Geophysical Results Research Articles

Voluminous Paleogene volcanism in the southern Mesa Central, Mexico: Unravelling the fissure-fed origin of rhyolitic ignimbrites of the Villa Garcia-Loreto Volcanic Complex

The southern portion of the Mesa Central (MC) physiographic province is covered by numerous Oligocene to Miocene volcanic successions that are part of the Sierra Madre Occidental silicic large igneous province. The MC merges with the Sierra Madre Occidental and the southern Basin and Range extensional province. The voluminous Villa Garcia-Loreto Volcanic Complex (VGLVC) is located in the southern portion of the MC and consists of predominantly rhyolitic lava flows, and voluminous products of explosive rhyolitic volcanism, mainly as lava-like to rheomorphic ignimbrite sheets. The volcanism in the area appears in two events, first, at 60.4 ± 0.3 Ma (K–Ar whole-rock age) with the fissure-fed eruption of an andesitic lava and second, with the fissure-fed eruption of two densely-welded, crystal-poor ignimbrites at 31.59 ± 0.14 Ma and 28.66 ± 0.07 Ma (40Ar–39Ar sanidine ages). Chondrite-normalized rare earth element patterns and primitive mantle normalized multi-element patterns show enrichment in light rare earth elements (LREE) and high field strength elements (HFSE). Geochemical analysis and mineral chemistry show that the andesitic magmas were generated by partial melting of the uppermost mantle in a subduction-related setting and ascended directly through the brittle crust and erupted along N-S trending faults. Rhyolitic magmas were generated by partial melting of the lower crust in an intra-plate and extensional setting, associated with an intense phase of the southern Basin and Range extension. During the ascent and storage in a shallow magma chamber fractional crystallization of mainly feldspars and pyroxene was the major process taking place in the evolution of the magma. Geophysical results suggest that the volcanic rocks of the VGLVC were originated by fissure-fed eruptions associated with the Loreto Graben fault. The major Basin and Range faults locally reach a depth of 7 km and trending in NNW-SSE direction. The combined results show that the Basin and Range extension favored the formation, ascent, and eruption of rhyolitic and andesitic magmas in the southern MC.

Integrated geophysical approach in exploration of iron ore deposits in the North-eastern Aswan-Egypt: a case study

The mines of magnetite and hematite occupy some areas of the Eastern Desert at Wadi Abu Subeira, northeast of Aswan city which is a volcanic and tectonic area. It is one of the largest arc sedimentary rock sequence affected by faulting and folding due to repeated stages of deformation. The iron deposits in this area are of oolitic type and exist in two bands inter-bedded with ferruginous sandstone and clay layers. The thickness of the bands varies from 0.5 to 3.5 m. Detailed geophysical work has been carried out on the promise site of Abu Subeira to identify the lateral and vertical distribution of the iron-ore deposits at this area. Many geophysical methods were applied in this study including Land Magnetic Survey, Electrical Resistivity Imaging (ERI), Induced Polarization (IP), and Time-Domain Electromagnetic (TDEM). Besides, rock samples from the iron ores were collected for chemical analysis. The X-ray fluorescence (XRF) and X-ray diffraction (XRD) techniques were applied for estimation of iron concentration (Fe %) and other minerals’ contents in the rock samples. The field data sets were measured along the iron ore bodies of Wadi Abu Subeira and were processed and analyzed by the proper software packages. The areas with iron ore deposits were expressed in the geophysical results by low resistivity, high chargeability, and moderate to high magnetic anomalies. Integrated interpretation of the obtained results revealed that the ore deposits exist in the form of lenses with variable thickness ranging from few meters to about 30-m thick. The mineral occurrences in Abu Subeira are managed by the major faults and the hydrothermal fluids flowing along these faults.

