Aerospectrometric and aeromagnetic characteristics associated Nb–Ta–Sn mineralization, G. Nuweibi albite granite Central Eastern Desert, Egypt     

Sami Hamed Abd El Nabi 《Arabian Journal of Geosciences》2011,5(5):971-983

A geophysical signature associated with Nb–Ta–Sn mineralization of G. (G. : abbreviation to word Gebel which means mountain in Arabic) Nuweibi area, located the Central Eastern Desert of Egypt is presented. This signature was established by an integration of airborne gamma ray spectrometric and magnetic data. Variations seen in the gamma ray spectrometric data are used as a base to study the three granitic suites: younger-, albite-, and older granites in G. Nuweibi area. Graphical techniques such as frequency histograms and box-plots are used to visualize the shape of the distribution and determine the anomaly thresholds of the three radioelements eU, eTh, and K% data in these granitic suites. The box-plot graphical representations and calculations made on data sets indicate that no samples have eU values above the thresholds, i.e., no outliers representing values of the box-plots. Nuweibi albite granite is associated with a gamma ray response that includes the strongest eU, eTh, K%, and eTh/K ratio anomalies in the study area. K–eTh plot shows that the albite granite has a higher eTh concentration than the older and younger granites. The increase in K concentration and raise in Th/K ratio of Nuweibi albite granite points to unusual geological processes leading to mineralization and reflects the highly fractionated nature of the magma which results in thorium enrichment. This also reflects that K alteration associated with Nb–Ta–Sn mineralization is both poorly focused spatially and very much weaker than observed in any other mineralizing districts. The distribution of magnetic sources and their locations and depths in the study region are determined by Euler deconvolution and analytical signal techniques. Good clustering of Euler solutions were obtained using SI?=?0.5 and SI?=?1.0 for most of the features in the area under consideration. The solutions obtained have shown magnetic sources which can be related to the impact structure whose depths varies between ground surface to 1.66 km. The analytical signal revealed that the metamorphosed basic rocks (mainly olivine metagabbro), serpentinite and dyke bodies are the main sources of high magnetic anomalies, particularly within the area east G. Nuweibi region.  相似文献   

The geometric configuration of the newly discovered Abu Deleig sedimentary sub-basin,Central Sudan,using remote sensing,structural analysis,and geophysical survey     

Abdalla E. M. Elsheikh  Khalid A. Elsayed Zeinelabdein  Sami O. H. El Khidir  Abdalla E. Ibrahim 《Arabian Journal of Geosciences》2014,7(2):789-797

Abu Deleig area is a transitional area between the Butana basement terrain to the east; and the Khartoum and Shendi sedimentary basins to the west and northwest directions, respectively. The existence of sedimentary basins within this region of Sudan was previously unknown. Landsat images have been used for delineation of lineaments and drainage system, followed by a structural analysis and geophysical investigations including gravity and resistivity methods. The interpretation of the remotely sensed data revealed that the drainage pattern is structurally controlled. The structural analysis defined the trends of the shear and tensional fractures. The structural analysis revealed that Wadi Al Hawad is the southern continuation of the Keraf Shear Zone. The related minor fractures in a NE–SW direction exhibit normal faults governing the geometry of the Abu Deleig sub-basin. The geophysical investigations confirmed the findings of structural analysis and portrayed the subsurface geometry of the sub-basin. The newly discovered sub-basin has a prism-like shape with its apex occurring at Abu Deleig town and extends to 40 km in NW direction. The depth to the basement increases from 20 m at Abu Deleig in step form to more than 300 m, where it is linked with the Shendi Basin in the northwestern part. The results of this study, however, did not confirm any link of Abu Deleig sub-basin with Atbara Basin to the NE or Khartoum Basin to the west as have been previously suggested.  相似文献   

Sunspots: An overview     

Sami K. Solanki 《Astronomy and Astrophysics Review》2003,11(2-3):153-286

Sunspots are the most readily visible manifestations of solar magnetic field concentrations and of their interaction with the Sun's plasma. Although sunspots have been extensively studied for almost 400 years and their magnetic nature has been known since 1908, our understanding of a number of their basic properties is still evolving, with the last decades producing considerable advances. In the present review I outline our current empirical knowledge and physical understanding of these fascinating structures. I concentrate on the internal structure of sunspots, in particular their magnetic and thermal properties and on some of their dynamical aspects. Received 27 September 2002 / Published online 3 March 2003  相似文献   

European provenance of the Numidian Flysch in northern Tunisia     

Christine Fildes  Dorrik Stow  Sami Riahi  Mohamed Soussi  Urval Patel  J. Andy Milton  Stuart Marsh 《地学学报》2010,22(2):94-102

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Basin shape and sediment architecture in the Gun Supersequence: A strike‐slip model for Pb–Zn–Ag ore genesis at Mt Isa     

