Subsurface structural features of the basement complex and mineralization zone investigation in the Barramiya area,Eastern Desert of Egypt,using magnetic and gravity data analysis

In the Barramiya area, the majority of gold deposits are generally related with the quartz veins that associated with shear zones cutting the crystalline basement rocks. The quartz vein system is controlled by shear zone and general faults. The present study is to delineate the general faults, shear zones, geological limits, and basement rock relief, using airborne magnetic and gravity data analysis at the Barramiya gold mine and surrounding area, Eastern Desert of Egypt. To achieve our goal, we have applied on magnetic and gravity data the following techniques: reduction to pole (RTP), analytical signal, tilt derivative, total horizontal derivative, 3D Euler deconvolution, downward continuation, and source parameter imagining power spectrum techniques. The analytical signal used to map the types of rock boundaries. Tilt derivative and total horizontal derivative filters helped to delineate fractures and the contact zones of the formations that host the main Barramiya shear zone. 3D Euler deconvolution techniques helped to delineate the fault trends which represented at the following direction: NNE–SSW and NNW–SSE. The average depths of both regional and residual causes have been estimated by applying downward continuation, source parameter imagining, and power spectrum techniques. According to the results of the present study, the depth of the basement rocks is relatively high (~?80-m depth) in the western part of the study area and the basement rocks cropped out in the surface at the rest of the area. Our results are coinciding with the previous geological studies.     

Use of Geophysical and Remote Sensing Data for Assessment of Aquifer Depletion and Related Land Deformation

An integrated approach [field, Interferometric Synthetic Aperture Radar (InSAR), hydrogeology, geodesy, and spatial analysis] was adopted to identify the nature, intensity, and spatial distribution of deformational features (sinkholes, fissures, differential settling) reported over fossil aquifers in arid lands, their controlling factors, and possible remedies. The Lower Mega Aquifer System (area 2 × 10⁶ km²) in central and northern Arabia was used as a test site. Findings suggest that excessive groundwater extraction from the fossil aquifer is the main cause of deformation: (1) deformational features correlated spatially and/or temporally with increased agricultural development and groundwater extraction, and with a decline in water levels and groundwater storage (? 3.7 ± 0.6 km³/year); (2) earthquake events (years 1985–2016; magnitude 1–5) are largely (65% of reported earthquakes) shallow (1–5 km) and increased from 1 event/year in the early 1980s (extraction 1 km³/year), up to 13 events/year in the 1990s (average annual extraction > 6.4 km³). Results indicate that faults played a role in localizing deformation given that deformational sites and InSAR-based high subsidence rates (? 4 to ? 15 mm/year) were largely found within, but not outside of, NW–SE-trending grabens bound by the Kahf fault system. Findings from the analysis of Gravity Recovery and Climate Experiment solutions indicate that sustainable extraction could be attained if groundwater extraction was reduced by 3.5–4 km³/year. This study provides replicable and cost-effective methodologies for optimum utilization of fossil aquifers and for minimizing deformation associated with their use.     

An index to assess the propensity of landfall in Australia of a tropical cyclone

Every year, Australian oceans experience the genesis of many tropical cyclones (TCs). About 40 percent of these make landfall. Because of the enormous difference in impacts between landfalling and non-landfalling TCs on coastal communities, the benefits would be enormous if it were possible to capture early the potentiality of landfall of a TC that has undergone genesis. Published literature identifies many factors such as location, warm sea surface temperature above 26 °C, conditional instability and high relative humidity in the middle troposphere and low vertical wind shear for the genesis of cyclones. Some of these factors could hold information about the potentiality of landfall while a TC is forming. An investigation into these factors actually revealed that a landfall potential index can be developed that can capture the potentiality of making a landfall. An attractive feature of this index is that it uses values at the time and location of genesis, providing a long and useful lead time. Furthermore, it is made into a dimensionless number, which makes for easy comprehension and interpretation.     

The role of geophysical and seismological data in evaluating the subsurface structures and tectonic trends of Nile Delta, Egypt

In the present study, the Bouguer, aeromagnetic, and seismological data analysis for Nile Delta including the Greater Cairo region and its surroundings was used to examine and trace the tectonic framework for some deep-seated faults (mostly normal faults with a small strike–slip component) and their orientation, on which most earthquakes have occurred. The new tilt derivative (TDR) geophysical map and Euler deconvolution presented here can be used to trace the structural relationships and their depth investigations across the entire region. Generally, most of the Euler deconvolution results especially from the gravity map were well coincided with the location of contacts derived by TDR particularly NNW to NS, EW, and NE trended structures. The depths to the gravity or magnetic sources, and the locations of the contacts of density contrast were estimated. Results of the Euler deconvolution method suggested that, in the southeastern part of the area, the basement could be observed to be shallow and has become deeper beneath the northern part. Furthermore, the resulting structural map of this study is well correlated with previous geological and seismological data analyses. At least two sets of predominant faults are suspected, faults with a NNW strike (Clysmic trend) which are particularly felt in the southern portion of the Delta, and some of them give it the shape of a “graben like structure.” Another parallel set of faults, having NE–SW strike (Pelusium trend), was also obvious in the southern part between Cairo and Suez cities (at Abu Zabal area). The evaluated trending faults (NNW–SSE or NE–SW) are intersecting with predominant major WNW–ESE to E–W (Tethys trend) striking faults. These intersections may generate more additional seismic pulses and consequently increase the seismic activity for these structures. However, minor NW (Najd Fault System) is obvious in the TDR magnetic map, whereas less attendance NS (East African trend) structural trends are evident in the TDR gravity map. Moreover, it could be said that the southeastern portion of the Nile Delta (especially the eastern portion of Greater Cairo) is affected by highly tectonic fault systems. Finally, a new tectonic map was also evaluated from the resulting structural map, which helps to quantify different structural patterns (faults and/or contacts), and their relations with the regional tectonic trends are discussed.     

