GEOSCIENCES
Year:2009 | Volume:19 | Issue:73|Papers Count:26

AyQalesi polymetal deposit is located 30 km southeast of Takab in Orumieh-Dokhtar structural zone. For Enzyme LeachSM analysis at the deposit, 723 samples were collected from B-horizon soils. Based on the analytical results and data interpretation, six oxidation anomalies, A through F, have been defined. Five of these are recommended as drill targets while one, anomaly C, is not recommended for drilling because it appears to represent a buried intrusion without significant Zn enrichment. Anomalies B, D and E have very high Zn values. For anomaly D, this is because of outcropping Zn mineralization and the presence of mine waste at surface. Anomalies B and E may occur above shallowly buried mineralized zones. Anomalies A, C and F contain much less Zn. Anomaly A may overlie a concealed zone of Zn mineralization that could be buried to a substantial depth. Anomaly F is not recommended for drilling because it appears to be a quite narrow mineralized zone.

The Zarrin area in the north of Ardekan is the part of Central Iran Zone. Some homogenous parts of Zarrin granite located in the shear zone changed to mylonites and ultramylonites. Microstructural evidence and deformation investigation show that chemical and structural changes occurred during the progressive deformation in mylonites. The most obvious chemical change is the noticeable decrease on Ti, Mg, Fe and P from mylonites to ultramylonites. Silica shows a slight increase in the mylonitic zone with progressive increase in modal quartz, but AI2O3 is nearly constant during the mylonitization. Because of decrease on feldspar porphyroclasts and feldspar grains in the matrix, compare to protomylonites, K2O decreases in mylonites. However, with relative increase on plagioclase, K-feldspar and epidote in the matrix, Ca, Na and K increase in ultramylonites. As a result of structural changes, quartz grains in weakly deformed protolith and protomylonite show recrystallization and sub grain. In a progressive deformation process, quartz in mylonites and ultramylonites reveals grain boundary migration in recrystallization. During the progressive deformation, K-feldspars become perthitic with fractures and plagioclases show kinking in their twins. With progress in deformation, recrystallization on K-felspar's margins and twins in plagioclase grains are formed. Based on structural evidence, temperature of 400oC has been estimated for deformation in Zarrin area in protogranites and protomylonites. The temperature continuously increases up to 500oC or more in green schist facies in the mylonites and ultramylonites.

The Caspian (Khazar) fault is the boundary between the Caspian plain and Alborz Mountain. As a major tectonic feature, this fault may be considered as the northern mountain front fault of the Alborz Range. Subsidence of the Caspian Sea in north, uplift of the Alborz Mountain, and its over thrusting on southern part of South Caspian basin has occurred along the Caspian fault. In this paper, a segment at the fault which is located between longitudes 52o 30' and 53o 00' - in the northern part of geological map of Qaemshahr - is considered as a segment that does not outcrop. This paper introduces the general structural and morphotectonic characteristics of this zone and describes the characteristics of the active anticlines (growing folds) and morphotectonic effects in this zone such as effects on rivers.

In basins of the northern part of Iran, combination of natural and human factors has intensified landslide and related numerous damages. The investigation importance of this phenomena and effective factors of landslide occurrence and also determining susceptible zones it order to preventing and avoiding its effects is required. At the beginning, of this research after field investigation, review of previous works in similar Lajemrood basin and using questionnaire, were recognized primary effective factors on landslide occurrence. Thin preparing effective factors maps in Geographic Information System. In order to quantifying the factors and weighting them, landslides percentage in different units was determined. For statistical analysis of multiple regressions the stepwise method was used which concluded with ignoring the elevation factor as regional model. Finally, geology, land use, slopes and distance from the road has the most effects on landslides. For evaluation of the accuracy of this model, neighboring basing (Varakee basin) with similar characteristics was chosen. The results have indicated that the most recorded area landslides in Varaki basin occurred in high and high hazard zonation. Thus, it can be concluded that presented model can be used for the study area.

