Structural setup of Ras Banas area,Red Sea,Egypt, as inferred from aeromagnetic data

This study deals with the evaluation of the structural setup of the Ras Banas area on the northwestern part of the Red Sea by using magnetic data. Different analyzing techniques were applied to achieve this goal including regional-residual separation, trend analysis, depth estimation, Euler deconvolution, horizontal gradient, analytic signal, and magnetic modeling. The results of these techniques were used to construct a deep-seated structural feature map.Lineament analysis indicates that the area was mainly affected by the NW, WNW, and NE tectonic trends. The magnetic modeling was performed along four profiles supported by Euler deconvolution, horizontal gradient, and analytic signal profiles. The modeled profiles show that the basement rocks composed of uplifted and down-faulted blocks at different depths as well as step-like structure. The basement rocks seem to be acidic in nature intruded by basic/ultrabasic dikes. Generally, the magnetic susceptibility ranges from 0.0003 to 0.04 cgs indicating acidic to basic/ultrabasic rock composition. The basement relief map shows an irregular basement surface, which varies greatly in depth from 1 to 5.6 km below sea level. The deep-seated structure map shows that the basement was highly affected by two main fault trends in the NW and NNE directions. The NW trending structures were intersected by younger left lateral NNE transform faults. These cross-faults dissect the area into a number of alternated and elongated blocks.     

Integrated potential field study on the subsurface structural characterization of the area North Bahariya Oasis, Western Desert, Egypt

The present study aims mainly to delineate and outline the regional subsurface structural and tectonic framework of the buried basement rocks of Abu El Gharadig Basin, Northern Western Desert, Egypt. The potential field data (Bouguer gravity and total intensity aeromagnetic maps) carried out in the Abu El Gharadig Basin had been analyzed together with other geophysical and geological studies. The execution of this study is initiated by transformation of the total intensity aeromagnetic data to the reduced to pole (RTP) magnetic map. This is followed by applying several transformation techniques and various filtering processes through qualitative and quantitative analyses on both of the gravity and magnetic data. These techniques include the qualitative interpretation of gravity, total intensity magnetic and RTP magnetic maps. Regional–residual separation is carried out using the power spectrum. Also, the analytic signal and second vertical derivative techniques are applied to delineate the hidden anomalies. Aeromagnetic anomalies in the area reflect significant features on the basement tectonics, on the deep-seated structures and on the shallow-seated ones. Major faults and intrusions in the area are indicated to be mainly along the NE–SW, NW–SE, ENE–WSW and E–W directions. The Bouguer gravity map indicates major basement fracturing, as well as variations in the sedimentary basins and ridges and subsequent tectonic disturbances. The most obvious anomalous trends on the gravity map, based on their frequencies and amplitudes, are along the NE–SW, ENE–WSW, E–W and NW–SE trends. The main of Abu EL Gharadig Basin depositional center does not show sharp variations, because of the homogeneity of the marine rocks and the great basement depths.     

Aeromagnetic study of buried basement structures and lineaments of Sahel region (Eastern Tunisia,North Africa)

This study presents original results regarding the use of aeromagnetic to explore deep subsurface structuring in southern part of Tunisian Sahel petroleum province (Eastern Tunisia, North Africa). Several filters and techniques were applied to the total magnetic intensity (TMI) grid. First, an adequate reduce to the pole (RTP) grid was generated. The RTP map shows 17 positive and negative anomalies associated with short- and long-wavelength amplitude anomalies. Positive anomalies correspond to high magnetic basement structures estimated from seismic lines in the area. Circular anomalies are also distinguished locally and can be explained by Cretaceous magmatic rocks recognized in numerous petroleum wells. Second, specific qualitative and quantitative filters (e.g., residual-regional separation, horizontal tilt angle (TDX), tilt angle (TILT), total horizontal derivative of tilt angle (THDTILT)) were applied to elucidate the form and the extent of buried magnetic anomalies and lineaments. The resulting deep structural map revealed the presence of NW-SE, N-S, and E-W regional magnetic basement structures and lineaments and a regional tectonic node surrounding Henchir Keskes-Agareb-Mahres-Hachichina area. Two magnetic inversion models calculated across the study area highlight west to east crustal thinning trend and permit depth to basement estimation. These results are valuable for future conventional and unconventional petroleum exploration in this underexplored southern part of Sahel plain.     

