Moho depth model for the study region represents a significant improvement over the global models CRUST1.0 and GEMMA, which have standard deviations of 3.2 and 3.3 km, respectively, when compared to the seismic data. Even if a detailed geological interpretation of the results is out of scope of this paper, a joint analysis of the obtained models with the high-resolution Bouguer gravity anomaly is finally discussed in terms of the main geological patterns of the study region. The high resolution of our Moho and lithosphere–asthenosphere boundary depth models contribute to better constrain the lithospheric structure as well as tectonic and geodynamic processes of this region. The differences in Moho depth visible in the northeast and southwest sides of the Red River Fault Zone confirmed that the Red River Fault Zone may be considered the boundary between two continental blocks: South China and Indochina blocks. However, no remarkable differences in lithosphere–asthenosphere boundary depth were obtained from our results. This suggests that the Red River Fault Zone developed within the crust and remained a crustal fault.

Revisiting an old profile: an updated geoarchaeological study at Nasera Rockshelter (Tanzania)

ABSTRACTNasera Rockshelter hosts a highly continuous sedimentary record, containing a wide array of archaeological remains from Middle Stone Age, Later Stone Age and Pastoralist occupations. Excavated by L. Leakey and M. Mehlman, geological studies carried out by R. Hay included granulometric and general mineralogical analyses but lacked individualized, detailed description and interpretation of each of the 25 levels exposed. This study presents updated detailed geological descriptions and interpretations of 17 levels exposed during excavations in 2018.

Challenges in the use of potential field data for studies of remote, deep-water frontier basins

Given the sparsity of seismic data covering remote offshore frontier basins, Geoscience Australia?s studies of these areas rely heavily on gravity and magnetic data. These data complement 2D seismic reflection data by allowing interpretations to be extrapolated away from the generally widely-spaced seismic lines. However, interpreting potential-field data in frontier areas is challenging. Continuous gravity coverage is only available from satellite-altimetry-derived data, but the resolution of these data is often not sufficient for detailed geological interpretation and the data are subject to error in areas of shallow water or close to the coastline. Shipborne data provide higher-resolution data along track, but the sparsity of ship-tracks means that line levelling is difficult. Modelling gravity data to test seismic interpretations of sediment thickness is further complicated by poor constraints on the depth to the Moho. Efforts to understand frontier basins could be improved with better knowledge of the Moho (e.g. from seismic refraction data) and by better ship-track coverage. Extensive acquisition of airborne gravity and magnetic data over Australia?s margins would also provide better coverage and provide a seamless link between offshore and onshore areas.

Field Geology and Structures of Migmatitic Gneisses Around Ibillo-Okene Area, Southwest Nigeria

Ibillo-Okene migmatites are a typical example of the Basement Complex rocks of southwest Nigerian, which is part of the larger West African shield. They lie directly north and constitute the northern closure of the Igarra Schist Belt. They are interbanded with relics of metasedimentary units called older metasediments as well as overlain by younger metasediments. These units are affected by co-genetic or similar episodes of deformation that has both petrogenetic and economic significance as observed in Igarra Belt south of this area. Though this area is interesting in terms of geology and tectonic setting, detailed geological and structural interpretation of features in the area is lacking due to limited accessibility. Land Sat 8 and shuttle radar topographic mission (SRTM), data constitute useful tools for preliminary reconnaissance survey as well as structural interpretation. Based image interpretation, a minimum of three deformation events were identified: The first event (D1) which is essentially a ductile deformation produced foliations and isoclinal folds which are axial planar such that both the eastern and western limbs of the folds are parallel with regional metamorphic foliation trend S1 (NNW-SSE) and dominant lineament trends (ENE-WSW). The second event (D2) is believed to have produced a progressive reactivation of the D1 event with accentuation of the E-W compression leading to folding of the axes of F1 folds. The third event (D3) has two deformational stages: a ductile deformation at the onset at a higher temperature and pressure and a brittle deformation at the later stages with lower temperature and pressure. Geologic fieldwork which was further conducted to validate structures and units identified from image processing revealed that the migmatites are essentially metatexites which to the northwest is dialational, dialational net-structured in the northeast and straumatic in the southeast. The southwest of the area constitute the basinal closure of the Igarra area overlain by relics of the metasedimentary units. This research underscore the relevance of remotely sensed data in geological investigation whose results have important implications in terms of regional tectonics and geological mapping as well as in land-use planning and other areas such as hydrogeology or geotechnics. Keywords: Migmatite, Ibillo, Okene, metasediments, Remote sensing. DOI : 10.7176/JEES/9-2-08