The geometry, sedimentary filling and depth estimate of the Mirandiba Basin, Pernambuco, Brazil: new insights about the depositional regional gap of rift phases in the interior basins

The Mirandiba Basin has a well-defined stratigraphic sequence and its sedimentation may be directly correlated with the Jatoba Basin and some other interior basins. The sedimentation began in intracratonic conditions with a Paleozoic sequence (Tacaratu/Inaja Formations), which acted as a substrate without any genetic relationship with the basin. The fluvial Tacaratu Formation emerges beyond the limits of this basin, where a remnant core named here as Poco do Ico was found wrapped around the basement to the west of the basin. Subsequently, there was a deposition in a shallow marine environment of the Inaja Formation (Devonian) formed by the intercalation of clay/siltstones and sandstones with ichnofossils. Pre-rift sedimentation occurs over the Paleozoic sequence, characterized in the basin by the lacustrine sediments of the Alianca Formation, represented by the intercalation of shales and calcarenites with desiccation cracks and fossil fragments. In spite of depositional gap described between the local Aratu and Alagoas Stages, the presence of Salvador Formation close to the north border fault may represent a rare rift phase record in the interior basins. The post-rift sequence is represented by the Marizal Formation, deposited during the Aptian. This formation is distinguished by the intercalation of fine sandstone, siltstone and conglomerate deposited in an alluvial fan environment. The pre-rift, rift and post-rift sedimentation are embedded in the depocenter of the basin, where the main NE-SWgraben stands out. A gravity survey was carried out, which obtained a negative, asymmetric Bouguer anomaly, with gradients added to the northwest, suggesting the existence of a half-graben. The result of the gravity 3D model indicates the existence of a main depocenter in the NE-SW direction with depths of up to 400 meters. These geophysical results support the tubular well location drilled 410 m in depth that was used in this work to better characterize the basin. The joint interpretation of gravity, aeromagnetic and structural data suggest that the half-graben framework of the basin developed by the evolution of a pull-apart extension system. The structural system that gave rise to the Mirandiba Basin has the maximum compression tensioner oriented to NE-SW and the distention to NW-SE. It has a depth of around 400 meters and the depressions formed by tectonic events were filled by Post-Tacaratu sedimentation.

An Exploration Model for A Gold Deposit in Kervian Area, Kurdistan Province, Iran, using a Combination of Geophysical Results with Geological Information and Other Exploratory Data

As many gold deposits are associated with sulfide zones, and the direct exploration of gold deposits using the geophysical methods is very difficult due to its low amount in the sub-surface, the direct exploration of sulfide zones by the geophysical electrical resistivity and induced polarization (IP) methods may lead to the indirect exploration of gold deposits. The gold deposit in the Kervian area is located in the Kurdistan shear zone, and is directly related to the sulfide, silica, and carbonate alteration units. After acquiring the resistivity and IP data, 2D modeling of the data is made in order to indirectly identify the gold-bearing zones in the surveyed area. As some of the identified geophysical anomalies indicating the sulfide zones may not be associated with the economic amounts of gold, in order to obtain an exploration pattern for the gold deposit in the studied area, a combination of the geophysical data modeling and interpretation results with the geological information and other exploratory data is used to reduce the uncertainty in identifying the gold-bearing zones in the studied area. Thus, modeling and interpretation of the geophysical data lead to identify the sub-surface anomalies as the locations of possible gold mineralization in the area, and then the drilling points are suggested in the area. Considering the geological studies and chemical analysis of the samples taken from the drilled boreholes crossing some of the geophysical anomalies, we conclude that the geophysical anomalies occurring inside the phyllite and carbonate units in the area can contain an economic amount of gold, and thus are recommended as the top priority for further exploration.