Delineation the active subsurface structures at Fayoum-Cairo district, Egypt, using magnetic and magnetotelluric tools

In this work, we present a reconnaissance study to elucidate and delineate subsurface fault structures for an active tectonics area that lies between Cairo and El Fayoum provinces and consider major sources of seismicity in Egypt. Well logging, aeromagnetic, land magnetic, and magnetotelluric data have been used. The well-logging data were used for several drilled wells along W–E direction. The magnetic data were analyzed using trend analysis, 3D magnetic modeling, and Werner deconvolution techniques. The magnetotelluric data were interpreted using 2D (TM–TE) modeling techniques. The results show that there are eight major fault structures having E–W, N–S, and NW–SE directions. These faults extend downward for about 20 km at the Dahshour and Qatrani areas. The epicenter sources of the earthquakes are clustering around the intersections of these structures. The Kattaniya horst structure has been interpreted as a regional structure that exceeds the limits previously determined by geologists. The depth to this horst reaches about 1.8 km at the NW and more than 4.3 km at the southern parts. The interpreted values of magnetic susceptibility at the horst zone indicate that they are ultrabasic/basic intrusion bodies.     

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.     

Gravity and magnetic data analysis of block-35, Jiza' basin,Eastern Yemen

The Jiza' basin is located in the eastern part of Yemen, trending generally in the E–W direction. It is filled with Middle Jurassic to recent sediments, which increase in thickness approximately from 3,000 m to more than 9,000 m. In this study, block-35 of this sedimentary basin is selected to detect the major subsurface geological and structural features characterizing this basin and controlling its hydrocarbon potentials. To achieve these goals, the available detailed gravity and magnetic data, scale 1:100,000, were intensively subjected to different kinds of processing and interpretation steps. Also, the available seismic reflection sections and deep wells data were used to confirm the interpretation. The results indicated three average depth levels; 12.5, 2.4, and 0.65 km for the deep, intermediate, and shallow gravity sources and 5.1 and 0.65 km for the deep and shallow magnetic sources. Accordingly, the residual and regional anomaly maps were constructed. These maps revealed a number of high and low structures (horsts and grabens and half grabens), ranging in depth from 0.5 km to less than 4.5 km and trending mainly in the ENE, NW, and NE directions. However, the analytical signal for both gravity and magnetic data also showed locations, dimensions, and approximate depths of the shallow and near surface anomaly sources. The interpretation of the gravity and magnetic anomalies in the area indicated that the NW, NNW, ENE, and NE trends characterize the shallow to deep gravity anomaly sources; however, the NE, NW, and NNE trends characterize the magnetic anomaly sources, mainly the basement. Two-dimensional geologic models were also constructed for three long gravity anomaly profiles that confirmed and tied with the available deep wells data and previously interpreted seismic sections. These models show the basement surface and the overlying sedimentary section as well as the associated faults.     

Interpretation of high resolution aeromagnetic data over southern Benue Trough,southeastern Nigeria

High resolution airborne magnetic data of parts of the southern Benue Trough were digitally processed and analyzed in order to estimate the depth of magnetic sources and to map the distribution and orientation of subsurface structural features. Enhancement techniques applied include, reduction to pole/equator (RTP/RTE), first and second vertical derivatives, horizontal gradients and analytic signal. Results from these procedures show that at least 40% of the sedimentary basin contain shallow (<200 m) magmatic bodies, which in most cases are intermediate to mafic intrusive and hyperbysal rocks, and may occur as sills, dikes or batholiths. Magnetic lineaments with a predominant NE–SW trend appear to be more densely distributed around the basement rocks of the Oban Hills and metamorphosed rocks around the Workum Hills. 3D standard Euler deconvolution and Source Parameter Imaging (SPI ^TM) techniques were employed for depth estimation. Results from the two methods show similar depth estimates. The maximum depth to basement values for 3D Euler and SPI are 4.40 and 4.85 km with mean depths of 0.42 and 0.37 km, respectively. Results of 2D modelling of magnetic profiles drawn perpendicular to major anomalies in the study area reveal the existence of deep seated faults which may have controlled the emplacement of intrusive bodies in the basin. The abundance of intrusive bodies in the study area renders this part of the southern Nigerian sedimentary basins unattractive for petroleum exploration. However, the area possesses high potential for large accumulation of base metal mineralization.     

