فصلنامه زمین شناسی ایران
پیاپی 35 (پاییز 1394)

Inversion of the gravity data is one of the most interesting numerical tools for obtaining three dimensional geological images. In this paper 3D nonlinear inversion of the gravity data is used to determine the basement topography. The basement was juxtaposed with the regular array of rectangular prisms in which the thickness of each prism is determined by the inversion procedures. Prepared algorithm is based on singular value decomposition (SVD) method which ca modify the initial model by comparing observed and estimated gravity data. The SVD method is very popular with geophysical data analysts because it is mathematically robust and numerically stable. To illustrate effectiveness of the prepared codes and algorithm related to 3D inversion of gravity data, both synthetic and real data were tested by the mentioned algorithm. The real data were part of the gravity data which were acquired in Moghan area (located in the north-west of Iran). Because of being near to the Baku oil-rich regions and thick sedimentary rocks, the Moghan sedimentary basin is an interesting area from hydrocarbon exploration point of view. Determination of the sedimentary rocks thickness is an important factor in oil and gas exploration issues. The main goal of 3D inversion of the gravity data in the study area is to determine basement the sedimentary rocks thicknesses or the boundary of Ojagh-Gheslagh Formation and its volcanic basement. The modeled boundary of Ojagh-Gheshlagh Formation and its volcanic basement which is obtained by the inversion of gravity data, was previously confirmed by interpretation of seismic data.

In this study, the optimized DRASTIC model parameters and land use layer (LU) were used to assess specific vulnerability in Kashan aquifer using statistical methods. Information layers were prepared, rated (deterministic and fuzzy-statistical), weighted (original and statistical) and combined (by Index-Overlay method) in GIS environment. For optimization of DRASTIC model, nonlinear regression for fuzzy-statistical rating (scaling) and Pearson correlation coefficients between nitrate concentrations and scaling parameters of DRASTIC model and sensitivity analysis (removal and single-parameter) were performed to determine and modify weighted parameters. As a result, RASIC-LU model with statistical rating and weighting, single-parameter sensitivity analysis, determined the best selection model based on correlation coefficient = 61.1%, P-Value= 0.001 and with parameters of net recharge, aquifer media, soil media, impact of vadose zone, hydraulic conductivity and land use with weight values of 2.50, 4.63, 4.15, 3.03, 1.96 and 2.00 respectively. According to this model, western and southern parts of the aquifer has a high and very high pollution risk due to high net recharge, pollutant land use and coarse-grain material in the impact of vadose zone, soil and aquifer media. In addition, sensitivity analysis based on mean squares error (MSE) indicated that this model is more sensitive to removal and increase of parameters weight of land use, soil media, impact of vadose zone, aquifer media, net recharge and hydraulic conductivity, and shows a decreasing ternd, respectivily.

The study area is located in the Northwest of Iran and North of Khoy Ophiolite Belt. Rocks of the Ghareh-Aghaj region include Qum formation, Upper Red Formation and Pliocene conglomerate. Pliocene rock units consist of siltstone, sandstone (arkose and lithic arenite) and microconglomerate- conglomerate. Pliocene cicroconglomerate- conglomerate hosted strata bound copper mineralization in the Ghareh Aghaj region, but the mineralization is partially seen in the sandstone unit. Much of the mineralization in the study area is open space filling and disseminated. Ore mineralogy of Ghareh-Aghaj is very simple and contains of native copper, cuprite and tenorite. Lack of copper sulfides, the absence of plant fossils as reducing agent, and the non-occurrence of copper replacement instead of plant tissues, occurance of mineralization as the open space filling and cement grain and formation of native copper as the main ore, all represent the dissimilarity of Ghareh-Aghaj Cu mineralization with Redbed type sedimentary copper deposits. Formation of Ghareh-Aghaj copper deposit can be explained as follows: Pore water formation of diagenetic processes within the Upper Red Formation caused the leaching of copper from this sequence and the formation of copper chloride complexes. Increasing of water table caused the development of reducing conditions in the Pliocene conglomerate. Therefore entrance of Copper-bearing fluids caused native copper deposition below the water table. Decreasing of groundwater table and exposure of native copper to the oxidizing conditions caused the replacement of cuprite, malachite and azurite with native copper.