Two cases of tungsten-copper vein-type mineralization have been studied in the Nezam-abad and Deh-hossein areas, in southwest of Shazand. The hydrothermal quartz-tourmaline mineralized veins have different host rocks (biotitic-granite and meta-sandstone). Considering similar ore metals (tungsten-copper-tin-lead-zinc) in the ezam-abad and Deh-hossein areas, same mineralogy of veins (quartz-dravite) and similar REE variation patterns in the two areas, it is suggested that the Nezam-abad and Deh-hossein mineralized veins have the same origin. It means, when the Br-bearing fluids were active, they caused the quartz-tourmaline vein-type mineralization in this area. Considering the barren intrusions in the area and other mineralogical-geochemical evidences in this study, it could be concluded that tungsten and other metallic elements in the Nezam-abad and Deh-hossein ore-bearing veins have a sedimentary/metamorphic origin.

Regional exploration of Kahang is located at 73 km of north east of Esfahan city and 10 km of east of Zefreh town. This deposit is located in Uromieh-Dokhtar volcanoplotonic belt. For the first time this deposit was investigated with using the satellite images processing (TM). Base on the primary study, such as field survey, geophysical study, R.S. and petrography and mineralogy investigation the region was founded suitable place for resources of Copper (Cu) and Molybdenum (Mo). Kahang region is an alteration and breccia zone. In generally, more than %99 of rocks of this region are affected by hydrothermal fluids become in the low and high alteration degrees. The rocks of the area include Andesite, porphyritic andesite, Dacite, porphyritic rhyodasite, Diorite, Quartz monzonite and porphyry micro granite. In plutons, from rim to center of massive, is a trend from basic to acid features with less age. For geochemical surveying, 174 soil samples in systematic method and 143 rock samples of the area have been collected. They are been analyzed for 45 elements using ICP - MS method in Amdel laboratory of Australia. After assurance of accuracy of the results, statistic parameters are calculated. Then correlation coefficient measures of data calculation using two and multi variables analyze methods. Thus, based on mean measures and standard deviation of normalized data of elements, anomaly of locations is distinguished and they are presented as a table. At this stage for separation and identification of important anomalies using P.N. method. For introducing of the best locations for excavation and also study of geochemical behaviors of Cu and Mo, anomalous maps of 10 elements drown include of Cu, Mo, Au, Ag, Pb, Zn, As, Sb, Mn and Ba. The anomalous maps are drown in first step based on standard normalized duet and percent measures and in the second step with threshold limits plus amounts of standard deviation. Accordingly, it is delineate that the most concentration ofhypogenous ores such as Cu and Mo in central part of area in Quartz monzonites and Diorites occurred, whereas the most concentration of supergeous ores such as Pb, Zn and Ag in the rim part of area in andesitic rocks occurred. Finally, for attainment of better results and recognition of anomalies correlated to ores, the composites haloes method is used and the map of composite haloes of supergene and hypogen ores are prepared based on standard nornlalized data. Solovov method is used for evaluation of erosion \W surface in ore area. On this base, if the amount of sum of standard normalized data of supergen ore to hypogens ratio is larger than one, we can conclude that the main ore bodies exist in the depth and it conserved from erosion processes.

In a perfect design of underground spaces, amount of total displacement from the point of stability analysis is fundamental. In empirical and numerical stability analysis periphery of excavated area is consider as a continued mass. When an underground space is excavated by blasting process, so periphery of tunnel is damaged by that process. As a result, those materials are not continued. In this research this area named "Crashed areola". 3 dimensional distinct element methods has more adapted with this area, while compared to other numerical methods. 3DEC 4.0 which is based on this method was chosen as a numerical codes. 10th kilometers of Gavooshan tunnel which is water conveyance tunnel is considered as a case study. The part of this tunnel which studied in this research is surrounded by ophiolithic gabbro rock mass. For modeling of this tunnel two conditions were considered, first with continue media of rock mass and second discontinue media so called crash areola. One of the advantages of this part of tunnel is installation of instrumentation with very scientific methods and absence of lining in the other band. The outputs of numerical solution were shown that modeling by considering crash areola is near to data collection by instrumentations.