Integration of hydrogeophysical and geological investigations in enhancing groundwater potential assessment in Houtriver gneiss crystalline basement formation of South Africa

Groundwater exploration in crystalline basement aquifers such as the Houtriver gneiss formation in the Limpopo province of South Africa is often described as complex. This is because groundwater availability in such aquifers is largely a consequence of the interaction of several processes related to recharge, underlying geological features and fracture connectivity of the aquifer rock matrix. In this study, an integration of geophysical and geological investigations is applied in inferring potential drill targets within the Houtriver gneiss crystalline basement aquifer system. Results from the magnetic and frequency domain electromagnetic surveys were combined with geological investigations to identify sites where vertical electrical resistivity sounding was applied to infer the thickness and layering of weathered and fractured zones, as well as to identify potential targets where test boreholes were drilled. Constructed geo-resistivity pseudo-sections suggested that groundwater occurrence within this formation is described by a heterogeneous multiple-layered and fractured aquifer system with the main groundwater bearing zones ranging from a depth of 30–72m in most cases. Ten potential drill sites were identified from which three test boreholes were drilled and used to validate the results through a lithostratigraphic conceptual model developed from the correlation of the geophysical results with drill logs. The integration of hydro-geophysical and geological methods thus provided a comprehensive approach for resource assessment in the Houtriver gneiss formation.

Geological and geophysical investigations of an engineering site characterization for construction purposes in Western Saudi Arabia

Characterizing subsurface site conditions and understanding main geological features are critical components of any safety assessment for any construction, particularly defining subsurface flow paths and weakness (i.e. fracture and fault) zones. Poor definition of flow paths and weakness zones may lead to serious hazards during construction. This study, integrating geophysical and geological investigations, is undertaken to enhance the understanding of both surface and subsurface complexities of an engineering site characterization located in western Saudi Arabia near Red Sea. Two geophysical investigations, Electrical Resistivity Tomography (ERT) and Transient Electromagnetic (TEM), were carried out to characterize the subsurface of the study area. A total of three ERT profiles and sixteen TEM sounding measurements was conducted in the study area. Geological investigation was mainly focused to understanding geological features and bedrock conditions of the two opposite river's abutments at the study site. Geophysical results show NNE-SSW and NNW-SSE fault zones which were confirmed by in-situ geological inspections and by satellite images. The results also reveal the presence of geothermal fluids validated by the observation of hot water flowing in the river along the measurements. This study demonstrates that the integrated geophysical and geological investigations provide means to infer geothermal fluids, locate fractures, and fault zones. This study enabled us to characterize and locate the geological structural framework as well as possible geothermal fluids existence in the study area.

Shallow geophysical and hydrological investigations to identify groundwater contamination in Wadi Bani Malik dam area Jeddah, Saudi Arabia

Abstract The integration of geophysical techniques with hydrological investigation is frequently used for solving different geological and environmental problems including groundwater quality and exploration and seismic vulnerability assessment. In this research, the shallow geophysical techniques comprising of electrical resistivity profiling, vertical electrical sounding, and ground magnetic were used to identify the contaminated areas lying in the upstream and downstream of Almisk Lake in Jeddah. The chemical analyses of water samples collected from the wells located in the downstream and upstream areas were used to support these results as an increase in the total dissolved solids (TDS) shows a decrease in the resistivity value. The results of geophysical techniques and hydrochemical analyses show that the TDS values are significantly higher in the upstream area of dam than those of the downstream, which suggests that the contaminating source is lying in the upstream of the reservoir. Moreover, the dam was not completely successful to block the contamination because of improper base. The hydrochemical analysis and geophysical results clearly indicate that the groundwater is not suitable for drinking and irrigation purposes.

Ice content and interannual water storage changes of an active rock glacier in the dry Andes of Argentina