Geodynamics and underlying bedrock of the magnetically active crust layer of the Lut block,Eastern Iran

The Curie point depth map of Eastern Iran was constituted from spectral analysis of the aeromagnetic data. The reduction to pole (RTP) was applied to the magnetic anomaly data. The Curie point depth values from 165 overlapping blocks, 100 × 100 km in size, have been estimated. The Curie point depth method provides a relationship between the 2-D FFT power spectrum of the magnetic anomalies and the depth of magnetic sources by transforming the spatial data into the frequency domain. The centroid and top depth of the magnetic sources (respectively Z₀ and Z_t) is calculated from radially averaged log power spectrum for each block. Finally, the Curie point depth of Eastern Iran is obtained by Z_b = 2Z₀–Z_t. The highest value of 24 km is located in eastern and western boundaries of the Lut block, and the lowest value of 12 km is located at north of study area. The shallow depths in the Curie-point depth map are well correlated with the young volcanic areas and geothermal potential fields. Geothermal gradient ranging from 24 to 45°C/km. The deduced thermal structure in eastern Iran has a relationship with orogenic collapse associated with delamination of thickened lithospheric root between the Lut and Afghan continental blocks.     

The Diamantina River ring feature,Winton region,western Queensland

The Diamantina ～120 km-diameter ring feature, a unique feature in western Queensland, is manifested by a near-360° circular drainage pattern, radial creeks and a coincident radiometric K–Th–U pattern. The structure has been studied in the context of an investigation of the nature and origin of Australian circular structures. Geophysical signatures, including total magnetic intensity (TMI), gravity and seismic reflection transect data from the region of the ring feature are examined to help test the origin of the structure. A western subdued TMI arc with a ～110 km diameter is offset by ～30 km eastward from the western rim of the drainage ring. Bouguer anomaly data show a gravity low near the centre of the ring structure, but no outer circular pattern. Two recent seismic transects indicate a moderately reflective to weakly reflective crust below flat lying strata of the Jurassic–Cretaceous Eromanga and Permian–Triassic Galilee basins, and above a usually well-defined ～39–45 km-deep Moho. An approximately ～100 km-wide seismically non-reflective to weakly reflective zone overlapping the Diamantina ring feature separates crust of different seismic reflection character to either side. The nature of the seismic non-reflective crust is unknown. A potential interpretation of the ring structure in terms of asteroid impact cannot be confirmed or rejected given the present state of knowledge, owing to (1) the near-30 km depth of the seismically non-reflective zone along the transects; and (2) the shift of the TMI part ring zone relative to the geomorphic expression of the Diamantina ring feature. A test of the nature and origin of the Diamantina ring feature requires a cored drill hole near the centre of the TMI ring structure.     

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.     

Aeromagnetic data interpretation of east Qattara Depression,Northwest Desert,Egypt

The study area is located at the east of Qattara Depression at the north of the Western Desert of Egypt. The study area contains Abu Gharadig basin, which is the most petroliferous basin in the Egyptian Western Desert. Only three exploratory wells are presented in the study area, showing a thick sediment section overlying basement rocks. Magnetic data have been frequently used in geophysical exploration. Aeromagnetic data are mainly utilized to estimate the depth to the magnetic basement as well as to delineate the possible structures of the study area. The depth to magnetic basement has been estimated using the analytical solution of exponential equations obtained from the Fourier transformation of magnetic data, assuming multi-prisms. The depths obtained from this technique vary from 0.70 to 2.91 km with an average depth of 2.08 km. Local phase filters have been mainly used as edges detector where the possible occurrences structures can be delineated. Hyperbolic tilt angle, second-order tilt angle, and normalized total horizontal derivative (TDX) provide the best results for delineating the possible structures, showing the possible contacts within the basement of the study area. The edge enhancement filters show that the study area has been affected by different structural trends taking E-W, NE-SW, NNE-SSW, N-S, and ENE-WSW directions.     

