GEOSCIENCES
Year:2005 | Volume:14 | Issue:54|Papers Count:13

This article deals with a brief history of inversion of striated fault plane in order to deduce the state and direction of stress. In addition are the concept of this method and separation of phases outlined.

The measurement of anisotropy of magnetic susceptibility is a suitable technique for quantifying the magnetic fabric of a pluton using cores with 25 mm diameter and 50 to 100 mm length. The origin of magnetic fabrics in granites is mainly described in terms of orientation of crystals, which occurred during defonnation of cooling magma before its complete crystallisation.In this paper, principles of anisotropy of magnetic susceptibility (AMS) and its applications in determination of magnetic fabrics of Shah-Kuh is presented. The magnitude of magnetic susceptibility in different units of this pluton ranges between 79 to 2896µ SI. These values, as well as Fe-content in different specimens, indicate that minerals responsible for anisotropy of magnetic susceptibility are mainly magnetite, hornblende and biotite, in lesser significance. Accordingly, Shah-Kuh granite, except its greisenic granite and leucocratic microgranite, could be classified as ferromagnetic granite. This conclusion confirms the earlier petrological studies, which classified Shah-Kuh granite as an I- type granites. The presence of tourmaline in the greisenic granite and leucocratic microgranite results in an inverse magnetic fabric. Such rocks, due to their inverse magnetic fabric, need more detail AMS study. Nearly vertical magnetic foliation, observed in the some specimens, probably represents their primary location in the wall of pluton. Specimens with vertical magnetic lineations, from granodiorites adjacent to of Deh- Margh village, may be evidence of magma feeder zone.

A 2D inversion of magnetotelluric data was carried out from geothermal resources at Mount Sabalan in the north west of Iran. The algorithms used in the MT study are the 2D models of Occam's inversion. Profile A with 13 MT stations was passed through Gheynarge village and aligned NW-SE around the west flank of the volcanic mountains of Sabalan. 2D inversion of magnetotelluric indicates a zone of very low resistively nearby Gheynarge springs. The geothermal model was considered with a 100 ohm-m cap overlaying a 5 ohm-m reservoir in a 400 ohm-m half-space. The response of the regarded model confirms the 2D Occam's inversion obtained from MT data in the west of Mount Sabalan. The Combination of 2D inversion from three profiles, which crossed on the A profile, indicates a 2.5D interpretation of Meshkin-Shahr's geothermal site's reservoir.

Measurement of liberation degree is of prime importance in determination of grinding and separation circuits' performance.Subsampling and particles mounting, which are the main stages in the preparation of polished sections, could affect liberation degrees obtained by the mineral counting method.At the Sarcheshmeh copper mine, particles mounting are carried out at high pressure (4000 psi) and high temperature (300°F). In this paper, the method of percent weight determination of copper- bearing minerals (chalcopyrite, chalcocite and covellite) and the error on liberation degree estimation are discussed. In order to determine the appropriate weight ratio of sample to mounting powder, 10 samples with five different weight ratios were examined. It was found that the weight ratio of 4g sample to 11 g mounting powder had the lowest error. For each mineral, the minimum numbers of particles, which must be examined to reach an acceptable accuracy were determined.

Besides some limited information available in the literature, the record of Mesozoic vertebrates, specially dinosaur faunas, in the Middle East are scarce.Among the countries of this region, Iran has the greatest potential for new findings, since extensive areas with Mesozoic continental deposits, particularly around Kerman and east of Central Iran are reported. An Iranian-Brazilian expedition, with the support of the Geological Survey of Iran, was scheduled in September 2002. in northern parts of Kerman area in order to investigate the potential for finding Mesozoic terrestrial fossils. In this survey the lower Jurassic dinosaur footprints of the Neyzar Valley was restudied. Reinterpretation of these footprints which are found in two different horizons indicates that they were made rather by theropod than ornithopod dinosaurs.Prospecting in the Late Jurassic / Early Cretaceous red beds of the Ab Bid syncline, western flank of Kuh - e - Takhtgah, north of Kerman, yielded the first dinosaur skeletal remains, including a complete theropod dinosaur tooth crown and some bone fragments.

More than 80% of drinking water of highly populated and expanding city of Gorgan, as one of agricultural centers of Iran, is supplied by local groundwater resources (Ziarat, Garmabdasht, and Shast-kola aquifers). Chemical analysis of groundwater samples of Gorgan district indicates two regions of anomalously high concentration of nitrate (Ziarat aquifer) in the urban area. High chloride concentration in water from dug wells corresponds with the anomalous high values of nitrate. Low concentration of nitrate in Shast-kola as well as Garmabdasht aquifers, where main land use is agricultural activities respect to Ziarat aquifer, demonstrates low/no effects of fertilizers on the contamination of groundwater. Determination of No3/Cl and K/Cl ratios depicts sewage effluents and urban runoff as the main sources of nitrate contamination of the groundwater. Moreover, rapid urbanization and the encroachment of residential development into surrounding forests release considerable nitrate to the underlying shallow aquifers.

