Basaltic Sheet Research Articles

Detection of subsurface basaltic sheets and associated structures utilising forward modelling and inversion of 2D electrical resistivity data: A case study from Jebel-Qatrani, Fayoum, Egypt

In the north of Fayoum Governate, Egypt, numerous extrusive flows of basalt rocks exposed on the surface and affected by weathering and erosion, forming altered basalt sheets which is the case of the Jebel-Qatrani. The study objective comes in two main folds: the first, to choose the optimum parameters required for the filed survey by generating forward models using several arrays with 3% Gaussian random noise, simulating the geology of the study area deploying a finite element modelling approach; the second, to acquire the real field data and generate the electrical resistivity tomograms to ascertain the existence, extension, and characteristics of the basaltic sheets in the subsurface. Hence, four electrical resistivity profiles with a Wenner-alpha array with 48 electrodes, 5 metre electrode spacing, and a total length of 235 metres were acquired in suitable locations based on previous aeromagnetic results in the vicinity of the study area. These profiles were inverted to derive the true resistivity distribution of the subsurface. Another objective is to detect the near-surface, Oligocene normal faulting structures associated with rifting of the Red Sea. Results from two inverted resistivity tomograms show a possible normal fault cutting through the early Oligocene Qatrani Formation at the same time as red sea rifting, confirming previous geological studies in the Fayoum region based on satellite imagery, aeromagnetic data, and geological outcrops. It is concluded that near these faults, a sheet-like body of relatively high resistivity values, representing basaltic extrusions, was detected, confirming that the basaltic presence is associated with these structural zones.

Новые 40Ar/39Ar-данные долеритов Канино-Тиманской провинции внутриплитного магматизма (п-ов Канин)

The Kanin-Timan region is located in the north-east of the European part of Russia and represents the western edge of the Timan-Pechora Plate. In the Devonian time, the Kanin-Timan region experienced rifting processes caused by the influence of a mantle plume. As a result of these processes, the Kanin-Timan dolerite complex was formed, which includes dolerite dikes and basalt sheets. The rocks of the complex have been studied throughout the study region. In the Middle Timan, the basalt plagioclase of the Upper Vorykva cover was dated by the 40Ar/39Ar method, the dating result indicates an age of 389 ± 6 Ma. Dolerites of the Kanin-Timan complex were also dated by the K-Ar method in the last century. As a result of dating, conflicting data on the absolute age from 378 to 288 Ma were obtained. To clarify the age of dolerites, 40Ar/39Ar dating was carried out. According to the isotope age data, the dolerites of the Kanin Peninsula are 419 ± 8 Ma, the age of the basalts of the Upper Vorykva cover is 389 ± 6 Ma. Thus, the magmatic activity that led to the formation of the Kanin-Timan complex in the Kanin-Timan region began earlier on the Kanin Peninsula, and then on the Timan. According to the research results, we believe that the Kanin-Timan complex began its formation in the Early Devonian with the peak during the Middle and Late Devonian time.

Ground Magnetic Surveying and Susceptibility Mapping Across Weathered Basalt Dikes Reveal Soil Creep and Pedoturbation

Ground magnetic survey profiles across a soil-covered and weathered mafic dike in sedimentary host rock not only permit to delineate the strike, width and burial depth of the intrusive basalt sheet, but also reflect the subsurface deformation of its clayey weathering products. We illustrate this finding and its practical geomorphological applicability by an example from the mid-German Heldburg Dike Swarm, where blue- and olive-gray basalt-derived clays inherited not just the dike space previously occupied by the basalt, but also large parts of its magnetic iron minerals and their strong induced and remanent magnetization. Such ductile basaltic “marker soils” deform and move with the surrounding low-magnetic host soils, but remain distinguishable by their contrasting colors and high magnetic susceptibility. Ground magnetic surveys can therefore delineate soil creep distance at meter- and basalt weathering depth at decimeter-precision. Magnetic mapping of a weathered dike’s cross-section from an exploration trench by in-situ susceptometry permits to analyze past soil deformation in great detail. Weathering and solifluction transforms the simple “vertical sheet” anomalies of dikes into complex, but still interpretable composite patterns, providing a new and promising exploratory approach for field studies concerned with soil creep and pedoturbation.

