فصلنامه زمین شناسی ایران
پیاپی 45 (بهار 1397)

Burkh anticline with the WNW-ESE trending is located in southeastern part of the Zagros fold-and-thrust belt and 40 km to the north of Bastak in the Fars zone. In this paper, based on the field data, satellite images and construction of the seven structural cross sections, structural geometry of the Burkh anticline is presented. Presence of the Precambrian- Cambrian of the Hormoz salt Formation as a basic detachment layer decouple the folded sedimentary cover from basement. Structural data show that the Burkh anticline is a detachment, buckle, asymmetrical and disharmonic fold. For describing tightness geometry of the fold, the term “open” is suggested. Field study and structural cross sections show that the Dashtak Formation as a middle detachment layer is the controlling factor for development of small-scale folding. Based on top of the Dehram Group underground contour map, vertical closure about 1000 m and horizontal closure of 200 km2 were calculated.

The Varandan Ba-Pb-Cu deposit is located in southwest of Qamsar which is part of Urumieh-Dokhtar magmatic-arc zone. Mineralozation occurred as four sub-horizons in the unit1 of volcaniclastics and volcanics (acidic tuff and andesite) of Middle-Late Eocene. Each sub-horizon consists of five ore facies including: 1) stringer zone, 2) vent complex zone, 3) massive zone, 4) bedded-banded zone and 5) hydrothermal-exhalative sediments of Fe and Mn bearing. Main wall rock alterations in the deposits include chloritic-quartz and quartz-sericitic. Alteration zoning is observed in the deposit as chloritic-quartz at the core and quartz-serisitic in the margins of the footwall of the ore sub-horizon. Electron microprob analysis (EPMA) on the chlorite in stringer zones of the second and third sub-horizons show that these chlorites are Fe-rich chlorite and close to the clinochlor field. Geochemical studies indicate that grades of Ag, As, Cu, Sb and Sr in the stratiform ore (bedded-banded and massive) of the third sub-horizon are much higher than the other sub-horizons, and are 41, 273, 1945, 390 and 1013 ppm, respectively. All geochemical studies show that metal zoning in this deposit is clear, this is characteristic of VMS deposits. Development of zone-refining and over refining processes caused leaching of Cu from the stringer zone and vent complex facies and its later precipitation in the bedded ore facies. Among across to different sub-horizons in the Varandan deposit, third sub-horizon is recognized as economic for Ag extraction .

High local groundwater flow into rock tunnels is a technical and environmental problem for underground constructions. Geological structures such as faults, open fractures, and dissolution channels could play important roles in conducting ground waters to the tunnels. However, prediction of groundwater inflow from these structures using analytical and empirical method often failed due to given hydrogeological assumptions and simplification such as a homogeneous and isotropic porous medium around the tunnel. The Zagros water tunnel is located in the northwest of Kermanshah province. A huge amount of groundwater flow into the tunnel through fractures occurred during drilling of the second part of tunnel. The second part of tunnel passes through Pabdeh and Gurpi formations. A considerable amount of groundwater flushed into the tunnel when the Ilam Formation was penetrated, causing numerous problems and great damage to the drilling operation. The goal of this study is to identify the factors that influenced water flows into the tunnel. To this purpose, geological features of high flow rate zones have been identified and investigated. The highest input rate (800 l/s) was recorded in the zone Hz23 located in Kurdighaseman anticline. The relationship between geological features and the groundwater inflow into the tunnel indicated that faults play conveying role for ground water into the tunnel. Evaluation of high local groundwater inflow to rock tunnels based on characterization of geological structures is more reliable compared to available analytical and empirical estimation.

Stream bank erosion is known to be a major source of sediment shedding in streams and rivers. However it is difficult to define and estimate the contribution of sediment from river erosion. The purpose of this paper is to demonstrate the application of BSTEM model as a viable tool for identifying and quantifying the controlling bank-slope conditions for a range of stream-restoration objectives, evaluation of the importance of fluvial erosion, vegetation properties and near-bank pore-water pressure properties. The Bank Stability and Toe Erosion Model (BSTEM) were used in order to predict streambank retreat due to both fluvial erosion and geotechnical failure. In this research, BSTEM model also was used to simulate hydraulic erosion at the bank toe and bank stability during a series of flow events (bankfull discharge, mean annual flood, maximum flood discharge) for the purpose of evaluating current (existing) and potential changes in failure frequency (factor of safety or FS) and stream bank-derived loadings. The study site is located at the exit point of the Lavij river from the mountains in Kashpal park area (Chamestan-noor). Every year there is a significant amount of bank erosion caused by large floods in this river section. This study showed that for a multilayered stream bank in Lavij River, the most significant retreat occurred during a series of high flow events. In fact, the floods that occur with a return period of more than 10 years, play an important role in fluvial erosion and lateral retreat processes. Results of BSTEM analysis showed that lateral retreat measured at the stream bank in different scenarios ranged from 0 to 81cm and the bank stability conditions in the first scenario is unstable (FS =0.9), but in the second and thirds scenarios is almost stable (FS=1.15-1.26). Bank top vegetation provided additional cohesive strength to the top 1.0 m of the bank and resulted in a further reduction of failure frequency and failure volume. Results of this study showed that toe protection added to eroding stream banks can reduce overall volumes of eroded sediment.