P. N. Southgate  D. L. Scott  T. T. Sami  J. Domagala  M. J. Jackson  N. P. James 《Australian Journal of Earth Sciences》2013,60(3):509-531

Sequence‐stratigraphic correlations provide a better understanding of sediment architecture in the Mt Isa and lower McNamara Groups of northern Australia. Sediments record deposition in a marine environment on a broad southeast‐facing ramp that extended from the Murphy Inlier in the northwest to the Gorge Creek, Saint Paul and Rufous Fault Zones in the southeast. Depositional systems prograded in a southeasterly direction. Shoreline siliciclastic facies belts initially formed on the western and northern parts of the ramp, deeper water basinal facies occurred to the east and south. The general absence of shoreline facies throughout the Mt Isa Group suggests that depositional systems originally extended further to the east and probably crossed the Kalkadoon‐Leichhardt Block. Fourteen, regionally correlatable fourth‐order sequences, each with a duration of approximately one million years, are identified in the 1670–1655 Ma Gun Supersequence. Stratal correlations of fourth‐order sequences and attendant facies belts resolve a stratigraphic architecture dominated by times of paired subsidence and uplift. This architecture is most consistent with sinistral strike‐slip tectonism along north‐northeast‐oriented structures with dilational jogs along northwest structures as the primary driver for accommodation. Although reactivated during deformation, the ancestral northwest‐trending May Downs, Twenty Nine Mile, Painted Rocks, Transmitter, Redie Creek and Termite Range Fault Zones are interpreted as the principal synsedimentary growth structures. Sinistral strike‐slip resulted in a zone of long‐lived dilation to the north of the May Downs/Twenty Nine Mile and Gorge Creek Fault Zones and a major basin depocentre in the broad southeast‐facing ramp. Subordinate depocentres also developed on the northern side of the ancestral Redie Creek and Termite Range fault zones. Transfer of strike‐slip movement to the east produced restraining or compressive regions, localising areas of uplift and the generation of local unconformities. Northwest‐ and north‐northeast‐oriented magnetic anomalies to the south and west of Mt Isa, identify basement heterogeneities. Basement to the south and west of these anomalies is interpreted to mark intrabasin siliciclastic provenance areas in the Gun depositional system. Pb–Zn–Ag deposits of the Mt Isa valley are interpreted as occurring in a major basin depocentre in response to a renewed phase of paired uplift and subsidence in late Gun time (approximately 1656 Ma). This event is interpreted to have synchronously created accommodation for sediments that host the Mt Isa deposit, while focusing topographically and thermobarically driven basinal fluids into the zone of dilation.  相似文献   

Mesozoic and Cenozoic vertical movements in the Atlas system (Algeria, Morocco, Tunisia): An overview   总被引：5，自引：0，他引：5  

Dominique Frizon de Lamotte  Pascale Leturmy  Sami Khomsi  Omar Saddiqi  André Michard 《Tectonophysics》2009,475(1):9-28

The E-W trending Atlas System of Maghreb consists of weakly shortened, intra-continental fold belts associated with plateau areas (“Mesetas”), extending between the south-westernmost branch of the Mediterranean Alpine Belt (Rif-Tell) and the Sahara Platform. Although the Atlas system has been erected contemporaneously from Morocco to Algeria and Tunisia during the Middle Eocene to Recent, it displays a conspicuous longitudinal asymmetry, with i) Paleozoic outcrops restricted to its western part; ii) highest elevation occurring in the west, both in the Atlas System and its foreland (Anti-Atlas); iii) low elevation corridors (e.g. Hodna) and depressed foreland (Tunisian Chotts and Sahel area) in the east. We analyse the origin of these striking contrasts in relation with i) the Variscan heritage; ii) crustal vertical movements during the Mesozoic; iii) crustal shortening during the Cenozoic and finally, iv) the occurrence of a Miocene-Quaternary hot mantle anomaly in the west. The Maghreb lithosphere was affected by the Variscan orogeny, and thus thickened only in its western part. During the Late Permian-Triassic, a paleo-high formed in the west between the Central Atlantic and Alpine Tethys rift systems, giving birth to the emergent/poorly subsident West Moroccan Arch. During the late Middle Jurassic-Early Cretaceous, Morocco and western Algeria were dominantly emergent whereas rifting lasted on in eastern Algeria and Tunisia. We ascribe the uplift of the western regions to thermal doming, consistent with the Late Jurassic and Barremian gabbroic magmatism observed there. After the widespread transgression of the high stand Cenomanian-Turonian seas, the inversion of the Atlas System began during the Senonian as a consequence of the Africa-Eurasia convergence. Erosion affected three ENE-trending uplifted areas of NW Africa, which we consider as lithospheric anticlines related to the incipient Africa-Europe convergence. In contrast, in eastern Algeria and Tunisia a NW-trending rift system developed contemporaneously (Sirt rifting), normal to the general trend of the Atlas System. The general inversion and orogenesis of the Atlas System occurred during two distinct episodes, Middle-Late Eocene-Oligocene and Late Miocene-Pliocene, respectively, whereas during the intervening period, the Africa-Europe convergence was mainly accommodated in the Rif-Tell system. Inversion tectonics and crustal thickening may account for the moderate uplift of the eastern Atlas System, not for the high elevation of the western mountain ranges (Middle Atlas, High Atlas, Anti-Atlas). In line with previous authors, we ascribe part of the recent uplift of the latter regions to the occurrence of a NE-trending, high-temperature mantle anomaly, here labelled the Moroccan Hot Line (MHL), which is also marked by a strip of late Miocene-Quaternary alkaline magmatism and significant seismicity.  相似文献   