Prediction of Flexural Moment of Reinforced Concrete Beam in Reinforced Basalt Sheets

Prediction of Flexural Moment of Reinforced Concrete Beam in Reinforced Basalt Sheets

Characteristics of lava-sediments interactions during emplacement of mid-Tertiary volcanism, Northeastern Desert, Egypt: field geology and geochemistry approach

Mid-Tertiary volcanism in the Northeastern Desert of Egypt was associated with the African-Arabian plate rifting and opening of the Red Sea, a period of 30 Ma (Late Oligocene). The resulted lava flows, predominately basaltic sheets, have mingled with the underlying sediments, forming peperite along the contact between them. Field geology, petrography, and geochemistry methods have been used to identify the behavior of the lava-sediment interaction which produced peperite. Two types of peperite have been recognized, fluidal at Naqb Ghul and El-Yahmum areas, and blocky at El-Qattamiya area. Sometimes, the two types are represented together at the El-Qattamiya area. Fluidal peperite is characterized by globular and equant juvenile clasts and with irregular or ragged margins suggesting low viscosity, ductile fragmentation, and sediment fluidization. Blocky peperites are characterized by angular, polyhedral, platy juvenile clasts and a jigsaw-crack texture, resulted from quenching of magma in a brittle regime. The coexistence of fluidal and blocky clasts together reflects progressive disintegration and suggests decreasing temperature and increasing viscosity during fragmentation. The presence of sediments in vesicles and in fractures in the peperite zone indicates a non-explosive phase of interaction. Geochemical data suggests that different composition across the magma/sediment boundary is a result of silicification and sediment fluidization.

Landforms Evolution of Wadi Qudaid Area, West Central Arabian Shield, Saudi Arabia: An Example of the Role of the Geological Factors in the Urban Extensions

Wadi Qudaid is located in the west central part of Saudi Arabia. It about 135 km to the northeast of Jeddah city along Al Haramein highway and it represents the upstream of the very large alluvial plain along the Red Sea coast. It runs in NE direction parallel to many wadis of the west central part of Saudi Arabia i.e. Wadi Fatima, wadi Sitarah. The wadi floor is filled by Quaternary deposits which represent good groundwater aquifer. Geologically, the present-day residual landforms of Wadi Qudaid are composed mainly of Precambrian Arabia shield rocks overlained by Tertiary sedimentary rocks and finally harrat (Tertiary volcanic). The Precambrian rocks are represented by 1) a lower layered basic and intermediate volcanic and the intercalated volcaniclastics. This unit is correlatable with Samran Group, 2) an upper layered acidic volcanic and the intercalated acidic volcaniclastics. The Arabian shield rocks are intensively folded and dragged along the major NE faults. They are directly overlain by Tertiary basic volcanic (harrat) and the related volcanoclastic red beds). The main geomorphologic elements of the study area include plateau, scarps, and the wadi floor. The plateau is represented by the black basaltic sheet that contains some semi-rounded depressions filled with Quaternary eolian sands. The scarps of the main wadi and its tributaries are nearly steep and contain many asphaltic roads with some isolated cone hills detached from the scarps. Geomorphological, Wadi Qudaid represents the incomplete erosion cycle that begins with the formation of deep galleries and very steep and narrow wadies formed along the major NE faults and related fractures and folds. The progress of the erosion processes led to the formation of narrow interfluves as a result of pedimentation and sculpturing of the wadies sides by scarp retreat. The peniplanation stages of the erosion cycles are reached in the southwestern and the central part of the wadi where fast peniplained areas were formed. The results of this study revealed the role of the different geological processes (lithology, structural elements and climatic conditions) in the distribution of present-day human populations in urban extensions. Qudaid, Dhubaya-Jumah, Dabyah, Al Khamrah, Almansa and Al Massamah are the main villages of Wadi Qudaid area.

