GEOSCIENCES
Year:2009 | Volume:18 | Issue:70|Papers Count:22

A considerable portion of potable water in Iran is supplied by natural glaciers, and then the study and protection of these resources are a necessity. This investigation includes the assessment of glacier parameters such as maximum and minimum altitude, area and perimeter, position of snow line and etc. Since direct measurement of these parameters in the field is time consuming and expensive, therefore, some techniques such as remote sensing seem to be more useful and plausible.  In this regards, one can deploy different algorithms for detection of the glacier region as well as calculation of relevant important parameters.To achieve this goal, the resolution of satellite images in spatial, spectral and radiometric aspects should be studied and assessed.  In this research, satellite images with different resolutions have been used to study the Alam Chal Glacier. Using different satellite images, the glacier parameters have been identified and studied and the most appropriate images which can provide the necessary precision for this task were identified.Also the potentiality of DEM (Digital Elevation Model) in combination with satellite images in order to obtain the glacier geometric elements such as the topography of cirque, maximum and minimum height, the topography of the district and watershed, has been investigated.

Soltan anticline is located in northwest of the Zagros fold-thrust belt in the Lorestan Province. Geometric and kinematic analyses of the anticline have been carried out to estimate the closure of the Dehram Group in order to evaluate its potential for gas reservoirs. Geometric analyses of the Soltan anticline indicate that the fold geometry is rather similar to that of the Trishear type of fault propagation folds. However, considering the competency contrasts between various rock units in the anticline that control the fold’s geometry, together with the rounded and relatively wide outline of the anticline at surface, the Soltan anticline can also be compared to faulted detachment folds that hold the same geometry as the fault propagation folds. On the other hand, the very low values of finite strain measured on clastic rocks collected from the anticline and its typical smaller scale fold constraint, and the low values of the layer parallel shortening are comparable to the kinematics of fault propagation folds. Based on the data from the geometric and kinematic analyses, seven structural cross sections across the anticline are drawn, and using the cross sections, a structural contour map and a 3D model for Dehram Group are constructed. The calculated values for the anticline closure prohibits this structure as an appropriate host to gas reservoirs, unless the Soltan anticline is connected to the adjacent, Rit, anticline.

To study the Shirgesht Formation biostratigraphy in Kalmard Horst in relation to its conodont content, the Miyugodar (Miangodar) stratigraphic section was selected which is located in southwest of Tabas city. The Shirgesht Formation in the mentioned section is mainly composed of siliciclastic rock units and overlay unconformably on Kalmard Formation (attributed to Pre-Cambrian) and is overlain by Gachal Formation (Carboniferous). Thirty five rock samples were selected from appropriate rock units (Shirgesht and Gachal Formation). Samples were studied in laboratory for more details. According to the extracted conodont from Shirgesht Formation in Miyugodar section, the age of this formation can be regarded as Early Ordovician (Tremadocian – Arenigian). Three conodont assemblage zones were recognized in Early Ordovician units. They are: Cordylodus spp., Deltifer and Proteus Global Standard Conodont biozones. The recognized biozones are as followe: 1- Oneotodus - Drepanodus Assemblage Zone2- Acodus deltatus - Protopanderodus Assemblage Zone3- Acodus - Oistodus Assemblage Zone

Study of source rock materials in Jajarm bauxite deposit is the main subject of this study to show its origin. From bottom to top, this deposit consists of lower argillaceous layer, argillaceous bauxite, hard bauxite and upper kaolinite units. Correlation coefficients and scatter diagrams of immobile elements in these four layers, demonstrate an early homogenous origin at the beginning of the bauxite formation. Accordingly, source materials were separated slowly due to the different conditions dominated in different parts of the deposit. Difference in drainage conditions and leaching of some elements from upper part and their re-deposition in lower parts of the deposit are the main reasons for hard bauxite separation from argillaceous one. Formation of the lower argillaceous layer, located between argillaceous bauxite and carbonate footwall is due to the direct contact of the argillaceous bauxite and carbonate footwall and also difference in drainage rate in contact area of the two layers. Geochemical evidence also depicts that upper kaolinite formation is the result of the silica leaching from upper horizons and its re-deposition in hard bauxites. Compositional comparison of studied samples with chondrite and upper continental crust demonstrates the effect of both of the basic and sedimentary rocks in evolution of the Jajarm bauxite. Formation of this deposit can be considered as a result of the alteration of the primitive laterite in an area close to the current location of the deposit. During alteration and transportation bauxite is deposited on the karstic topography and then some continental sediment was added to it.