The study area is located in southeast of the fold-thrust belt of Zagros. The belt is influenced by sub- surface structures and the creation of young deformations during the late Alpine Orogeny. Remotely sensed data showed that the area suffered structural complications due to the influence of the superimposition of deformation resulted from the younger transverse lineaments over the foreland fold-thrust structures. Two systems of sub-surface transversed faults have been identifie, using the visual interpretation of satellite images, review of the evidences such as curvilinear hinge geometry of the folds and the existance of similar deformations in the sub-surface structures, formatin of different folded trends, axial interaction of the folds, generation of brachyanticlines, and alignment of the upper proterozoic salt plugs.The first system has an identified trending 0 to 90 on the basis of their left-lateral displacement of the fold-thrust structures and trend of the salt plugs.While the second system, trending 270 to 360 has a lower capability in diapirism and outcrop of the salt plugs; therefore, a weak alignment of salt plugs is observed in their trend. On the basis of the curvilinear folded geometry in the foreland part of the orogen, right-lateral displacement was analyzed for this system. while Statistical analysis of the structural lineaments extracted from the satellite images shows that the principal stress axis, trending 20, is more dominant in the area. The performance of this stress resulted in two systems of conjugate shear faults with dominant strike-slip component. The left - lateral strike-slip component is observed in the sub-surface faults trending 0 to 90. The right-lateral strike-slip component is visible in the sub-surface faults trending 270 to 360. With respect to various similarities in statistical hystograms of the structural lineaments of southeast and northwest of Zagros, the suggested structural pattern in the area under study, could probably be applicable for all of the Zagros.Furtheremore, the suggested structural pattern could assist to verify and explain some of considered probable reasons for the inconsistant distribution of the salt domes in the area.The northern part of Iraq and southeast of Zagros, the north and northeast margins of the Arabian plateau, have many similarities with the basement tectonic pattern of the northeast Arabic plate in Saudi Arabia. The similar trend of most conjugate shear faults and also the brachyanticlines (in the area of study) with the strike of the basement faults and their over/aping young folds in the northeast of the Arabic plate in Saudi Arabia indicate that these faults are deep-seated and therefore of basement type.

The shale unit of the Lalun Formation in Tuyeh-Darvar area (Southwest of Damghan) is unconformably underlain by the sandstone unit and is gradationally overlain by Top Quartzite unit of the Lalun Formation. The shale unit of the Lalun Formation is composed of siliciclastic facies and two carbonate horizons (less than two meters thick) in the lower part of the shale unit. These carbonate horizons include dolomitized rnicrobialite and ooide grainstone facies, which were deposited in a estuary environment of the northwestern passive margin of Gondwana, following late Early Cambrian mass extinction.

The basement of Kopet-Dagh basin is formed of pre-Jurassic rock units. The exposed units in Aghdarband area were strongly deformed during Hercynian, Cimmerian and Alpian orogenies. Hercynian orogeny generated metamorphism of green schist facies with strong faulting, whereas Cimmerian orogeny caused Triassic thrust faulting. Alpine orogeny (Paleogene to Recent) causesd the folding of sediments of the Kopet-Dagh basin and had formed initially thrust faults and then, oblique slip faults (strike slip with reverse movement) in the region. These faults are still active.Rock units in the basement contain sedimentary and igneous rocks. The sedimentary rocks are composed mainly of volcanogenic siliciclastic sediments, including conglomerate, sandstone and shale (Devonian to Triassic age).The small outcrops of igneous rocks are exposed in the southwest of the Aghdarband area and include two rock units: 1-Darreh Anjir ophiolith complex that contains gabbro and ultramafic rocks.2- Acid tuffsThese rocks were mixed with ophiolithic rocks by thrust faults and appeared in the form of thin nappes.

Diatomites of Azarbayjan region are siliceous sediment formed by depositeion of diatom frustules.In this research we focused on systematics of diatomes and uesd polarizing and scanning electron microscope (SEM) to study the samples.Finally 17 genus and 33 species of diatoms were recognized and systematic determination of them presented. We found that the population of Centrales was less than that of Pennales and the age of the deposits determined as Late Pliocene to Pleiostocene. Study of nannofacies of diatomites made it clear that the samples of Mameghan region have better quality and Samples of Maragheh need more processing. Systematic study of diatoms morphology by ultra microscope, internal structure, size and percentage abundance helped us to determine nannoporosity and the degree of Purity to use for multiple purposes such as filteration, medical, health, chemistry industries and etc..

Recently radar images have a large ability in different geological applications compared with the optical images. These applications are based on lineament and fault extraction, DEM generation and displacement determination. But radar images are introduced to a kind of speckle noise called speckle noise, which decreases the image quality and interpretability.Therefore, radiometric correction is an important step to increase the quality of radar images before using them.In this paper, an improved speckle noise reduction method is presented based on wavelet transform. A 2D Gaussian function is found to be the best model fitted to the speckle noise pattern cross-section in the logarithmically transformed noisy image. Therefore, a Gaussian low pass filter using a trous algorithm has been used to decompose the image. A Bayesian estimator is applied to the wavelet coefficients of the logarithmically transformed image to estimate the best value for the noise-free signal.This estimation is based on alpha-stable and Gaussian distribution hypotheses for wavelet coefficients of the signal and noise, respectively. Quantitative and qualitative comparisons of the results obtained by the new method with the results achieved from the other speckle noise reduction techniques demonstrate its higher performance for speckle reduction in SAR images.

Gravity and its usage in gravity interpretation is still a challenging field. It is not easy to compute these gradients especially in the case of noisy data. Analytical signal is one of the new methods that uses gravity gradients to locate the perturbing body. This method had already been used for high-resolution magnetic and gravity data and rarely used for low-quality gravity data. The gravity gradients and analytical signal have been applied in two different areas, Zahedan where we are looking for Choromite anomalies and Tehran (Mard Abad) where we are investigating for low density anomaly, Probably hydrocarbon.