Cretaceous magmatic evolution in the Deylaman igneous complex, Alborz zone, Iran: change from extensional to compressional regime

The Deylaman igneous complex, as a part of the Late Cretaceous rock unit that lies behind the Paleogene Alborz magmatic arc, in the northern Alborz zone, is composed of basaltic sheet lavas alternating with the pelagic calcareous sediments, basaltic pillow lavas, felsic lavas and gabbroic-monzodioritic intrusions. The pelagic calcareous deposits contain microfossils representing the Santonian–Maastrichtian ages. Furthermore, petrographic textures such as the hyalomicrolitic texture and swallow-tail plagioclase crystals in the pillow lavas, and also segregation vesicles in the basaltic sheet lavas, imply high external (hydrostatic) pressures as the magma was extruded in a deep-water environment. The rock samples show both compositional bimodality and characteristic trends in the variation diagrams. Also, some geochemical characteristics imply that the basaltic lavas originated from the partial melting of an undepleted deep mantle source containing spinel lherzolite: the enrichment patterns of LREE/HREE ratios of the samples [(La/Yb)n = 3.93–4.16 for basaltic lavas and 10.92 for felsic lavas] lying between those characteristic of OIBs [(La/Yb)n = 12.92] and EMORBs [(La/Yb)n = 1.91]; similarities between the patterns of multi-element spider-diagrams; LILE bulges in the basaltic samples compared with those of OIBs. Moreover, the samples show influence from two geotectonic environments: supra-subduction zone (SSZ) settings and plume-type within-plate magmas. Therefore, because of the deep submarine environment inferred for the effusive volcanic eruptions in Santonian–Maastrichtian time, it seems that the Deylaman igneous complex evolved through two stages: first, a tensional regime in a supra-subduction zone (farther from the Mesozoic magmatic arc) and formation of an embryonic rift-related oceanic basin in the Late Jurassic–Early Cretaceous; secondly, a compressive regime in the Late Cretaceous–Early Paleocene and inland migration of the magmatic arc. Consequently, the Cretaceous magmatism can be interpreted as a prelude to the Eocene magmatic flare-up in the magmatic arcs of Iran.

Shallow marine basaltic volcanism of the Machadodorp Member (Silverton Formation, Pretoria Group), Transvaal Basin, South Africa — An example of Paleoproterozoic explosive intraplate volcanic activity in an epeiric embayment

The early Paleoproterozoic Machadodorp Member of the Silverton Formation (Pretoria Group, Transvaal Supergroup), South Africa, is an example of ancient submarine explosive volcanism in an intra-cratonic setting under incipient rifting conditions. The Silverton Formation consists of three different members, which include, in ascending order, the Boven Member, the Machadodorp Member and the Lydenburg Member. The formation is primarily characterized by the muddy sediments of the Boven and Lydenburg members, which formed in a relatively shallow submarine environment, predominantly as sub-storm wave-base pelagic deposits, within an epeiric embayment on the Kaapvaal Craton. The subaqueous Machadodorp Member volcanic activity is mostly distributed in the eastern part of the basin. So far, the volcanism of the Machadodorp Member has not been studied in detail. Therefore, a detailed facies analysis of its volcanism was initiated, allowing constraints on its volcanic evolution.The Machadodorp Member consists of a basal unit of basaltic sheet lava, followed by a fining-upward succession of volcaniclastic rocks, ranging from breccias, tuff-breccias and tuffs, rich in fluidal-shaped clasts, to laminated tuffs that are related to subaqueous mass flows, and a final sheet lava that characterized the end of volcanic activity in the section studied.The Machadodorp Member rocks are tholeiitic basalts in composition, with all samples plotting in the low-TiO2 suite. Fractional crystallization of clinopyroxene, olivine and plagioclase was the predominant evolutionary process as illustrated by mineral chemistry and major element geochemical modeling. AFC (Assimilation and Fractional Crystallization) processes could not account for all the trace element variations, nor for the arc-like signatures observed on the primitive mantle normalized plots. Variable ancient mantle enrichment beneath this area is a more plausible cause for the trace elements variations observed in the Machadodorp rocks. Trace element modeling indicates that the parental composition of these rocks was a variably enriched spinel lherzolite source. Such enrichment must have occurred before 3 Ga during episodes of arc collision and subduction.