The Plio-Quaternary calc-alkaline magmatism in Azerbaijan, northwest Iran, occurs as stratovolcanoes, lava flows and domes consisting of andesitic basalts, andesites, dacites, rhyodacites, and pyroclastic materials. The volcanic rocks unconformably cover the Miocene sedimentary formations. The chemistry of the felsic-intermediate volcanic rocks indicates that the parent magmas are medium-K calc-alkaline and metaluminous in nature, and are distinguished by Na2O/K2O> 1. The volcanic rocks are enriched in LILE and LREE, and depleted in Y, Nb, and HREE, and display highly fractionated REE patterns, with no Eu anomaly. They display post-collision and continental margin arcs affinities. The post collision convergence between Arabia and Eurasia continental plates, starting in Miocene, resulted in significant shortening, thickening, and uplift of the crust in northwestern Iran and eastern Turkey, and shaped the present Iran-Turkey Plateau.The thermal perturbation processes in the underlying asthenospheric mantle led to partial melting at a low degree, producing alkali- basalt magmas, with garnet remaining stable in the source region. The ascent of the basaltic magma and its emplacement in the lower crust resulted in the partial melting of the crustal materials and development of acidic magma. These processes led to the ascent and eruption of the felsic magmas prior to the mafic magmas. Mixing of mantle-derived mafic magmas with felsic magmas of crustal origin, produced hybrid magmas of intermediate composition. The occurrence of inverted volcanic sequences, where olivine-alkaline basalts are underlain by calc-alkaline felsic-intermediate rocks, are typical features of bimodal volcanic activities in the Plio-Quaternary times in Azerbaijan.There are mineralogical as well as geochemical evidences that AFC-type processes were involved in the evolution of the Plio-Quaternary volcanic rocks in Azerbaijan. A comparison of geological and geochemical characteristics of the Plio-Quaternary volcanic rocks from northwest Iran with those from eastern Turkey indicates that the two areas share similar evolution paths in the petrogenesis of magmatic rocks.

Today, one of the main objectives of the geodesy is to identify the changes over time at the surface of the earth. It is critical to the design of the infrastructures to know these changes and to be able to predict their trends with time, as any ignorance could lead to in compensable losses to the society. One way to investigate and measure the changes is to establish permanent GPS stations and to process the time series data from the stations. The amplitude and mode of the periodic movements and the parameters of the linear movements can be investigated by the application of the maximum likelihood of the type and amplitude of the noises in the time series.The noise analysis in time series allows the real changes recorded in any stations in the geodynamic network to be accurately measured. With the application of the measured parameters in the deformation equations, the changes in the crust of the earth can be appropriately interpreted. This research shows that the white and flicker noises in vertical components are more than those in the horizontal components. Without the application of noise analysis on time series, the estimated errors for the rate of changes in the geodynamic stations would be underestimated by 8 times.

The Astaneh fault with a length of more than 75 km is located in NW of Damghan. Morphotectonic investigation along the Astaneh fault and left - lateral displacement in quaternary deposits shows that, Astaneh is an active fault. It is necessary to recognize paleoseismicity of Astaneh fault because, this fault is located in seismic zone of Komes historical earthquake with Ms=7.9 (Ambraseys & Melville, 1982). Many people (more than 45000) were killed in Damghan city in Komes historical earthquake. In this paper, 4-5 paleo events along the Astaneh fault are presented through paleoseismological investigation.

In general, seismic attenuation is caused by a combination of both scattering and intrinsic mechanisms. Scattering redistributes wave energy within the medium but does not remove energy from the overall wave field. In contrast, intrinsic attenuation mechanisms convert wave energy to heat through friction, viscosity, and thermal relaxation processes. The frequency-domain spectral decay method is employed to estimate frequency dependence value of Qs.We used foreshock, main-shock and aftershock of Darb-e-Astane earthquake acceleration data with magnitude of 5.1, 6.1 and 4.9 for estimation at 1.5, 3, 6, 12 and 24 Hz central frequencies, respectively. The estimated average frequency dependence shear wave quality factor gives the relation Qs= (109±6) ƒ (0.5±0.08). Shear wave quality factor are increasing from 156 to 592 at frequency band of 1-2 Hz and 16-32 Hz, respectively.The Q0 value with frequency for this area is similar to those obtained for similar tectonically active regions in the world.

One of the duties of seismic interpreter is interpretation of the geological structures likely to be found at deeper levels. Such constructions form a key to the understanding of regional tectonics and they often play a vital role in industry. The exploration for oil and gas in particular requires the best possible control on underground structures in order to locate drill holes for exploration investigation or for producing wells. Because the primary data are always incomplete and may be in part contradictory, the final interpretation should be at least geometrically validated. A powerful and independent test for the validity of a structural interpretation is the restoration of the structure to the shape it had before deformation. Restoration is a fundamental test of the consistency of the interpretation. It is best described by transformation equations which incorporate rigid translation and rotation plus deformation. A map or cross section can usually be restored by methods based on more than one kinematic model, and different methods will produce somewhat different restored geometries. It follows that any given restoration doesn’t necessarily represent the exact pre-deformation geometry. The internal consistency of the restoration by any technique constitutes a validation of the interpretation. In this study, the main aim is introducing the balancing of seismic interpretation and its application to decrease the errors of interpretation. For this purpose, length and area balancing were done at a sample seismic cross section from 3D seismic data of two oilfields at the East of Khuzestan (SW Iran). As a result, the primary interpretation was corrected and finally the corrected interpretation was compared with primary interpretation. For balancing of seismic sections in this area, the flexural slip technique is selected as optimum technique through testing line-length, vertical simple shear and flexural slip techniques.