Ocellar lamprophyre dyke bearing mineralization,Wadi Nugrus,Eastern Desert,Egypt: Geology,mineralogy and geochemical implications

The ocellar lamprophyre dyke (ENE-WSW) is recorded at Wadi Nugrus, Eastern Desert, Egypt. It cuts porphyritic biotite granites and varies in thickness from 0.5 to 1.5 m and up to 3 km in length. The lamprophyre dyke has been altered, and it is characterized by porphyritic and panidiomorphic textures with plagioclase, olivine, and augite constituting the porphyritic phase in a fine groundmass of the same composition. Rutile, titanite, apatite, fluorite, graphite, calcite, allanite, autunite and Fe-Ti oxides are accessory minerals. Kaolinite, chlorite and epidote are secondary minerals. Carbonitization and hematitization are common. Rounded to sub-rounded porphyritic and zoned ocelli with radiate or brush-like shapes are generally common and represent physical traps for mineralization. The ocellar features are interpreted to represent the late stage of magmatic segregation or magmatic crystallization involving two immiscible magmatic liquids.     

SARAL/AltiKa Wind and Wave Products: Monitoring,Validation and Assimilation

SARAL/AltiKa surface wind speed (WS) and significant wave height (SWH) measurements are monitored and validated against operational European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric and wave model results in addition to available in-situ observations to access their suitability for various applications, especially SWH data assimilation. The quality of SWH is very high while that of WS is very good except for an underestimation of high wind speeds. The impact of assimilating SWH in the ECMWF Integrated Forecast System was assessed using several numerical experiments. The results show positive impact. Operational assimilation of SWH at ECMWF model is part of the forthcoming model change.     

Orbits of colliding galaxies

A simple, semi-analytic method is developed for obtaining the orbits of galaxies undergoing fast collisions in which the galaxies are represented by Plummer models. The results are found to agree fairly well with those of N-body simulations.A simple formula for obtaining the angle of deflection is deduced. The maximum angle of deflection is 180° forV _p/V _esc(p)=1.00, about 36° forV _p/V _esc(p)=1.50, and about 18° forV _p/V _esc(p)=2.00, whereV _p is the velocity at closest approachp, andV _esc(p) is the parabolic velocity of escape atp. The angle of deflection of a pair of colliding elliptical galaxies without halos is about twice that for a pair of galaxies with halos for the same relative velocity at infinite separation.     

Geologic relationships and mineralization of peralkaline/alkaline granite-syenite of the Zargat Na’am ring complex, Southeastern Desert, Egypt

Tungsten-bearing hydrothermal veins range from tensional veinlets to lodes containing multiple injections of hydrothermal quartz veins. Major composite lodes display greisen alteration envelopes characterized by enrichments in volatiles, K2O, Al2O3, Rb, L…     

A classification of galactic collisions

The effects of collisions between two galaxies on the test galaxy considered are classified as follows — Type A: the changes in the size and mass of the test galaxy are both negligible; Type B: There is significant increase in the size (at least 10%) or decrease in the mass (at least 1%) of the test galaxy or in both; Type C: The test galaxy becomes a component of a double galaxy by tidal capture; Type D: The test galaxy is disrupted by the tidal forces of the field galaxy.The type of collision is given as a function of the distance and speed at closest approach and also as a function of the initial impact parameter and speed at infinite separation of the two galaxies for two density models of the galaxies. Collisions in which the two galaxies do not penetrate each other are generally of type A while slow interpenetrating collisions are generally of type B. Types C and D occur in head-on or nearly head-on collisions if the relative speed of the two galaxies is sufficiently small; the former is favoured if the two galaxies do not differ appreciably in mass and density distribution. If one of the two galaxies is considerably less massive or less centrally concentrated than the other, it will be disrupted in slow close collisions.     

Rock joint modeling using a visco-plastic multilaminate model at constant normal load condition

Rock joints play an important role in the behavior of rock masses under normal and shear loading conditions. Numerical simulation of the behavior of jointed rock masses is not an easy task due to complexities involved in the problem such as joint roughness, joint shear strength, hardening and softening phenomenon and mesh dependency. In this study for modeling purposes, a visco-plastic multilaminate model considering hardening and softening effects has been employed. For providing the necessary data for numerical simulation, a series of laboratory experiments have been carried out on regular tooth-shape asperities made by gypsum, under constant normal load conditions. Shear stress–shear displacement and normal displacement–shear displacement of artificial joint specimens are simulated using the proposed numerical model at constant normal load condition (CNL). The results indicate the capability of the model for simulating rock joints behavior in both strength and deformation field. Although the numerical model has been developed for simulating the behavior of artificial joints, the concept of the method can also be used for natural rock joints.