Magnetothermal condensation modes including the effects of charged dust particles     

Mohsen Shadmehri  Sami Dib 《Monthly notices of the Royal Astronomical Society》2009,395(2):985-990

We study thermal instability in a magnetized and partially ionized plasma with charged dust particles. Our linear analysis shows that the growth rate of the unstable modes in the presence of dust particles strongly depends on the ratio of the cooling rate and the modified dust-cyclotron frequency. If the cooling rate is less than the modified dust-cyclotron frequency, then the growth rate of the condensation modes does not modify due to the existence of the charged dust particles. But, when the cooling rate is greater than (or comparable to) the modified dust-cyclotron frequency, the growth rate of unstable modes increases because of the dust particles. Also, the wavenumber of the perturbations corresponding to the maximum growth rate shifts to the smaller values (larger wavelengths) as the cooling rate becomes larger than the modified dust-cyclotron frequency. We show that the growth rate of the condensation modes increases with the electrical charge of the dust particles.  相似文献   

Understanding the WMAP Results: Low-Order Multipoles and Dust in the Vicinity of the Solar System     

Valeri Dikarev  Oliver Preuß  Sami Solanki  Harald Krüger  Alexander Krivov 《Earth, Moon, and Planets》2008,102(1-4):555-561

Analyses of the cosmic microwave background (CMB) radiation maps produced by the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies not predicted by the standard cosmological theory. It has been suggested that a dust cloud in the vicinity of the Solar system may be the cause for these anomalies. In this paper, the thermal emission by particles from two known interplanetary meteoroid complexes is tested against the CMB maps. Conclusions are drawn based on the geometry of cloud projections onto the WMAP sky whether these clouds are likely to explain the observed anomaly. The smooth background Zodiacal cloud and one of the Taurid meteor complex branches do not explain the WMAP anomaly.  相似文献   

Characterization and Estimation of Geotechnical Variability in Ankara Clay: A Case History     

Sami O. Akbas  Fred H. Kulhawy 《Geotechnical and Geological Engineering》2010,28(5):619-631

An important component in reliability-based design is the geotechnical property variability. Generic estimates are used often, but calibration to a local geologic setting is preferable. In this case history, a methodology is shown that employs local geotechnical data to estimate the total variability, using Ankara Clay for illustration. A literature review is used to estimate the inherent variability, which is modeled as a random field with coefficient of variation (COV) and scale of fluctuation. The resulting inherent variability COVs are much smaller than the generic ranges. Local correlations between various laboratory and field tests and soil strength and compressibility parameters then are developed to quantify the transformation uncertainties. The various sources of uncertainty are combined through a second-moment method to estimate the total geotechnical variability as a function of the test type and correlation used. The results show: (1) the COVs for direct laboratory measurements are significantly smaller than those obtained through correlations, and (2) depending on the geotechnical data available, the local COVs can be very different from the generic guidelines. These could lead to unconservative designs. These issues are illustrated by a simple design example.  相似文献   

Measuring Stellar Differential rotation with asteroseismology     

Laurent Gizon  Sami K. Solanki 《Solar physics》2004,220(2):169-184

The variation of rotation with latitude is poorly known on stars other than the Sun. Several indirect techniques, photometric and spectroscopic, have been used to search for departure from rigid rotation for sufficiently fast rotators. Here we investigate the possibility of measuring stellar differential rotation for solar-type stars through asteroseismology. Rotationally split frequencies of global oscillation provide information about rotation at different latitudes depending on the azimuthal order, m, of the mode of pulsation. We present a method to estimate differential rotation based on the realization that the m = ±1 and m = ±2 components of quadrupole oscillations can be observed simultaneously in asteroseismology. Rotational frequency splittings can be inverted to provide an estimate of the difference in stellar angular velocity between the equator and 45° latitude. The precision of the method, assessed through Monte Carlo simulations, depends on the value of the mean rotation and on the inclination angle between the rotation axis and the line of sight.  相似文献