Exploration for iron ore in Agbado-Okudu,Kogi State,Nigeria

This report details the result of geophysical exploration for iron ore; which involved vertical magnetic intensity (?Z) and gravity measurements, to delineate the geometry and depth extent of the deposit and acquiring quantitative and qualitative information for pre-drilling purposes in Agbado-Okudu. It is located about 3 km from Jakura along Lokoja-Jakura marble quarry and within low latitude precambrian basement complex district of Kogi State, Nigeria. A total of 517 magnetic measurement points along 16 traverses and 330 gravity reading along 11 profiles on the deposit in northeast–southwest azimuth were undertaken. The magnetic and gravity data enhancement involved linear regression curve fitting and fast Fourier transform, which were used to construct residual magnetic (RM) and gravity (RG) anomalies, analytic signal amplitude, Euler deconvolution at varying spectral indices (SI), power spectrum, and source parameter image (SPI), using the submenu of Geosoft Oasis Montaj software. Interpretation of the RM and RG anomalies revealed a primary causative body which perfectly correlates the positive anomalies and iron ore deposit, in form of a horizontal or gently dipping dyke with strike length of 600 m and average width of 110–130 m, within the gneiss complex in the north and trending south of the area. A secondary causative body associated with the negative anomalies and inferred as a vertical/near vertical thin sheet striking northeast–southwest coincided with the granitic and quartzitic intrusion. The NW–SE and E–W lineament trend conformed Kibarian and Liberian orogeny cycles of generally known structural trends in Nigeria, which shows that the iron ore deposit is structurally controlled. Depths to sources were estimated within range ≤ 2–24 m and 37.5–60 m, regarded as shallow and relatively deep depths, respectively. Ten vertical boreholes ranging in depth between 50 and 100 m are recommended, five of which require a priority attention to ascertain the thickness of the primary causative body.     

Molybdenum deposits in the eastern Qinling,central China: constraints on the geodynamics

More than a dozen molybdenum prospects, distributed within a zone about 200 km long and 20 km wide, have been discovered in the Eastern Qinling orogenic belt, central China. These deposits are mainly hosted within small, dominantly granoporphyritic and quartz monzonitic intrusions of Cretaceous age. They can be classified into five groups based on spatial relationships between the ores and intrusions: porphyry-type, transitional-type (between porphyry and skarn), skarn-type, vent breccia-type, and hydrothermal vein-type Mo deposits. Regional geologic relations and deep-seated structures define the presence of the Luanchuan syncline, an EW-striking west-dipping depression located beneath the Mo-bearing metallogenic zone. Because the axis of the syncline is west-dipping in the study area and the crust overlying it is thickened, the stress is inhomogeneous, resulting in a S–N compressive stress in the deep crust and development of a set of NE-oriented extension-shear faults. These faults are superimposed on the W–E-striking deep-seated faults parallel to the ancient continental margin. The two groups form a chequerboard-like assemblage of deep-seated faults, providing channels for ascending ore fluids derived from crust–mantle interaction and space for subsequent ore precipitation. These faults controlled the emplacement of a series of intermediate-acid granite magmas and also contributed significantly to the distribution of the various Eastern Qinling ore deposits.     

Subsurface structural trends of the offshore Nile Delta area, Egypt: evidences from gravity and magnetic data

Subsurface structural trends and tectonics affecting the offshore Nile Delta area, Egypt, have been studied through the interpretations of gravity and magnetic data. Reduced to the pole, regional–residual separation, Tilt derivative and Euler deconvolution techniques are applied for the processing and interpretations of the magnetic and gravity data. The average depth of the sedimentary cover, estimated from the two-dimensional power spectrum technique ranges between 8 km and 13 km. The interpretation of the gravity and magnetic data indicates that the study area is affected by many subsurface structural trends. The NW–SE is the major trend related to El-Temsah and Misfaq-Bardwil trend. The NE–SW direction is the second dominant trend, related to the Rosetta trend. Other trends defined through the interpretation of gravity and magnetic data include: the N–S direction, related to the Baltim fault trend, the E–W direction, related to the Neogene hinge line and the NNE–SSW related to the Gulf of Aqaba. Accessory trends include the ENE–WSW, WNW–ESE and finally the NNW–SSW.     