Understanding Geology and Structure: An Essential Part of Mineral Resource Estimation

The assumption of continuity of mineralisation between sampling points, as stated in the JORC Code, requires a “confident interpretation of the geological framework”. The elements of relevance to a geological framework vary greatly depending on th e commodity and style of mineralisation. In general terms, at least two elements must be considered to underpin a geological framework: space and time.The geometry and location of a mineralised body are controlled by physical and/or chemical elements, which can be unravelled by detailed geological mapping, adequate geochemical (including a quality analysis-quality control program) and structural interpretations, and by 3D geological modelling. These elements may involve, among other, aspects of stratigraphy, chemical or physical properties of the rocks (e.g. texture, grain size) and structural features such as faults, fractures and folds.Mineralisation events that lead to economic deposits are often relatively short-lived periods of focused fluid transfer and element-exchange, which result in mobilisation and deposition of metals in well-defined areas. Understanding the temporal framework and interaction of structural elements and mineralising events (determining genetic relationships, e.g. pre-, syn- and post-mineralisation) results in the development of more accurate geological models and can lead to predictive capabilities and new discoveries.We present case studies in regional metamorphic, igneous, sedimentary and surficial geological environments, demonstrating how understanding the mineralisation system not only results in increased confidence in the resource, but also facilitates reduction of exploration risks.

High‐resolution reflection seismics reveal the structure and the evolution of the Quaternary glacial Tannwald Basin

ABSTRACTOver‐deepened basins exist throughout the Alpine realm. Improving our knowledge on these basins is of high social relevance, since these areas are often well‐populated and they possess, for instance, unusual hydrological settings. Nonetheless, geophysical and sedimentological investigations of over‐deepened basins are rare. We analyse the sedimentary succession of such a basin, the Tannwald Basin, through geological interpretation of seismic reflection profiles. The basin is located approximately 60 km north of the European Alps. It was incised into Tertiary molasse sediments by the Rhine Glacier and later filled by glacial, fluvial, and lacustrine deposits of 250 m thickness. The Leibniz Institute for Applied Geophysics acquired a grid of five high‐resolution seismic reflection lines that imaged till the deepest parts of the Tannwald Basin. The seismic profiles, processed to a pre‐stack depth migration level, allow a detailed geological interpretation that is calibrated with the help of a nearby borehole. We determine the structure and the seismic facies of the sediment succession in the basin and presume the following hypothesis of the evolution of the basin: sub‐glacial erosion comprises the excavation of the over‐deepened basin as well as detachment of large fragments of molasse material. These molasse slabs were deposited within the basin in a layer of basal till that graded upwards in water‐lain till and fine‐grained deposits. During the last two glaciations, the basinal structure became buried by till sequences and glacio‐fluvial sediments.

ON METHODOLOGY OF TEACHING GEOPHYSICAL COURSES AT THE INSTITUTE OF EARTH SCIENCES, SFU

The results of the works undertaken by students on practical classes and during educational practices have been discussed. Causes and difficulties in student learning of exploratory geophysics have been analyzed. It has been found a deficiency in practical skills of future engineers relevant to the work with geophysical facilities and equipment and further mental processing of the measured parameters of natural and artificial geophysical fields. A brief description has been given for improvements in the methodology of teaching geophysics to future geology and geoecology engineers via inclusion of practical works with geophysical equipment on the test site on the Zorge Street with tasks linked to engineering-geological cross-section study and mapping underground infrastructure on the given area. There are some other examples of student involvement in solution of geophysical tasks on the objects of educational geophysical practices with subsequent detailed geological and geophysical interpretation.