Golestan province is located in one of the seismically active zones of Iran. The seismicity maps of Golestan province show that density of earthquakes in the west is more than the east. In this research, the parameters including b-value, recurrence time and seismic moment were studied to investigate the seismicity of the west of Golestan province. The focal mechanism of earthuqakes and field data were used to determine the stress orientations in the study area. The estimated b-value is obtained as 1.24±0.2 which is comparable with the Alborz. Since the northern and southern parts of the study area have different geomorphological and structural characteristics, some of these parameters were calculated for two subdivisions; Dasht-e-Gorgan in the north and foothill in the south. Results of this study show that the earthquakes in the Dasht-e-Gorgan compared to the foothill are smaller with shorter recurrence times. For the foothills, the calculated P-axes using the stress tensor inversion method is found to be subhorizontal with trend N-NNE. For this region, at least two trends, N and NW, is calculated using field data. This result show the change of stress directions during the structural evolution of this area. The calculated p-axes trend for the Dasht-e-Gorgan is NE. In both studied areas, the focal mechanisms of greater earthquakes are consistent with the E-W to NE-SW trend of main faults especially the Khazar fault. But, the smaller events in the Gorgan Plain show a different trend and mechanism. Comparison of these two subdivisions shows that the northern Alborz foothill is more dangerous than the plain.

Geomorphic indices are major tools to recognize tectonics activities.
These indices have the advantage of being calculated from Arc GIS package over large areas as reconnaissance tool to identify possible geomorphic anomalies related to active tectonics.
In this research, Karkheh river basin was selected and six geomorphologic indices; drainage basin asymmetry (Af), stream-gradient index (SL), drainage basin shape index (Bs), mountain-front sinuosity index (Smf), valley floor width-height ratio (Vf) and hypsometric integral (Himatter) were calculated. Then, the values were classified in three groups and analyzed. The area of the three class as follows:Class2) 12180 km2, 23.7%
Class3) 32318km2, 62.9%
Class4) 6843km2, 13.3%
The region has an area of about 51341 km2, so this result presents the moderate relative activity in the extensive parts of the area.

Gachin and Hormoz island salt domes are composed of the Hormoz Formation and both are located in Hormozgan province and folded Zagros zone. Based on petrography, minerals of basaltic rocks formed in two stages: first magmatic minerals include in quartz, feldspar, pyroxene, amphibole, and then metasomatic minerals: tremolite - actinolite, chlorite, epidote, calcite, biotite, albite and iron oxide. Metasomatism changed rock forming minerals but most of clinopyroxenes are fresh compared to other minerals. Mineral chemistry of clinopyroxene is used for recognition of magma nature and tectonic settings of parent magma of the Hormoz Formation. The average composition of clinopyroxens of Gachin salt dome is augite (Wo27.66 En45.44 Fs26.91), clonopyroxens of Hormoz Island salt dome is augite –diopsid (Wo43.36 En32.71Fs23.93). These minerals are Ca-Eskola. Geochemical diagrams based on clynopyroxens composition show that the background of Hormoz salt dome samples are volcanic arc basalts and Gachin salt dome samples are intraplate tholeiitic basalts and they had sub-alkaline nature. Their forming temperatures of clinopyroxens are 875oc for Hormoz clinopyroxenes and 997oc for Gachin clinopyroxenes and forming pressure is less than 2kb.

The Upper Surmeh Formation (Upper Jurassic) consists of limestone, dolomite and interbeded anhydrite equivalent to the Arab Formation in the southern Persian Gulf. This succession is the main producing reservoir of the Jurassic system in the Arabian plate. This research was carried out based on core (thin section, porosity - permeability, capillary pressure data) and well log data to study the depositional environment and diagenetic effects on reservoir quality of the upper part of the Surmeh Formation. Petrographic investigations led to recognized nine microfacies which were classified in four facies belt including supratidal, intertidal, lagoon and shoal which were deposited in an arid homoclinal carbonate ramp. Diagenetic processes affected reservoir quality of identified microfacies. Among them, dolomitization, anhydritization and cementation are the main effective processes. Dolomitization increased reservoir quality but the anhydritization and cementation decreased reservoir quality. It is important to note that relevant reservoir quality is improved by development of shallow marine facies associations and secondary diagenetic events. Based on the porosity, permeability and mercury injection pressure data, anhydrite and anhydrite bearing mudstone have very low reservoir quality whereas ooid and bioclastic pack ston to grainstone have the best reservoir quality.