Natural fractures are the main factor which control hydraulic behavior of oil and gas reservoir in naturally fractured reservoirs. Thus it is important to fully characterize these features in fractured reservoirs. Image logs are one of powerful tools in fracture study in wells. Image log is high resolution "pseudo picture" of borehole wall which records properties of fractures. In present study, FMI (Formation Micro Scanner) of two wells located in the same structural setting of a naturally fractured carbonate are considered. Well A and B drilled through three formations (Asmari, Pabdeh and Gurpi) and fracture data of these formations were acquired from these wells. Both wells located in the same structural setting near each other. We compared fractures of each formation in well A with well B to find out similarity and dissimilarity of fractures occurd in the same formation in different wells. This study shows that density and orientation of bedding planes of well A is completely similar to well B. Density of open fractures of well A is totally different from well B but orientations of open fractures are same in two wells. Density and orientation of filled fractures of well A are similar to well B. Pattern of fractures of Asmari and Pabdeh formations are similar but in Gurpi fractures are different. Comparison of density of bedding planes and fractures show that high fracture frequency occurred in the thin beds, for example FMI show that laminar intervals of Pabdeh coincide with highly fractured intervals.

The Tehran city, capital of Iran is located on young alluvium deposits which mostly cover due to rapid urban development. This urban development without proper geotechnical and geological assessment may cause great engineering and economic problems. Survey of geotechnical problems are one of the most important issue that consider for building important structures. Most of constructions are based on the ground. Hence the Examination and recognition of physical and mechanical properties of soil layers are so necessary. Present research aims to determine stability parameters, plat bearing and amount of foundation settlement in East and South-Eastern of Tehran in Ghalemorghi area. For this specific zones have been identified, among them, first, second and third zones have middle (2<qa<3), good (3<qa<4) and very good (4<qa<6) stability (bearing conditions). 4th and 5th zones show low (1<qa<2) and middle (2<qa<3) bearing condition. The 6th area has low (1<qa<2) and very low (0<qa<l) stability conditions. In a general view soil density decrease from north to south due to gradual change of sand and gravel deposits to clay deposit and with depth it increase. The amount of immediate settlement also decreases with depth. (Rezaei, Adib & Eivazi, 2007). Comparison between old and new researches show that in new researches, amount of plat bearing is more and amount of settlement less than old researches in surface layers (0-5 m), but there aren't any important changes in amount of plat bearing and settlement in deeper layers. We think increase in amount of plate bearing, and decrease in amount of settlement in surface layers have been caused by increasing and accumulation of constructions, and also increase of traffic in duration years. The further studies show that effect of loading decrease with depth. Amount of stability and settlement in each zone have important role to design and select the kind of foundation and layout depth.

The area is located about 230 km of southwest of Tehran. Based of geological observations, the plutonic rocks in the area consist of Neogene (Miocene) alkaline gabbro, gabbrodiorite, locogabbro and diabase. The Oligo - Miocene calc-alkaline extrusive rocks are dacite - ryodacite, andesite trachyandesite, hornblendandesite, basaltic andesite and trachybasalt. Studying on isotopic analyses of Nd and Sr indicate that surveyed area were contaminated with crustal rocks of Sialic composition .In isotropy geochemical studies, The Andesite samples are plotted in the limit of BSE; however, it seems that mantling rocks besides being settled in crust (esp. the upper continental crust) have been contaminated with in. The combination of BSE towards enrichment, from the proportion of 87Sr/86Sr has shifted; a sample of rocks shows this position. Spider diagrams related to trace elements of plutonic samples which are used for identifying the tectonic setting show intrusive are in the extensive regime; while the lavas don't have a steady trend and are similar to subduction zones. This shows that the intrusive of the investigated area are different genesis from the southern volcanic rocks.