Ground follow-up of the airborne gamma-ray spectrometric survey data, ramlet HOMAYYER area, east abu-zeneima, southwestern Sinai, Egypt

Ramlet Homayyer area is located in the southwestern part of Sinai Peninsula, Egypt, to the east of Abu-Zeneima city, located on the eastern coast of Gulf of Suez, Red Sea. The Paleozoic succession in the study area (up to 300 m thick) overlies the basement complex and is covered by basaltic sheets. The lithologic nature of the Paleozoic rocks played a very important role in the localization of various mineralizations (e.g. Mn, Fe, Cu, REEs, Th … etc.)In the present study of Ramlet Homayyer area, ground spectral gamma-ray survey was conducted along N-S profiles, equally-spaced, with lengths of about 2.5 km, and the total area equals about 10 km2. The measurements were conducted using a portable gamma-ray spectrometer, model GS-512. The examination of the total-count (T.C.) radiometric contour map shows that the radioactivity values vary widely from 3.4 Ur to 101.3 Ur. The potassium (K) content in Ramlet Homayyer area ranges from 1.2% to 16.0%. The equivalent thorium (eTh) content in the study area has a maximum value reaching about 68.9 ppm. The equivalent uranium (eU) content attains its maximum value reaching about 84.0 ppm. Factor analysis technique, which provides a way of thinking about radiospectrometric elements and ratio interrelationships alltogether was carried out.The application of factor analysis technique, helped to delineate the zones of high concentrations of eU, eTh and K separately, where the first factor (F1) can delineate high eU zones, (F2) high eTh zones and (F3) high K zones. The radiometric lithologic mapping was conducted for the whole area, by testing the homogeneity of all measurements recorded indicates that the distribution of the radioactivity all over the area is not homogeneous. This indicates that the lithological cover of the study area cannot be considered as one lithologic unit, but contains different types of rock units. Each Interpreted radiometric lithologic units (IRLU) is corresponding to one geomorphological mass or features.As a result of the ground radiometric survey of the study area, chemical analyses for some selected samples were taken and conducted from the anomalous zones at G. Homayyer, G. Ghorabi and Khameila areas. These analyses showed presence of concentrations of uranium up to 147 ppm, 58 ppm, 52 ppm in addition to trace elements with high concentrations of some elements as: Y, Cr, W, Sr and Ag, which gives 6819,768,314,561 and15 ppm respectively.

Magnetostratigraphic dating of the late Miocene Baogeda Ula Formation and associated fauna in central Inner Mongolia, northern China

Detailed understanding to the evolution of Neogene land mammals in East Asia and its intercontinental correlation has been impeded by the absence of an integrated biochronological system of this region. The numerous and diverse records of Neogene vertebrate fossils preserved in Inner Mongolia of northern China play a key role in the establishment of an independent biochronological framework in East Asia. However, most of these faunas are poorly constrained by independent chronological controls due to the scattered distribution of fossil localities and insufficient exposure of the fossiliferous strata. Additionally, age estimates by mammalian evolution and correlation often have uncertainties greater than ~1–2 million years. Here we present new magnetostratigraphic results of the Baogeda Ula Fauna, which was generally assigned an early Baodean Age (Late Miocene), or equivalent to the European MN12 zone (middle Turolian). Hipparion remains and associated vertebrate fossils were excavated from the upper part of the fluvio-lacustrine Baogeda Ula Formation near Abaga Banner, central Inner Mongolia of northern China. At least two layers of basalt sheet flows can be observed on top of the Baogeda Ula Formation. Our magnetostratigraphy, aided by published biochronology data and K–Ar ages of the lower basalt layer suggests that the Baogeda Ula Fauna consisting of three fossiliferous horizons can be placed within chron C4n.1n with an age range of 7.642–7.528 Ma. Thus, the Baogeda Ula Fauna becomes the first and only Baodean assemblage that is constrained by both magnetostratigraphy and radiometric ages, offering an anchoring point for future biochronological correlations.