Abstract. The quantification of volumetric ice and water content in active rock glaciers is necessary to estimate their role as water stores and contributors to runoff in dry mountain catchments. In the semi-arid to arid Andes of Argentina, active rock glaciers potentially constitute important water reservoirs due to their widespread distribution. Here however, water storage capacities and their interannual changes have so far escaped quantification in detailed field studies. Volumetric ice and water content was quantified using a petrophysical four-phase model (4PM) based on complementary electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) in different positions of the Dos Lenguas rock glacier in the upper Agua Negra basin, Argentina. We derived vertical and horizontal surface changes of the Dos Lenguas rock glacier, for the periods 2016–2017 and 2017–2018 using drone-derived digital elevation models (DEMs). Interannual water storage changes of −36 mm yr−1 and +27 mm yr−1 derived from volumetric surface changes for the periods 2016–2017 and 2017–2018, respectively, indicate that significant amounts of annual precipitation can be stored in and released from the active rock glacier. Geophysical results show heterogeneous ice and water content with ice-rich permafrost and supra-, intra- and sub-permafrost water pathways at the end of the thaw period. Active layer and ice-rich permafrost control traps and pathways of shallow groundwater and thus regulate interannual storage changes and water releases from the active rock glaciers in the dry mountain catchment. The ice content of 1.7–2.0 × 109 kg in the active Dos Lenguas rock glacier represents an important long-term ice reservoir, as do other ground ice deposits in the vicinity, if compared to surface ice that covers less than 3 % of the high mountain catchment.

Geophysical and Geochemical Assessment of Afuze Bentonitic Clay: Implication for Mud Drilling Additive in Drilling Industry

Bentonitic clay is an important material required during drilling operation in oil and water industry. This study seeks to assess the deposit of the Bentonitic clay characteristics using geophysical techniques and geochemical assessment of the bentonitic clay unit in Afuze. Vertical Electrical Sounding (VES) using Schlumberger electrode arrangement were carried out along six traverses to determine the subsurface lithological characteristics of the area. Representative samples of the bentonitic clay layers were collected for X-Ray fluorescence (XRF) analyses and free swelling index parameters. The geophysical results show an appreciable thickness of the bentonitic clay unit among other stratigraphic units and are well defined based on its resistivity characteristic. The geochemical results show that the clay is a Ca-rich bentonitic type with a relatively low swelling properties and distinct to the Wyoming bentonite type. The Afuze bentonitic clay will be suitable for industrial application as drilling additives if beneficiated to increase the Na content in the clay and enhance its rheological properties for effective use in drilling operations.

Estimating the groundwater storage for future irrigation schemes

AbstractPresented in this paper is a feasibility study of groundwater for agricultural use (irrigation) in Northern Ghana. The study was conducted using geo-electrical data, boreholes drill logs, results of water quality, and results of the pumping test. The geo-electrical results were to unearth the lithology of the study area; it was found to be underlain with varying geology of both Precambrian and Paleozoic sedimentary formation. These formations consist of phyllite, schist, granite, meta-sediments, and meta-volcanics making up the Precambrian and sandstone, shale, siltstone, mudstones, granitiods also, of the Paleozoic sedimentary. Areas of low resistivity were targeted for drilling per the geophysical results of the profile, values between 24 and 100 ohm.m were zones of probable groundwater occurrence in the study. The groundwater storage capacity and the extractable storage capacity were estimated to be approximately 710,000 km3 and 290,000 km3. The pumping test results acquired from 81 boreholes from the study were used to analyze the sustainability. However, groundwater depth was studied using the Static water level (SWL), areas of SWL around 22 m and 25 m are likely to have a shallow depth whereas areas of 17 m would have deeper groundwater depth.

Salt layer characteristics in the Ghor Al-Haditha area, Jordan: comprehensive combined reprocessing of geophysical data

The presence of buried salt layer in the Ghor Al-Haditha area is discussed concerning sinkhole hazard. Numerous geophysical methods such as seismic refraction (SRFR), reflection (SRFL), seismic tomography, multichannel analysis of surface waves (MASW) were developed earlier for the salt layer identification. Geophysical criteria of salt parameters (such as longitudinal Vp and shear Vs wave velocities) were established to identify salt layers. This paper presents new geophysical results proving the salt extension in the Dead Sea (DS) coastal area in its eastern shore potentially representing a sinkhole hazard. The reprocessing technique of MASW data using the synthetic modeling enabled us to detect salt layer characteristics such as depth to its top, the thickness of the layer, and its Vs velocity. It was established that a salt layer with 7–10 m thick is located at a depth of 37–41 m and is characterized by shear-wave velocity (Vs) of 850–1200 m/s. Similar results were obtained by the Transient Electromagnetic (TEM) resistivity method, which detected a comparatively resistive salt layer at a background of very low resistivity. The resolution of the TEM method allows detecting a salt layer of 3 m thick and more at a depth of 39–40 m. Seismic refraction data processing has shown the presence of a salt layer with a velocity of more than 2900 m/s at approximately or the same depths. Analysis of seismic tomography data also confirms the parameters of the discovered target. Analysis of results of geophysical studies in the western and eastern DS shores, comparison of geological conditions in shores, and sinkhole development, enabled us to conclude with a high probability that salt layers exist in both shores and sinkhole development is determined here by similar mechanisms.