Mehdiabad Zn-Pb-Ba deposit is located 110 km south-east of Yazd, in the Central Iran structural zone. The stratigraphic succession consists of three sedimentary formations of lower Cretaceous age. The Sangestan formation, the lowest unit of shale and siltstone with calcarenitic interbeded layers. This unit is overlain by ankeritic massive dolomite and dolomitic limestone of Taft formation. The Abkouh formation at the top is composed of cherty or clayey limestone with conglomeritic intercalation, lenses of massive reef limestone and calcareous shale. The structure of ore body shows a half-graben with a vast N-S syn form being complicated by the presence of poly phase faults. The main normal fault is Tappeh Siah fault, suggested to be active during and after the period of sedimentation. Major minerals are sphalerite and galena with minor pyrite, chalcopyrite in sulfide zone, smithzonite, hydrozincite, hemimorphite and cerussite in oxide zone. Mineralization occurs in stratiform-lenticular orebodies and concordant with host rocks. Also ore bodies showing laminated, disseminated, open space filling, karst filling, colloform and botryoidal textures.

Taftan is a stratovolcano, located to the SE of Zahedan, eastern Iran. Due to the highlands of the volcano, a microclimate is created in the region where precipitation provides some water in the arid region that the volcano is located. Field studies and chemical analyses of thirteen mine springs from western flanks of the volcano indicate that springwater in Taftan is somehow related to volcanic rocks. Based on hydrogeochemical analyses, significant variation in Mg2+(2-l50), Ca2+(11-465), Na+(10.5-444), K+(1.5-330), SO42-(8-1050), HCO-3 (0-353.8), NO-3 (1.1-58.6), CI-(10.65-1520) and mole fraction of SiO2 (6.11-182.87) all in mg/L is affected by the chemical composition of volcanic rocks. Since springwater in Taftan shows significant compositional variation, it is concluded that the springs originated mainly due to precipitation, affected by waterrock interaction to some extent. However, a few springs show characteristic of juvenile water and some may have a mixture of juvenile and meteoric water.

Tehran and its surrounding region are within affecting zone of some active faults of North Tehran and Mosha in north-north east and Parchin and Pishva in south. In addition, there are some other shorter faults and linear markers within the urban area of Tehran such as Niavaran, Mahmoudieh and Davoudieh faults in the northern part of city, and Rey and Kahrizak scarps in the south. Previously, according to occurrence of several historical earthquakes in Rey area and also some geomorphologic evidences, most of these markers with the linear scarps in south Tehran alluviums were mentioned as active faults. From seismotectonic and urban geology point of view whether these faults exist or not are an important issue. Recent seismotectonic studies including paleoseismology and geophysics investigations have failed to prove existence of such faults beneath the observed surface scarps. So in this paper according to delivered data from our paleoseismology, geophysical and seismotectonic investigations and also some geological evidences of foreland basin deposits (late Quaternary) in the Central Alborz (ex: shoreline evidences in Parchin area-south east of Tehran) and in some other place such Kordan fan (west of Karadj), we suggest that these scarps may be a kind of shoreline in front of the Tehran piedmont or the actual faults may be in different place than that suggested by observation of surface escarps. In this research we use satellite imagery (Land Sat, Spot, Quick birds), aerial photos and GPS kinematics to do Digital Elevation Model (DEM) through the Kahrizak scarp with paleoseismology trenching and geophysical (Geoelectric and Georadar) investigations on different parts of Rey and Kahrizak scarps.

Tirgan and Sarchshmeh Formations, Aptian age, belong lithostratigraphically to Kopeh Dagh, for many reasons, with reference to lithology and biology contents that can be compared with Orbitolina limestone in the Central Iran. The similarities between these unites were the reason to compare the Mozdooran section (Kopeh Dagh) with Baharestan section (Esfehan) by studying 71 lithology samples and 57 washing samples and found many similarities in lithology and biology. The similarities of environments and type of sedimentation basins, would command this possibility that Aptian to Albian sea of the Kopeh Dagh was spread out through the Central Iran. This result can indicate the close relation between the Kopeh Dagh and Central Iran in the aforementioned time periods.