This study uses multiple inversion method to analyze slip data on shear planes and faults containing slickenlines in different rock units, and evaluates paleostress field in Mansour-Abad area. It was gathered the required kinematic data in 18 stations according to the stratigraphic age of the rock units. It was used the most important shear sense indicators, including mineral steps, Riedel shears and tension fractures. According to the multiple inversion method, which calculates stress tensor from the inhomogeneous fault data (data without any knowledge of stress field orientation or fault classification), four parameters of stress ellipsoid shape and axes were analyzed. It was found 3 different phases of compression, extension-shear and shear- compression using the phase separation in this method. The maximum principal stress orientation in different locations changes from N24˚ to N162˚ between Cretaceous and Neogene, while the minimum principal stress orientation changes from N79˚ to N116˚. The NW-SE strike of the reverse faults indicates that these faults developed during the activity of compressional phase. During the extensional-shear phase of the activity, local sedimentation occurred in the area. Late shear deformation of area, and change in stress field orientation, resulted in a block rotation between the fractures. Further increase in the rotation caused the fractures to increase in size, and provide space for intrusion of the magma.

Understanding the interactions of ground water and surface water is one of the most important challenges among hydrogeologists. Hydraulic gradient between ground water and surface water, as well as hydraulic conductivity of streambed sediments are required to determine ground water and surface water exchanges. Minipiezometers are simple instruments that measure flow direction and hydraulic gradients between ground water and surface water. Often temporarily installed, minipiezometers are essentially small-scaled versions of piezometers, which are commonly used to make groundwater level measurements. By combining water table data with surface water level measurements, flow direction can be determined. Minipiezometers are typically used in the areas where many measurements are required. Commercial minipiezometers are available, but they are very expensive. The purpose of this paper is to design and construc a low-cost minipiezometer for measuring ground water and surface water exchanges. In this study, a minipiezometer was made by simple and available materials such as steel pipe, steel 3NPSoft rob, clear plastic hose, gas valves, hand vacuum pump, hammer, U-shape clear tubing, graduated manometer board, and graduated transparent plastic cylinder and was successfully tested in the Soleghan River in the west of Tehran.

Sulfur source tracing based on of sulfide (galena and pyrite) and sulfate (barite) mineralization in fluorite deposits of Elika Formation (East of Mazandaran Province) is studied. In present research. δ34S values vary between -1.82 – +12.49 ‰, +13.22 – +25.83 ‰ and +22.69 – +32.91 ‰ for galena, pyrite and barite, respectively. Regionally, although wide range of δ34S in sulfides is interpreted as isotopic heterogeneity of source and/or processes of reduced sulfur supply for sulfide mineralization in the studied area, but each deposit has narrow range of δ34S. Compared to sulfides, barites show isotopic homogeneity in heavier δ34S which are corresponding to evaporates from coexisted sea water (Middle-Upper Triassic; Paland Formation). Based on stratigraphic and mineralogical data of host rocks, co-existing evaporates of Triassic sea water and also diagenetic primary sulfates in matrix of host rocks (anhydrite, gypsum, barite) are introduced as the most probable sources of sulfur for sulfide mineralization in Shesh Rodbar and Era deposits. In contrast, contribution of organic matter and/or diagenetic primary pyrites had main role in generation of light δ34S values in Pachi Miana and Kamarposht deposits. Thermo-chemical reduction of digenetic primary sulfates and thermal decomposition of diagenetic primary sulfides as well as sulfur bonds in organic matter-bearing laminaes in the host rock are introduced as main processes for reduced sulfur supply in sulfide mineralization.

Late Cimmerian tectonic phase was the main cause for depositing terrigenous-evaporite sediments of the Shurijeh Formation in large area of eastern and central part of Kopet Dagh Basin during Late Jurassic-Early Cretaceous. In order to recognize facies changes and depositional environments of the Shurijeh Formation in east of the Kopet Dagh, 3 stratigraphic sections including Baghak and Mozduran surface sections and a well from Khangiran gas field were selected and studied. Field surveys together with microscopic studies of 311 thin sections reveal that depositional environment of the lower part of the Shurijeh Formation is mainly interpreted as fluvial environment, especially braided and meandering rivers. In the upper part of this formation, coastal plain and tidal flat facies, which locally contain lagoon and shoal sediments, are observed.

Tang-e-Hana region is located in the Snandaj-Sirjan structural zone in the Northwestern of Neyriz in the East of Fars province. The area mainly consists of ultramafic (harzburgite, dunite, wherlite), mafic (gabbro) and marble rocks which are partly metamorphosed to skarn. Contact of ultramafic rocks and Cretaceous limestone unites caused formation of marble and skarn rocks in the study area. The main minerals in skarns are garnet (andradite, grossular), clinopyroxene (diopside, hedenbergite), vesuvianite, scapolite, wollastonite and magnetite. The skarn rocks show different spatial distribution, so that the formation of wollastonite increases and garnet formation decreases from SE to NW of the study area. The existence of wollastonite in the skarns of northern part of Tang-e-Hana is due to high temperature gradient and. According to microprobe analysis and field studies the temperature of the skarn rocks at the time of generation was estimated between 400°-600°C. Also the effective pressure of oxygen was changed between 10-15 to 10-2 atmosphere.