Multiple geophysical investigations to characterize massive slope failure deposits: application to the Balta rockslide, Carpathians

SUMMARYOrigins of ancient rockslides in seismic regions can be controversial and must not necessarily be seismic. Certain slope morphologies hint at a possible coseismic development, though further analyses are required to better comprehend their failure history, such as modelling the slope in its pre-failure state and failure development in static and dynamic conditions. To this effect, a geophysical characterization of the landslide body is crucial to estimate the possible failure history of the slope. The Balta rockslide analysed in this paper is located in the seismic region of Vrancea-Buzau, Romanian Carpathian Mountains and presents a deep detachment scarp as well as a massive body of landslide deposits. We applied several geophysical techniques on the landslide body, as well as on the mountain crest above the detachment scarp, in order to characterize the fractured rock material as well as the dimension of failure. Electrical resistivity measurements revealed a possible trend of increasing fragmentation of rockslide material towards the valley bottom, accompanied by increasing soil moisture. Several seismic refraction surveys were performed on the deposits and analysed in form of P-wave refraction tomographies as well as surface waves, allowing to quantify elastic parameters of rock. In addition, a seismic array was installed close to the detachment scarp to analyse the surface wave dispersion properties from seismic ambient noise; the latter was analysed together with a colocated active surface wave analysis survey. Single-station ambient noise measurements completed all over the slope and deposits were used to further reveal impedance contrasts of the fragmented material over in situ rock, representing an important parameter to estimate the depth of the shearing horizon at several locations of the study area. The combined methods allowed the detection of a profound contrast of 70–90 m, supposedly associated with the maximum landslide material thickness. The entirety of geophysical results was used as basis to build up a geomodel of the rockslide, allowing to estimate the geometry and volume of the failed mass, that is, approximately 28.5–33.5 million m3.

2-D Cross-Plot Model Analysis Using Integrated Geophysical Methods for Landslides Assessment

The large or small scale of a landslide is a natural, widespread process, resulting from the downward and outward movement of slope-forming materials, such as sculpting the landscape. Characterized landslide material and properties’ inhomogeneities conditions become a challenge as the process required the availability of a wide range of data, observations, and measurements with an evaluation of geological and hydrological conditions. Detailed investigations represent an essential component of the landslide risk mitigation process, relying on subsurface investigations, discrete subsurface sampling, and laboratory tests. To extend this approach, seismic refraction and two-dimensional (2-D) resistivity were utilized to study the landslides activities in Ulu Yam. The cross-plot analysis was introduced to integrate the geophysical results based on the criteria of the model. Velocity distributions from seismic refraction revealed the stiffness of the soil, where weak zones identified with values of Vp ≤ 1200 m/s, defined as threshold frequency for failure to occur. The 2-D resistivity shows that the weak zones were identified with resistivity values of <1200 Ωm. The 2-D cross-plot model gives a comprehensive interpretation where a low velocity and resistivity value represents the failure plane of materials to failure. The volume of mass sliding was calculated based on retrieved information from the model.