The use of magnetic and geo-electrical data to delineate the subsurface structures and groundwater potentiality in Southeastern Sinai, Egypt

The study area is located in the southern part of Sinai Peninsula. This study was done to delineate the subsurface structure of the basement rocks affecting the groundwater potentiality in the study area and to perform the lateral and vertical variations in the subsurface lithologic properties. To achieve these, a high-resolution total intensity magnetic map and geo-electrical survey were acquired. Two-dimensional power spectrum, analytical signal, and Euler deconvolution techniques are applied on magnetic data. The geo-electric data interpretations concluded that, the study area can be classified into five units of sediments arranged as: (1) the top surficial layer of dry sand and gravels; (2) the second layer of silty sand layer with thickness ranging from 5 to 35 m; (3) the third layer of dry sand with thickness ranging from 5 to 130 m; (4) the fourth layer composed of saturated sand which was considered as the water-bearing zone of the investigated interval, its thickness ranges between 50m and more than 200 m; (5) the fifth layer is interpreted as basement rocks. The depth to the basement surface has an average value of 156 m at the eastern side and 758 m at the western side of the study area. This area is characterized by a graben structure bounded by major faults striking in the NW–SE direction and is considered one of the most promising regions for water resources in Sinai.     

Delineation of saline groundwater and sea water intrusion zones using transient electromagnetic (TEM) method, Wadi Thuwal area, Saudi Arabia

In the coastal western part of Saudi Arabia at Thuwal area located close from the Red Sea, the shallow groundwater specific electrical conductivities measured at the drill holes range from 6 to 13 mS/cm. In order to study the origin of this salinity, a good knowledge is required of the aquifer geometry with depth. Ninety nine transient electromagnetic (TEM) soundings were carried out over an area of about 100 km². From the TEM profiles, a conductive substratum with a resistivity of 1–13 Ωm was identified at most of the sites at depth ranging from 50 to 150 m. This substratum is related to Oligocene–Miocene sediments (Shumaysi Formation) which are mainly red clay-rich formation containing brines at coastal zones. Clayey sediments are more likely present in the southeastern part and along the faults that run NE–SW across the study area and parallel to the Quaternary volcanic which runs NW–SE. The study demonstrated the effectiveness of the TEM sounding method to map conductive zones.     

Partitioning of convergence in Northwest Sub-Himalaya: estimation of late Quaternary uplift and convergence rates across the Kangra reentrant,North India

The Kangra reentrant constitutes a ~ 80-km-wide zone of fold-thrust belt made of Cenozoic strata of the foreland basin in NW Sub-Himalaya. Earlier workers estimated the total long-term shortening rate of 14 ± 2 mm/year by balanced cross-section between the Main Boundary Thrust and the Himalayan Frontal Thrust. Geologically estimated rate is nearly consistent with the GPS-derived slip rate of 14 ± 1 mm/year. There are active faults developed within 4–8 km depth of the Sub-Himalayan fold-thrust belt of the reentrant. Dating the strath surfaces of the abandoned fluvial terraces and fans above the thrust faults, the uplift (bedrock incision) rates are computed. The dips of thrust faults are measured in field and from available seismic (depth) profiles. From the acquired data, late Quaternary shortening rates on the Jawalamukhi Thrust (JT), the Soan Thrust (ST) and the Himalayan Frontal Thrust (HFT) are estimated. The shortening rates on the JT are 3.5–4.2 mm/year over a period 32–30 ka. The ST yields a shortening rate of 3.0 mm/year for 29 ka. The corresponding shortening and slip rates estimated on the HFT are 6.0 and 6.9 mm/year during a period 42 ka. On the back thrust of Janauri Anticline, the shortening and slip rates are 2.0 and 2.2 mm/year, respectively, for the same period. The results constrained the shortening to be distributed largely across a 50-km-wide zone between the JT and the HFT. The emergence of surface rupture of a great and mega earthquakes recorded on the reactivated HFT implies ≥100 km width of the rupture. The ruptures of large earthquakes, like the 1905 Kangra and 2005 Kashmir, remained restricted to the hinterland. The present study indicates that the high magnitude earthquakes can occur between the locking line and the active thrusts.     