ChahMoosa, Kalate ChahMoosa and GholeKaftaran mining districts are located in the Eastern part of Toroud-ChahShirin magmatic arc. Calc-alkaline subvolcanic bodies’ of ChahMoosa porphyry biotite hornblende andesite, GholeKaftaran porphyry biotite hornblende dacite, equivalent to I type granite, intruded Eocene volcanic-pyroclastic sequences. Disseminated-veinlet Cu mineralization in the ChahMoosa mine occurred in subvolcanic porphyry biotite hornblende andesite bodies are associated with phyllic and propylitic alterations. Supergene processes caused extensive alteration of hypogene sulfide minerals such as pyrite, chalcopyrite and bornite to secondary chalcocite, covellite, digenite, malachite and neotocite supergene minerals. Disseminated-veinlet Cu, Zn, Pb mineralization at Kalate ChahMoosa which is limited to a fault zone in porphyry biotite hornblende andesite subvolcanic body. This mineralization is accompanied by phyllic, propylitic, and silicic alterations and includes hypogene minerals such as pyrite, chalcopyrite, sphalerite, bornite, galena, barite and supergene minerals such as chalcocite, covellite, malachite and neotocite supergene minerals. In the abandoned Southern GholehKaftaran Cu mine, Cu bearing veins have occurred in porphyry biotite hornblende  dacite body and contain quartz, chalcocite, and malachite. In the abandoned northern GholehKaftaran Pb mine, Pb (Zn, Cu) bearing veins occurred in porphyry biotite hornblende dacite body and they contain galena, sphalerite, pyrite, chalcocite, calcite and barite. Fluid inclusion studies show that homogenization temperature decreases gradually from ChahMoosa toward Kalate ChahMoosa to northern GholehKaftaran. Based on petrography, structures, textures, mineral paragenesis, fluid inclusion and geochemical studies, it can be concluded that mineralization at ChahMoosa-GholeKaftaran district has characteristics of an individual mineralization system. This system is related to evolution of hydrothermal fluid mineralization and their mixing with cold and low salinity meteoric water resulted in disseminated-veinlet Cu mineralization at relatively deep zones, and vein type Cu, Zn, Pb at shallow zones has led to development of elemental and mineralogical zonations.

For interpretation of paragenetic sequence and post depositional history of siliciclastic sediments of Dahu Formation (Late Camberian), two stratigraphy sections were measured at Dahuieh (type section) and Gazuieh in the NE and E of Zarand, with the thickness of 240 and 227 meters, respectively. The diagenetic processes affected these sediments, during three stages eogenesis, mesogenesis and telogenesis, including compaction, cementation, alteration, dissolution, fracturing and vein filling. Clay mineral study within sandstone and mud rocks of Dahu Formation led to identification of two groups of clay as illite and cholerite. Illite form 90% of clay minerals in these sediments that are mostly formed during burials and clay mineral diagenesis as well as alteration and dissolution of potassium feldspar. The interpreted paragenetic sequence shows that a large number of diagenetic processes act in the mesogenetic stage. Physical compaction and hematite cement have operated in eogenetic stage, while other processes such as chemical compaction, silica and dolomite cement, feldspar alteration, sericitization, ilitization and chloritization, dissolution of feldspars and cherts have occurred in mesogenetic stage. The fractures and calcite vein filling have formed in telogenetic stage during uplifting. We hope that this information can be used for evaluation of post depositional and burial history of similar sediments in local and regional scale.