Subsurface structures and conceptual hydrothermal model of the area lying between Quseir and Safaga area, Red Sea Coast, Egypt

The study area is located in the Quseir–Safaga area of the Egyptian Red Sea Coast. This location considered one of the most promising areas for touristic villages depending on groundwater domestic uses as well as geothermal energy. The geothermal energy is considered one of the promising sources in the studied area. Nevertheless, few attempts have been carried out to evaluate the geothermal setting of the area. The present study aims to throw more light on studying the predominant structures in the area and their relation with geothermal manifestations, as well as defining the hydrothermal system type at the study area. Achieving this goal is dependent on using aeromagnetic data in the form of reduced to northern Pole (RTP) anomalies. These data were subjected to different techniques of processing and interpretation through both qualitative and quantitative analyses. Two-dimensional (2D) modeling of aeromagnetic data has been used to simulate the subsurface structure configuration along some selected profiles trending in NW-SE and E-W directions. In addition, a conceptual model of the hydrothermal system was built based on geophysical results of the aeromagnetic data analysis and processed numerically to obtain a 2D hydrothermal model that contains all simplifications and assumptions made on the conceptual model. The HYDROTHERM Interactive (HTI) program version 3 was used for two-dimensional simulation in the study area to study the temperature and pressure distributions beneath the study area. The results of the study showed that the depth to basement from the ground surface ranges from 20 to 1200 m. The hydrothermal simulation in the area indicated that the origin of thermal water is due to high heat flow and deep groundwater circulation controlled by structures in the subsurface reservoir. Under the thermal water, the water speeds up and flows through the fractures and faults. In general, the high heat flow in the Eastern Desert is associated with shallow basement depths. Thus, the modeled hydrothermal system is considered a dynamic type.

Geophysical assessment of Verteba Cave Eneolithic site, Ukraine

AbstractThe set of geophysical methods employed above ground and inside Verteba Cave Eneolithic Trypillian Culture Site (Ukraine) includes magnetic survey, electrical resistivity tomography (ERT), and ground‐penetrating radar (GPR). The above‐ground geophysical study was aimed at the recognition of lateral and vertical distribution of sulfate karst landforms and archaeological targets. In‐cave measurements were made to prospect archaeological remains in loose infill and unknown voids. The round and oval‐shaped magnetic anomalies with dimensions of 10–25 m and maximum intensity of 15–20 nT are caused by old refilled collapse dolines that were discovered over the cave. The magnetic survey proved the absence of Trypillian culture houses on the surface and the presence of buried archaeological objects in the cave. 2D ERT imaging revealed the vertical structure of karstic collapse dolines, the thickness of the sedimentary layer over gypsum, as well as loamy cave infill. ERT was capable of detecting the void in gypsum by resistivity enhancement up to several thousand ohm‐meters. The underground GPR survey of cave walls provided information about possible vertical air−gypsum and loam−gypsum interfaces within the gypsum layer. The prospective areas for future archaeological excavations and the possible location of undiscovered cavities were outlined on the basis of geophysical results.

Detection, imaging and analysis of lava tubes for planetary analogue studies using electric methods (ERT)

This paper presents new field and synthetic modelling results of Electrical Resistivity Tomography (ERT) surveys for the identification and detection of lava tubes with the particular aim of using ERT techniques for stratigraphic investigations of planetary volcanic analogues. These geophysical surveys were undertaken at the Corona volcano (Lanzarote, Canary Islands), as part of the PANGAEA-X 2017 campaign, which formed part of the European Space Agency's (ESA) astronaut training program. ERT profiles were acquired at two test sites located along the main Corona lava tube system. During the campaign a variety of experimental setups were tested. This provided an ideal opportunity to cross-validate geophysical results with ground truth provided by partial surface exposure of the lava tubes and laser scanner mapping of the lava tube system in the subsurface. It also permitted an assessment of the usability of ERT in detecting lava tubes in a heterogeneous volcanic setting. Our experiments showed that a combination of different electrode arrays and their joint inversion resulted in good detectability of the lava tubes with a large size with respect to the electrode spacing. The dipole-dipole array configuration provided more accurate models for lava tubes of a size in the same order of magnitude as the electrode spacing. This study showed that the main drawbacks of ERT in heterogeneous volcanic settings are linked to lava tube-related high-resistivity anomalies which appear larger and shallower and may also be laterally shifted with respect to their true location. For lava tubes with a small size with respect to the electrode spacing our synthetic data modelling results show the difficulty in distinguishing single lava tubes from in contact lava tubes, and distinguishing lava tubes in general from void-rich zones. Overall, ERT surveys were successful in detecting lava tubes, providing a good definition of the main boundaries between different volcanic units and highlighting the presence of close, near-parallel unexplored lava tubes.