A-DInSAR Monitoring of Landslide and Subsidence Activity: A Case of Urban Damage in Arcos de la Frontera, Spain

Terrain surface displacements at a site can be induced by more than one geological process. In this work, we use advanced differential interferometry SAR (A-DInSAR) to measure ground deformation in Arcos de la Frontera (SW Spain), where severe damages related to landslide activity and subsidence have occurred in recent years. The damages are concentrated in two residential neighborhoods constructed between 2001 and 2006. One of the neighborhoods, called La Verbena, is located at the head of an active retrogressive landslide that has an extension of around 0.17 × 106 m2 and developed in weathered clayey soils. Landslide motion has caused building deterioration since they were constructed. After a heavy rainfall period in winter 2009–2010, the movement was accelerated, worsening the situation. The other neighborhood, Pueblos Blancos, was built over a poorly compacted artificial filling undergoing a spatially variable consolidation process which has also led to severe damage to buildings. For both cases, a short set of C-band data from the “ENVISAT 2010+” project has been used to monitor surface displacement for the period spanning April 2011–January 2012. In this work we characterize the mechanism of both ground deformation processes using in situ and remote sensing techniques along with a detailed geological interpretation and urban damage distribution.

Litho-structural analysis of eastern part of Ilesha schist belt, Southwestern Nigeria

The Ilesha schist belt is an excellent example of high strain shear belt within basement complex of southwestern Nigeria which is part of the larger West African Shield. The Ilesha schist belt is characterised by metasediment-metavolcanic, migmatite-gneiss and older granite rocks and the occurrence of a Shear zone which has been traced to and correlated with the central Hoggar Neoproterozoic shear zone as part of the Trans-Saharan Belt. Although the area is interesting in terms of geologic-tectonic setting, however, detailed geological assessment and structural interpretation of features in this area is lacking due accessibility problem.For these reasons we applied principal component analysis (PCA) and band ratio (BR) techniques on Landsat 8 OLI data for lithological discrimination while for structural interpretation, filtering techniques of edge enhancement and edge detection was applied on digital elevation model (DEM) acquired by shuttle radar topographic mission (SRTM) sensor. The PCA outperform BR for discrimination between quartzite and granite which are the most exposed rock units in the area. For structural interpretation, DEM was used to generate shaded relief model and edge maps which enable detailed structural interpretation. Geologic fieldwork was further conducted to validate structures and units identified from image processing. Based image interpretation, three deformation events were identified. The first event (D1) which is majorly a ductile deformation produced foliations and folds whose axial planes trend in NNE-SSW. The second event (D2) resulted in reactivation and rotation of the D1 structures particularly the folds in the NE-SW. The third event (D3) produced a transgressive deformation starting with the ductile deformation resulting in the development of sigmoidal structures oriented in NE-SW to E-W direction and the brittle deformation occurring at later stages producing fractures oriented in the E-W to NE-SW directions.These results have important implications in terms of regional tectonics and geological mapping as well as in land-use planning and other areas such as hydrogeology or geotechnics.

K-Means Cluster for Seismicity Partitioning and Geological Structure Interpretation, with Application to the Yongshaba Mine (China)