Hashtsar ultramafic-mafic intrusive complex is located at about 20 km east of the Kaleybar city in the eastern Azerbaijan Province. This alkaline ring complex is formed by the penetrative of undersaturated and oversaturated different magmatic phases with Late Eocene to Oligocene-Miocene ages. Petrographical studies show that this massive consists of three main phases. The first phase is composed of magnetite mela alkali pyroxenite, plagioclase bearing alkali pyroxenite and mela alkali gabbro with coarse grained gabbroic dykes. The second phase consists of the nepheline bearing leuco gabbro - diorite to nepheline monzodiorite and nepheline monzonite, and the third phase is syenite and quartz-monzosyenite to granite with calk-alkaline affinity. Geochemical studies indicate that undersaturated phases are intensively enriched in trace elements, especially in LlLE and LREE. These magmas have generated from the parental magma with a potassic alkaline affinity from a metasomatic mantle. The different rocks types of undersaturated phases were produced by the liquid immiscibility, crystal fractionation and accumulation processes. The calc-alkaline magma of the third phase is probably resulted from the lower crust melting due to penetrative of first and secondary phases. Particular and ring emplacement of this complex is concluded by the eruption and discharge of huge and zoned magma chamber, after the caldera subsidence such as, volcanic string of Majid Abad formation in the Hashtsar region.

From June 2004 to December 2008 low seismic activity was recorded near North-Tehran, Taleghan and Kahrizak faults and inside of Tehran city. In contrast, seismic activity along Mosha, Garmsar and North-Alborz faults is considerable. Generally seismic activity decreases from 51 degrees longitude to west. Two earthquakes with 15 and 17 km depth were located in the west of Tehran city. The calculated focal mechanism for one of them is pure strike-slip. High seismic activity is observed along Mosha fault close to Damavand, Boumehen cities and Lavasant-e-Bozorg region. Calculated focal mechanisms along this fault includes both strike-slip, and reverse mechanisms that implies transpression motion, dominantly left-lateral slip along this fault that continued to Lavasanat region in south of the eastern end of the North Tehran fault. Precise location of some events shows depth range of 4-32 km. Generally, calculated focal mechanisms in studied region include both strike-slip and reverse mechanisms and seems that in southern part, approaching Central Iran, reverse mechanisms are dominant. It implies slip partitioning in southern margin of Central Alborz.

Shaley Pabdeh Formation (Paleocene-Oligomiocene) expanded in Fars, Khozestan and Lorestan. Lower Lithostratigraphical limit with Gurpi Formation recognized by purple shale. Upper Lithostratigraphical limith with Asmari Formation is transitional. In order to study sedimentary environments and sequence stratigraphy of Pabdeh Formation two stratigraphic sections were chosen (Zanjiran and Shahneshin). Petrographic study indicated 9 pelagic and calciturbidite microfacies. These microfacies in deep marine deposited. Calciturbidite facies were formed during sea level highstand, when high rate of carbonate production result in transportation of carbonate sediment in deep sea. Sequence stratigraphy study shows that Pabdeh Formation consists of two depositional sequences. In Zanjiran section lower and upper contact of first sequence is type two and upper contact of second depositional sequence is conformity with unconformity. In Shahneshin section the lower contact is type two and upper contact is correlative conformity with unconformity.

The crystallization history of a rock is recorded by the size and the distribution of its minerals. The porphyroblast crystal size in metamorphic rocks can give notable information about its growing medium. Considering the varieties of mineralogy in the Hassan-Abad's skarn and high frequency of garnet porphyroblasts in different metamorphic zones and special different sizes in the first metamorphic zone of the NE skarn, the crystal size distributions of this mineral is studied. With regard to this, digital photos of cutting surface were provided and analyzed by JMicrovision software. It has been expected, two different slopes can show three suspections: 1- parent rock composition effect; 2- crystal growing time; 3- fluid flow around plutonic rock. According to the presence of clintonite, vesuvianite and garnet and as many as joints in the region, the role of fluid in growing the size of garnet porphyroblast in part of the first metamorphic zone seem to be noticeable.