Lithospheric mantle underneath the Tibetan Plateau does not escape southeastward

A mass of lithospheric shortening occurred beneath the Tibetan Plateau due to the collision between the Indian and Eurasian plates. The extrusion of the upper crust beneath the Tibetan Plateau has been widely accepted, but whether the lithospheric mantle escapes laterally by creep deformation or rigid-block extrusion remains unclear. Based on the Pn travel time data, the velocity structure of the uppermost mantle in eastern and southeastern Tibetan Plateau was obtained by using the interstation travel-time difference method. The results show an obviously high Pn velocity beneath the Sichuan Basin and Qaidam Basin, indicating that the areas are stable blocks. The high Pn velocity beneath the eastern Lhasa terrane may be related to the underplating of the Indian lithospheric plate to the north. The Qilian block located in the north of the Kunlun fault appears as a normal Pn velocity, which indicates a mean lithospheric mantle thickness. A significantly low Pn velocity with an average of ~7.8 km/s in eastern and southeastern Tibetan Plateau, including the eastern Songpan–Ganzi terrane, the Chuan–Dian Diamond Block, and the northern part of Yunnan Province, indicates that the lithospheric mantle is relatively thin in these regions. Combined with other geologic and geophysical results, we propose that the lithospheric mantle of the plateau did not escape to eastern and southeastern Tibetan Plateau where the crust has been thickened by adding crustal material from the interior of the plateau.

Evolution of a crustal-scale silicic to intermediate tectono-magmatic system: The ~2600–2300 Ma Bundelkhand granitoid, India

Understanding the petrogenesis of crustal-scale silicic magmatic systems is a major research frontier. The ~2600–2300 Ma granitoid covering >90% of the exposed part of the >26,000 km2 Bundelkhand Craton in northcentral India is considered so far to have resulted from melting of Tonalite-Trondhjemite-Granitoid (TTG) gneiss at the mid-upper crustal level aided by radioactive heat generated from the U-enriched upper crustal rocks within a period of 60–80 Myr. Here we combine new field, petrographic/microstructural evidences, mineralogical and geochemical data, along with published geochemical/mineralogical, geochronological and geophysical results to develop a unified model that highlights the deeper crustal melting and crustal reworking mediated by repetitive mantle-derived mafic recharge over ≥300 Myr in a common specific stress regime that has controlled the evolution of Bundelkhand granitoid. Our main findings include: (a) Ti-in quartz, apatite and zircon saturation, and primary biotite thermometry indicating high liquidus (≥900 °C) for the granitoid magma that crystallized over ~200 °C (~≥900°–706 °C); (b) magmatic epidote, amphibole (Fe-rich hastingsite to magnesiohornblende), and magmatic titanite indicate a polybaric crystallization of the ascending magma from the deeper crust (~9 kb) through the middle (5–6 kb) to shallow crust (1–2 kb); (c) polybaric crystallization (≤5–10 kb) for mafic magma manifested in magmatic enclaves and mafic dyke swarms; (d) large-scale silicic-mafic magma interactions and (e) crystallization and emplacement of both silicic and mafic magma under a common stress regime. Unlike closed-system dehydration melting, the influx of mantle-derived supercritical basaltic magma provided not only heat and material but also supplied fluids in the deeper crust in a sustained tectono-magmatic condition. We conclude that the intermittent H2O-rich mafic recharge is key to large granitoid production in a dynamic crustal-scale magmatic system worldwide irrespective of tectonic setting.