Seismicity partitioning is an important step in geological structure interpretation and seismic hazard assessment. In this paper, seismic event location (X,Y,Z) and Euclidean distance were selected as the K-Means cluster, the Gaussian mixture model (GMM), and the self-organizing maps (SOM) input features and cluster determination measurement, respectively, and 1516 seismic events (M>-1.5) obtained from the Yongshaba mine (China) were chosen for the cluster analysis. In addition, a Silhouette and Krzanowski-Lai- (KL-) combined S-KL index was proposed to obtain the possible optimum cluster number and to compare the cluster methods. Results show that the K-Means cluster obtains the best cluster “quality” with higher S-KL indexes on the whole and meaningful clusters. Furthermore, the optimal number for detailed geological structure interpretation is confirmed as eleven clusters, and we found that two areas probably have faults or caves, and two faults may be falsely inferred by mine geologists. Seismic hazard assessment shows that C5 and C7 (K=11) have a high mean moment magnitude (mM) and C1, C2, C3, and C4 (K=11) have a relatively high mM, where special attention is needed when mining. In addition, C7 (K=11) is the most shear-related area with a mean S-wave to P-wave energy ratio (mEs/Ep) of 41.21. In conclusion, the K-Means cluster provides an effective way for mine seismicity partitioning, geological structure interpretation, and seismic hazard assessment.

Magnetic Theory and Applications in the Naples Bay (Southern Tyrrhenian Sea, Italy): Magnetic Anomaly Fields and Relationships with Morpho-Structural Lineaments

Magnetic theory and application to a complex volcanic area located in Southern Italy are here discussed showing the example of the Gulf of Naples, located at Southern Italy Tyrrhenian margin. A magnetic anomaly map of the Gulf of Naples has been constructed aimed at highlighting new knowledge on geophysics and volcanology of this area of the Eastern Tyrrhenian margin, characterized by a complex geophysical setting, strongly depending on sea bottom topography. The theoretical aspects of marine magnetometry and multibeam bathymetry have been discussed. Magnetic data processing included the correction of the data for the diurnal variation, the correction of the data for the offset and the leveling of the data as a function of the correction at the cross-points of the navigation lines. Multibeam and single-beam bathymetric data processing has been considered. Magnetic anomaly fields in the Naples Bay have been discussed through a detailed geological interpretation and correlated with main morpho-structural features recognized through morpho- bathymetric interpretation. Details of magnetic anomalies have been selected, represented and correlated with significant seismic profiles, recorded on the same navigation lines of magnetometry. They include the continental shelf offshore the Somma-Vesuvius volcanic complex, the outer shelf of the Gulf of Pozzuoli offshore the Phlegrean Fields volcanic complex, the relict volcanic banks of Pentapalummo, Nisida and Miseno, the Gaia volcanic bank on the Naples slope, the western slope of the Dohrn canyon, the Magnaghi canyon’s head and the magnetic anomalies among the Ischia and Procida islands.

Magnetic Basement Depth Re-Evaluation of Naraguta and Environs North Central Nigeria, Using 3-D Euler Deconvolution

This paper presents a detailed geological interpretation of the aeromagnetic data over Naraguta and environs using 2-D spectral inversion and 3-D Euler deconvolution techniques. The objectives of the study are to re-evaluate the depth to the magnetic basement and to delineate associated structural features in the study area. Data enhancement was carried out to separate residual features relative to the strong regional gradients and the more intense anomalies due to basement features and igneous intrusives. Results of the 2-D spectral analysis revealed a two layer depth source model. The deeper magnetic source bodies (d<SUB>2</SUB>) varies from 1.672km to 2.3km with an average depth of 1.999km while the depth to the shallower magnetic source bodies (d<SUB>1</SUB>) ranges from 0.55km to 0.897km with an average depth of 0.711km. The shallower magnetic anomalies are believed to be as the result of basement rocks which intruded into the sedimentary rocks while the deeper layer may be attributed to magnetic basement surface and intra-basement discontinuities like faults, fractures and lineations. Structural analysis of these shallow anomalies using 3-D Euler deconvolution with structural index values ranging from 0-3, revealed three main structural models which include spheres, horizontal pipes/cylinders and sills/ dikes. Similarly, magnetic basement depth estimates using 3-D Euler deconvolution revealed a magnetic basement depth range of 0.5 - 2.5km. Finally, the average sedimentary thickness of 1.999km estimated from the study area is unfavorable for hydrocarbon generation and accumulation. However, the area is more viable for solid mineral exploitation based on the presence of several intrusive and linear features which may have acted as conduits for mineralization.