The Ziyarat Formation is an Upper Paleocene to Middle Eocene carbonate sequences, located in North of Tochal Village (south-east of Tehran), near Emam Zadeh Abdollah. The Ziyarat Formation with the total thickness of 212.5 m conformably overlies the Fajan conglomerate and is overlain by greenish tufaceous siltstone of the Karj Formation. Petrographic studies led to the recognition of 11 microfacies. Different faces and evidences such as the absence of reefal facies, calciturbidite deposits, and widespread tidal flat deposits indicate that the Ziyarat Formation was deposited in a homoclinal carbonate ramp environment. Micritization, cementation, compaction, neomorphism, dissolution, dolomitization, fracturing and silicification are the major diagenetic processes in the Ziyarat Formation, occurring in meteoric and burial diagenetic environments. Major and minor elements and oxygen and carbon isotope values indicate that Ziyarat carbonates were deposited in a shallow warm water tropical environment and original carbonate mineralogy was aragonite. Bivariate plots of Mn versus Sr/Ca and 8180 illustrate that Ziyarat limestones were affected by open system diagenesis with high waterlrock interaction. Early burial diagenetic temperature calculation based on heaviest oxygen isotope values of micrite and 8w of Eocene seawater of 0.85 SMOW, shows that temperature was around 39oC. Cathodluminescence studies of carbonate cements illustrated dull luminescence, because these carbonates affected by both meteoric and burial digenesis, and thus typical yellow to orange luminescence and zonation’s, evidence of meteoric digenesis, are absent. This statement is confirmed by isotropic evidences.

A three-dimensional lithosphere model with horizontal dimensions of 1500 kmx600 km and a depth extent of 70 km for the Zagros is constructed from available geophysical data to find out strength of the outermost layers in this area. The structural boundaries of the model are based on the results from the deep seismic sounding profiles. First the finite element model for the temperature is solved in order to obtain initial temperature and the geotherm, after that structural viscoelastic problem is solved using the same mesh as in the thermal initial condition. Preliminary results for wet and dry rheology indicate that the depth of the BDT is about 8 km and 11 km for hot geotherm and 10.5 km to 14 km for cold geotherm. The results are in good agreement with focal depth in the Zagros that most earthquakes occur in 8 to 15 km depth (Tatar et al., 2004 and Jackson et al., 2008), that the long-term strength of the continental lithosphere resided only in its upper part, which was contained wholly within the crust.

Determining and studying collected lithic assemblages, biota remains and deposited beds (regarding to sedimentology) of two rock shelters in the age of Late Pleistocene to recent interval in central Iran were the aims of this research. Mobarekeh (Qaleh Bozi) and Yekeh Chah (near Golpayegan) are two sites in which remains of consumed and hunted biota by human were checked by this research. Lithic assemblages are studied considering their sources. Mousterian lithic assemblages from Qaleh Bozi caves and rock shelters (Hassan Abad Caves) are made of silica pebbles (limestone with Nummulite or cherty beds in the age of Paleocene to Eocene time interval) that hominids had collected from the Zayandeh Rud River in the Middle Paleolithic Period. Finally it should be stated that lithic artifacts in Yekeh Chah are mostly Quartzite sandy shale (probably belong to Jurassic). Black beds (charcoal lenses) in Qaleh Bozi and Yekeh Chah caves were sampled and washed for Detemining biota remains and sedimentary components. All washed samples from two localities had remains of: burned wood (charcoal), large vertebrate mammals (mostly horse), vertebrate and micro vertebrates (fish, rodent, reptile and amphibian), egg of birds, seeds and grass. SEM photos related to hunted and consumed birds' beak and nails from Mobarekeh and Yekeh Chah con finned that the food of man in those localities could be similar. This research is first report the presence of hunter-gatherer horn inids in Central Iran (Mousterian). Lithic assemblages are collected from Separab Naein in the age of Mesolithic and from Tapeh Ashena (Chadegan) in the age of Neolithic as well.