Sub-surface geology and velocity structure of the Krafla high temperature geothermal field, Iceland: Integrated ditch cuttings, wireline and zero offset vertical seismic profile analysis

The Krafla geothermal area in northern Iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone. Of key importance to improved resource exploration and development in volcanic areas such as Krafla, is the interpretation and understanding of the subsurface geology. Within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the K-18 borehole within the Krafla caldera based on combined wireline, ditch cuttings, and zero-offset VSP (vertical seismic profile) analyses. This study presents the first published sonic log velocity data from a high temperature geothermal borehole in Iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations. The shallow subsurface geology of the K-18 site from c. 0–380m comprises an inter-layered sequence of sub-aerial basaltic lavas, hyaloclastites and tuffaceous lithologies of both felsic and basic composition, which are progressively replaced by basaltic sheet intrusions with increasing depth. An interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis, gamma and sonic velocities between c. 790–1120m depth. Discrete high sonic Vp units cut the lower c. 100m of this interval and are interpreted as either sheet intrusions or lava interiors. At c. 1800m, a sharp increase in P-wave velocity from c. 4.5 to c. 5.5km/s, represents the transition from a mixed lava and sheet intrusion dominated sequence, into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c. 2215m. Reduced travel time analysis of processed zero-offset VSP results reveal good correspondence with the major stratigraphic boundaries in the borehole, supporting the potential for VSP studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields. Finally, the application of percentage-based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential.

Petrographic Characterization of the Different Types of Basalts of Harrat Al Fatih, Ablah Area, West Central Arabian Shield, Saudi Arabia

Harrat Al Fatih is located southwest of Ablah area, Assir terrain, southwestern Arabian Shield. It is present as black laterally extended horizontal basaltic sheet just overlying folded strata of the volcano-sedimentary succession of Ablah Formation (green mudstones, dolostones and green and red volcaniclastic red beds). These basalts are rift-related and represent part of the Oligo-Miocene basic volcanics of the western part of Saudi Arabia. The detailed field and microscopic description of these basalts enable the author to classify it into two main types: 1) Grey tuffaceous glassy basalts that present overlying the Ablah Formation. This basalt type is generally soft, bedded and intercalated with grey, green and red tuffaceous mudstones. Microscopically it composed of minute lath-like plagioclase and pyroxene crystals embedded in glassy groundmass. 2) Black olivine-rich basalts which are present in the topmost part of harrat Al Fatih are generally black, hard and contain remarkable reddish brown oxidized olivine spots and some calcite and amorphous quartz domains. Under the microscope, this basalt type is microcrystalline and composed mainly of lamellar twined Ca-plagioclase and colored olivines and pyroxenes. The olivines show different stages of oxidation and formation of amorphous blood red iron-oxyhydroxides and black hematite. The present study revealed the formation of the grey basalts at the initial stages of the volcanic eruption in ephemeral lakes and the second type of basalt was during the consolidation of proper basic magmas at the final stages of the volcanic eruption.

Application of electrical resistivity method for groundwater exploration at the Moghra area, Western Desert, Egypt

Moghra territory is one of the most encouraging regions for watered farming and development in the northern part of Western Desert. To achieve that development groundwater is considered the most favorable tool. Geophysical survey in terms of geoelectrical resistivity sounding has been conducted using the Schlumberger array – eleven vertical electrical soundings (VES’s) were measured on the study area. The aim of this study was to investigate the hydrogeological condition at the area under investigation.Three geoelectric sections are prepared; each of them is composed of four units. The first layer has resistivity ranging from 58 to 2029ohm.m and thicknesses from 0.46 to 10.7m characterizing a gravely sand facies of Quaternary age (Pleistocene to Holocene). The second geoelectrical layer has resistivity values ranging between 188 and 518ohm.m which are comparatively high, with various depths varying between 14.7 and 25.8m from Lower Miocene age. It is formed of sand and gravel. The third geoelectrical layer is considered the aquifer for the area under investigation with moderate electrical resistivity values (17–111ohm.m), and could be recognized sometimes as the most extreme depth of penetration. At the maximum depth of penetration of this area, the lower layer (fourth layer) was recognized with the highest electrical resistivity values (1227–8935ohm.m) of basaltic sheet (Precambrian age).Structurally, the study area is influenced by three faults two of them are geological/geoelectrical faults forming a graben structure at the central part; the third fault is a geoelectrical fault and is located to the west of the graben structure forming a horest structure.