In situ stresses and natural fractures in the Northern Perth Basin,Australia

Present-day stress orientations in the Northern Perth Basin have been inferred from borehole breakouts and drilling-induced tensile fractures observed on image logs from eight wells. Stress indicators from these wells give an east – west maximum horizontal stress orientation, consistent with stress-field modelling of the Indo-Australian Plate. Previous interpretations using dipmeter logs indicated anomalous north-directed maximum horizontal stress orientations. However, higher-quality image logs indicate a consistent maximum horizontal stress orientation, perpendicular to dominant north – south and northwest – southeast fault trends in the basin. Vertical stress was calculated from density logs at 21.5 MPa at 1 km depth. Minimum horizontal stress values, estimated from leak-off tests, range from 7.4 MPa at 0.4 km to 21.0 MPa at 0.8 km depth: the greatest values are in excess of the vertical stress. The maximum horizontal stress magnitude was constrained using the relationship between the minimum and maximum horizontal stresses; it ranges from 8.7 MPa at 0.4 km to 21.3 MPa at 1 km depth. These stress magnitudes and evidence of neotectonic reverse faulting indicate a transitional reverse fault to strike-slip fault-stress regime. Two natural fracture sets were interpreted from image logs: (i) a north- to northwest-striking set; and (ii) an east-striking set. The first set is parallel to adjacent north- to northwest-striking faults in the Northern Perth Basin. Several east-striking faults are evident in seismic data, and wells adjacent to east-striking faults exhibit the second east-striking set. Hence, natural fractures are subparallel to seismically resolved faults. Fractures optimally oriented to be critically stressed in the present-day stress regime were probably the cause of fluid losses during drilling. Pre-existing north- to northwest -striking faults that dip moderately have potential for reactivation within the present-day stress regime. Faults that strike north to northwest and have subvertical dips will not reactivate. The east-striking faults and fractures are not critically stressed for reactivation in the Northern Perth Basin.     

Application of spectral analysis technique on ground magnetic data to calculate the Curie depth point of the eastern shore of the Gulf of Suez,Egypt

The bottom of the magnetized crust determined from the spectral analysis of magnetic anomaly is interpreted as a level of the Curie point isotherm. A spectral analysis technique was used to estimate the depth of the magnetic anomalies sources (Curie point depth analysis) of the eastern shore of the Gulf of Suez, Egypt. The depth to the tops and centers of the magnetic anomalies are calculated by azimuthally averaged power spectrum method for the whole area. The results obtained suggests from this study showed that the average depth to the top of the crustal block ranges between 1.15 and 1.9 km, whereas the average depth to the center of the deepest crustal block ranges between 9.1 and 12.7 km. Curie point depths in the study area range between 14.5 km in the northwestern part of the study area and 26 km in the southeastern part of the study area. The results imply a high geothermal gradient (34.7 °C/km) and corresponding high heat flow value (72.87 mW/m²) in the northwestern part of the study area. The southeastern part of the study area displays a low geothermal gradient (24.26 °C/km) and low heat flow value (50.9 mW/m²). These results are consistent with the existence of the possible promising geothermal reservoir in the eastern shore of the Gulf of Suez especially at Hammam Faraun area.     

高精度磁测技术在西成铅锌矿勘探中的应用

近年来,甘肃西成铅锌矿的勘探向周边地区扩展,高精度磁法测量发挥了一定作用。利用化极磁异常垂向一阶导数和归一化总水平导数垂向导数,推断出5处地质体边界和4条断裂。根据该区地质和矿产分布特征,推测矿体主要分布于黑云母石英片岩向大理岩的接触或过渡地带,对应中泥盆统安家岔组厂坝层D2a1条带状大理岩。根据化极磁异常和该区构造,结合化探圈定出与成矿有关的4个靶区,这些靶区与Pb、Zn化探异常对应,可见若干矿化点。选取靶区内一磁测剖面进行反演,反演结果说明矿体向北西倾斜。经钻孔验证,已在不同深度见矿,证明了靶区的找矿潜力。