Use of the geophysical approaches for studying the environmental impact assessment of the human burying techniques to the soil and groundwater: A case study of Geheina cemeteries, Sohag, Egypt

Electrical resistivity and self-potential are effective geophysical tools for monitoring the soil and groundwater pollution because they are accurate, rapid, costless and non-distractive techniques. Direct or indirect burying of the corpses into the soil is one of the main factors which pollute the soil and the groundwater after decomposition of the tissues and bones. Therefore, the main objective of this study are using these tools to evaluate the rate of soil and groundwater pollution due to burying the corpses in chipboard coffins at depths approximately 0.70–1.30 m (Christians burial method) and directly into the soil at depths about 1.5–1.8 m (Muslims burial method). Beside, assessing the contamination depths and flow paths of the groundwater investigated area. The study area was carefully chosen because of: 1- it contains two different burial methods, 2- presence of shallow groundwater aquifer, 3- the surface layer which contains the burial depth is porous and permeable, 4- the cemeteries are near enough to the population density and agricultural lands. The study area was divided to three main sites; site 1, site 2 and site 3 for Christian cemeteries, Muslims ones and control area that does not contains any cemeteries respectively. Five two-dimensional electrical resistivity tomography (ERT) profiles were surveyed and analyzed using RES2DINV software (two profiles on the site 1, two profiles on the site 2 and one profile on the site 3). 121 points of vertical electrical sounding (VES) at the same depth were collected and analyzed in 3D iso-resistivity map. Self-potential survey (SP) were performed on the same 121 points of VES stations for comparison where the data was contoured to build 3D iso-potential map. The geophysical results were correlated with the available borehole data. The results revealed presence of three resistivity zones of high resistivities (1000–3000 Ω m), moderate ones (50–1000 Ω m) and low ones (<50 Ω m). The main constituents of these three zones are clastic sedimentary rocks with different grain sizes. The rapid decreasing in the resistivity values in the site 2 than that in the site 1 is resulting from the rapid decomposition of the death bodies due to direct burying in the ground without coffins leading to more pollution rates of the soil and the groundwater than burying in coffins. Increasing of the burial depth causes increasing of the contamination rate of the shallow groundwater aquifer. Positive and negative values of potentials were recorded in 3D iso-potential contour map reflecting the flow direction from low to high potentials. The negative values were attributed to the leakage of more the putrefactive liquid resulting from decomposition of the death body. Positive potential values were caused due to the semi-fluid masses consisting of water and putrefied tissues which are mostly generated by the corpses buried in coffins with less amount of fluids and the putrefactive liquid evaporation and low humidity.

A multidisciplinary approach for landslide residual risk assessment: the Pomarico landslide (Basilicata Region, Southern Italy) case study

On 25 and 29 January 2019, a large landslide destroyed an important part of the town of Pomarico (Basilicata Region, Southern Italy). Geological and geomorphological investigations provided a detailed description of the landslide features. Several geophysical surveys were carried out to deepen knowledge of the landslide and the residual risk assessment. Detailed electrical resistivity tomography (ERT), multichannel analysis of surface waves (MASW), and seismic refraction tomography (SRT) have been used to analyze geomorphological evidences of the failure and the potential kinematic evolution of the landslide scarp, a crucial factor to assess landslide residual risk. The joint analyses of the geophysical results, compared with geological and geomorphological data, allowed to obtain detailed information about the stratigraphic contact between clayey and sandy deposits in the crown area of the landslide, and to identify the post-failure stability condition changes in sands. The geophysical analyses confirmed the presence of multiple old degraded scarps developed over time and provided information on the decompression state of the different areas of the landslide crown. The results highlighted a subparallel stratification consisting of an anthropic surface carry-over material, which covers a layer of sands with silty intercalations, overlying clayey material that represents the bedrock of the investigated area. Furthermore, natural and anthropogenic caves, mainly developed in well-cemented layers of sands, were identified. This study emphasized how the integration of different geophysical methods constitutes a capable tool for characterizing landslides, contributing to assessing the landslide residual risk of the slope mass and evaluating the suitability of the methods in relation to the investigated landslide conditions.