Delineating groundwater and subsurface structures by using 2D resistivity, gravity and 3D magnetic data interpretation around Cairo–Belbies Desert road, Egypt

Geophysical tools such as magnetic, gravity and electric resistivity have been used to delineate subsurface structures, groundwater aquifer around Cairo–Belbies Desert road. A dipole–dipole section was measured at the central part of the study area with 2100m length and electrode spacing 50m for greater penetration depth. The results of the inverse resistivity data indicate that the study area includes two groundwater aquifers at different depths. The shallow aquifer water is near the surface and the deep aquifer lies at depth of about 115m and exhibits low resistivity values ranging from 20 to 100ohmm.One hundred and fifty-two gravity stations were measured using Autograv gravimeter (CG3), different gravity corrections (drift, elevation and latitude corrections) were applied. The corrected data represented by Bouguer anomaly map were filtered into regional and residual gravity anomaly maps. The residual gravity map indicates that the area is dissected by many faults with NW-SE, N-S, E-W and NE-SW trends.One hundred and fifty-three ground magnetic measurements are collected using two Proton magnetometers (Envimag). The corrected magnetic data are represented by total magnetic intensity map that was reduced to the magnetic pole. 3D magnetic modeling was applied to detect the depth of basaltic sheet and basement complex. The results indicated that the elevation of upper surface of basalt is ranging from 148 to −153m and the elevation of lower surface of basalt is ranging from 148 to 269m.

The volcanological and petrogenetic origins of the basaltic Flinders Volcanic Province (49–39 Ma), Older Volcanics Provinces, southeast Australia

Eocene age basalts within the Mornington Peninsula represent a segment of volcanics constituting the Flinders Volcanic Province, one of the Older Volcanics Provinces, in Victoria, Australia. Section logging at selected coastal sites between Cape Schanck and Flinders, within the Mornington Peninsula National Park, has depicted a succession of gently southeasterly dipping basaltic pahoehoe sheet lavas and localised debris flows, emplaced in a subaerial environment, and distinguished by post emplacement altered weathering horizons. Eight dykes intrude the volcanic succession, controlled structurally by NW normal and NE-trending transform faults of the Gippsland Basin, forming swarms at the West Point Gunnery Range in Flinders, Cairns Bay and Cape Schanck. Geochemical analysis of the lava succession suggest the influence of multiple magma batches, each enriched in light rare earth elements, which based upon Sr–Nd isotopic data came from a long-term incompatible element depleted magma source.

Geological sketch and the non-karstic caves of the Bakony Mountains in Hungary

The about 4000 km2 Bakony Mountains form the most extensive region of the Trans-Danubien Mountains between Lake Balaton and Marcal River. They have a typical medium relief, including plateaux of various heights, and denudated fault blocks interspersed with inter mountain basins. In the southern and western areas of the mountains, basalt cones and basaltic sheets are frequently found. In the central area, the variously sloping landscape is inclined towards the blocks. Limestone and dolomite predominate, and there are extensive karst regions and numerous karst caves. Of course, from the point of view of the non-karstic caves, these regions are insignificant. Significantly smaller is the occurrence of quartziferous (sandstone and conglomerate) and basalt rocks, however 147 non-karstic cave are known in these rocks and, in addition, 35 artificial cavities, considered as caves, are listed. The authors describe the geology, the geomorphology and the non-karstic cave development of the Bakony Mountains. Furthermore, typical examples of the caves have been selected and presented according to the different rock formations and development types.

Assessment of subsurface structural elements around greater Cairo by using integrated geophysical tools