The North Tabriz Fault (NTF) is an active fault which poses a high seismic hazard to the areas of NW Iran, especially the city of Tabriz with a population of 1.6 million. In order to determine the geometry and the kinematics of this fault system, a local dense seismological network including forthy 3-component stations was installed around the central segment of Tabriz Fault which crosses the northern part of the city of Tabriz. This network operated for 3 months. Using microearthquakes recorded by our temporary network in addition of more than 6 years of local events recorded by 8 permanent stations of Tabriz telemetry network, the 1-D crustal velocity of the region was determined. Our results indicates that the upper crust consists of a ~6 km thick sedimentary layer (VP = 5.23 km s-1) overlying a ~18 km thick upper crystalline crust (VP = 5.85 km s-1). We estimate a velocity of 6.54 km s-1 for the lower crystalline crust, but the limited focal depths of our local events did not allow determining the thickness of this layer. The well-located earthquakes indicate the seismic activity along the Tabriz fault. Precise examination of the focal depths on different cross sections indicates that the western and central segment of this fault system dip northeast ward while the eastern part shows almost southwest dipping plane. Calculated focal mechanism all indicates the right-lateral strike-slip motion of the Tabriz Fault. The most reliable fault plane solutions are consistent with cross sections showing evidence of extension in Eastern part comparing to compression observed in Western segment. Our focal mechanisms and geodetic studies using GPS measurements indicate that the North Tabriz Fault helps to northeast motion of trapped crust in this area. 

Hired gold-bearing area is located to the northeast of the Lut zone and in the vicinity of the Sistan suture zone. Several post Eocene plutons have intruded into the Eocene volcanic and pyroclastic units and caused hydrothermal alteration and mineralization of gold, copper, lead and zinc. We have applied the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data including three visible and near infrared (VNIR), six shortwave infrared (SWIR) and five thermal infrared (TIR) bands to determine the alteration minerals of Hired gold-bearing area. Spectral analysis of the surface reflectance SWIR manifests absorption in 2.20 mm and 2.33mm wavelength regions. Absorption at 2.20mm (band6), due to Al-OH anionic agent is consistent with the presence of clay minerals (illite, kaolinite) and sericite, whereas absorption at 2.33mm (band 8) due to Mg-OH anionic agent and carbonates is consistent with the occurrence of chlorite, epidote and calcite minerals.In this study different image processing techniques such as band combination, band ratios transformation, and Binary Encoding were used to identify and delineate the altered minerals accompanied by gold mineralization. The Binary Encoding method was found to be the best image processing technique for delineation of the hydrothermally formed minerals.Analysis of the spectral emission data in the five TIR bands has provided valuable lithological information. It would not be possible to identify silicified rocks in the nine VNIR+SWIR bands due to the lack of recognizable spectral absorption features in quartz at this wavelength region. We have therefore mapped Quartz-bearing surface deposits as well as hydrothermally silicified rocks in the TIR region by using a band ratio (b11×b11) / (b10×b12) image. The results obtained from ASTER data are compatible with conclusions inferred from petrographic and XRD studies of the surface samples. The ASTER data appear to be useful in mapping hydrothermal alteration and in ore deposit exploration.

Two bryozoan species are described from the Geirud Formation (Upper Devonian) of Central Alborz. The Geirud Formation is a sequence of nearly 340 meters of alternating silisiclastics and limestone and 1-2 andesitic lava units, with extensive exposures in the Central Alborz Mountains. The study comprises the Type Section of the Geirud Formation in the Geirud valley and two sections in Zaigun and Lalun valleys near the Type Section, all in northern Tehran (Fig.1).  In some calcareous beds we  found bryozoan species from Famennian.  Trepostome Schulgina mutabilis TROIZKAYA, 1975 is known from the Upper Devonian (Famennian) of Central Kazakhstan. The Ascopora .sp. is the earliest known representative of habdomesine genus Ascopora TRAUTSCHOLD, 1876. This is the first study on the bryozoans of the Geirud Formation in Central Alborz.

Arghash gold district includes five gold-bearing vein systems, (Au-I to Au-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-I to Py-IV). Py-I to III are intimately associated with gold; however, Py-IV is barren. The d34S values of pyrites in conventional bulk analyses fall into two groups, one highly enriched in 34S (d34S= +9.3 to +21.8‰), and the other less enriched to slightly depleted in 34S (d34S= +5.1 to -4.3‰). In-situ laser probe experiments were carried out to characterize various generations of pyrite. The results indicate a relatively narrow range for Py-I to Py-III (d34S= -5.8 to +0.1‰) consistent with a magmatic source for sulfur. Py-IV is highly enriched (d34S= +8.9 to +23.7‰), implying contributions of sulfur from sources enriched in 34S, like evaporites. The high d34S values in the enriched group can be attributed to a significant occurrence of Py-IV in this group.The d34S values of two stibnites from Sb ore (-18.8 and -14.4‰) suggest a different sulfur, and possibly metal source, and/or radical changes in the physicochemical conditions of the fluid during deposition of stibnite. Metasedimentary basement rocks could contribute sulfur and metal to the circulating fluids. d13CPDB values of vein calcites are near 1 per mil suggesting a sedimentary source for carbon. Carbonate units and interlayer’s in the area are a suitable source for CO2 in the ore fluids. The stable isotope data suggest that hydrothermal fluids experienced a complex history of water/rock interaction and those ore components, were derived, at least partly, from country rocks.