Geophysical techniques such as gravity, magnetic and seismology are perfect tools for detecting subsurface structures of local, regional as well as of global scales. The study of the earthquake records can be used for differentiating the active and non-active fault elements. In the current study, more than 2,200 land magnetic stations have been measured using two proton magnetometers. The data are corrected for diurnal variations and then reduced by the International Geomagnetic Reference Field. The corrected data have been interpreted by different techniques after filtering the data to separate shallow sources (basaltic sheet) from the deep sources (basement complex). Both Euler deconvolution and 3-D magnetic modeling were carried out. The results of interpretation indicate that the depth to the upper surface of basaltic sheet ranges from <10 to 600 m, depth to the lower surface ranges from 60 to 750 m, while the thickness of the basaltic sheet varies from <10 to 450 m. Moreover, gravity measurements are conducted at 2,250 stations using a CG-3 gravimeter. The measured values are corrected to construct a Bouger anomaly map. The least squares technique is then applied for regional–residual separation. The third order of least squares is found to be the most suitable to separate the residual anomalies from the regional one. The resultant third-order residual gravity map is used to delineate the structural fault systems of different characteristic trends. The trends show an NW–SE trend parallel to that of Gulf of Suez, an NE–SW trend parallel to the Gulf of Aqaba and an E–W trend parallel to that of the Mediterranean Sea. Taking seismological records into consideration, it is found that most of the 24 earthquake events recorded in the study area are located on fault elements. This gives an indication that the delineated fault elements are active.

The influence of temperature‐dependent viscosity on lava flow dynamics

AbstractMany studies have investigated how channels and tubes form within basaltic flows. The partitioning of a broad lava flow into narrow regions of enhanced flow velocity (which we refer to as preferred pathways) can affect lava emplacement, and allow flows to reach great lengths on Earth and other planets. In this study, we investigate the role that a dynamic instability, driven by large changes in viscosity due to small changes in temperature, can play in the formation and propagation of low‐viscosity preferred pathways. We use a fluid dynamics‐based model of laminar lava flow emplacement that examines this process exclusively. Analysis of this model shows that preferred pathways will initiate when the temperature dependence of the lava's viscosity is sufficiently strong. If a preferred pathway develops, it will form and stabilize over a distance that reflects the competition between the cooling rate through the flow's surfaces and the flow velocity within the preferred pathway. Using velocity and cooling rates of typical basaltic flows on Earth, this model is able to produce preferred pathways within lava flows with reasonable dimensions and timescales. The model also fails to produce such pathways in situations where tubes and channels are not found in nature (e.g., in basalt sheet flows and silicic flows &lt; 1 km in length). These results are sufficiently positive to demonstrate that this thermodynamic instability may play a role in the formation and propagation of preferred pathways within some flows, and thus merit further investigation.

Delineating active faults by using integrated geophysical data at northeastern part of Cairo, Egypt

Geophysical techniques such as gravity, magnetic and seismology are perfect tools for detecting subsurface structures of local, regional as well as of global scales. The study of the earthquake records can be used for differentiating the active and non active fault elements. In the current study more than 2200 land magnetic stations have been measured by using two proton magnetometers. The data is corrected for diurnal variations and then reduced by IGRF. The corrected data have been interpreted by different techniques after filtering the data to separate shallow sources (basaltic sheet) from the deep sources (basement complex). Both Euler deconvolution and 3-D magnetic modeling have been carried out. The results of our interpretation have indicated that the depth to the upper surface of basaltic sheet ranges from less than 10–600m, depth to the lower surface ranges from 60 to 750m while the thickness of the basaltic sheet varies from less than 10–450m. Moreover, gravity measurements have been conducted at the 2200 stations using a CG-3 gravimeter. The measured values are corrected to construct a Bouguer anomaly map. The least squares technique is then applied for regional residual separation. The third order of least squares is found to be the most suitable to separate the residual anomalies from the regional one. The resultant third order residual gravity map is used to delineate the structural fault systems of different characteristic trends. The trends are a NW–SE trend parallel to that of Gulf of Suez, a NE–SW trend parallel to the Gulf of Aqaba and an E–W trend parallel to the trend of Mediterranean Sea. Taking seismological records into consideration, it is found that most of 24 earthquake events recorded in the study area are located on fault elements. This gives an indication that the delineated fault elements are active.

Experimental Study on Flexural of RC Beams Strengthened with Basaltic Fiber Sheets

The bending performance test on one ordinary reinforced concrete beam and six RC beams strengthened with basalt fiber sheets(BFRP) is carried out, and the bending performance of the RC beams strengthened with BFRP is analyzed. The experimental results show that BFRP improves the bending performance of the beam. Pasting one layer,two layers or three layers of BFRP, The ultimate strength RC beams were increased by 29%, 56% and 78%. Basalt fiber sheets and concrete beams can work better together and play an effective role in reinforcement.