seyed jamal sheikhzakariaee

The Plio-quaternary sub-volcanic domes are the products of magmatism in the Turkish-Iranian plateau in the collision zone between Eurasia and Arabia. Intermediate-felsic volcanic rocks are found 50 km west of Ardabil. These volcanic domes make a significant part of the Sabalan volcanic, a Plio-quaternary stratovolcano in northwest Iran. The igneous rocks (adakitic) include dacite, trachyte, andesite, trachy-andesite, and trachydacite, associated with ignimbrite and pyroclastic equivalents. They mainly comprise phenocrysts and a microcrystalline groundmass of pyroxene, amphibole, and plagioclase, with biotite and titanomagnetite. These rocks are enriched in Light Rare Earth Elements (LRREs) and Large Ion Lithophile Elements (LILEs) and depleted from Heavy Rare Earth Elements (HRREs) and High-Field Strength Elements (HFSEs). In these rocks, the SiO2 content is 56-66 wt%, Na2O is > 3.5 wt%, Al2O3  > 15 wt%, Yb < 0.2 ppm, and Y < 7 ppm, which are typical of high silica adakitic rocks. The initial ratios of the 143Nd/144Nd range from 0.5127 to 0.5129 and the initial ratios of 87Sr/86Sr for the adakites range from 0.7035 to 0.7060, reflecting the heterogeneity of the mantle and different degrees of crystallization. These geological, geochemical, and Sr, and Nd isotopic data indicate that these rocks belong to the post-collisional adakite type, and are derived from low-degree partial melting of a subduction-metasomatized continental lithospheric mantle (eclogite or amphibolite garnet). In the studied area, mineralization related to Plio-quaternary adakitic rocks has not been observed.

In many cases some barriers like low permeability, secondary porosity and decreasing in formation permeability due to damages casued by drilling, asphaltene and other problems confine oil production rate in unacceptable region and These problems reduce percentage of oil recovery from these reservoirs, These problems can be solved by utilizing hydraulic fracture method. A new model based on cohesive zone method coupling stress-seepage damage filed is developed to simulate the interaction between hydraulic fracture and natural fracture with using ABAQUS software. The effect of differential stress and approaching angle on the intersection between hydraulic fracture and natural fracture, as well as the effect of natural fracture cementing strength on the geometry of  hydraulic fracture propagation, have been investigated. While the hydraulic fracture initiates, propagates, and intersects with the natural fracture, it can either deflect into it or cross it by severing the natural fracture. The greater the approaching angle and differential stress , the easier it is for the hydraulic fracture to cross the natural fracture.The behavior of hydraulic fracture changes from deflection to crossing as the natural fracture cementing strength is increased.

In this investigation, the foraminifera and oligosteginids of Sarvak Formation (Late Albian-Middle Turonian) at the Khumi Anticline section (East of Izeh Zone) has been studied. It consists of limestone of 213m thick which overlies the Kazhdumi Formation conformably and underlies the Gurpi Formation unconformably at Khumi Anticline. The biostratigraphy of Sarvak Formation in this section indicates 80 genera and 39 species (19 genera and 49 species of plankton foraminifers, 17 genera and 22 species of benthic foraminifers and 8 genera and 4 species of oligosteginids). Based on received paleontological data 8 biozones and 2 subzones in study area were established: Pseudothalmanninella subticinensis Partial range Zone (Late Albian), Pseudothalmanninella ticinensis Interval Zone (Late Albian), Thalmanninella appenninica Interval Zone (Latest Albian), Rotalipora globotruncanoides Interval Zone (Early Cenomanian), Thalmanninella reicheli Total range Zone (Early to Middle Cenomanian), Rotalipora cushmani Total range Zone (Middle to Late Cenomanian), Whiteinella archaeocretacea Partial range Zone (Latest Cenomanian to Early Turonian), Whiteinella archaeocretacea Interval subzone (Latest Cenomanian), Dicarinella hagni Interval subzone (Early Turonian), Helvetoglobotruncana helvetica Interval range Zone (Early Turonian- Middle Turonian). Based on these biozones the age of Sarvak Formation in Marin section is Albian-Middle Turonian.

The study area is located in the Eastern Alborz zone (Gansser, 1951) which is a part of the northern margin of Gondwana during the Paleozoic (Stöcklin, 1974; Salehi Rad, 1979; Berberian and King, 1981; Şengor, 1990; Alavi, 1991, 1996; Stampfli and Borel, 2002; Allen et al., 2003; Horton et al., 2008; Sinha, 2012, 2013). According to studies conducted by Gansser (1951) and Hubber (1957), the gabbro masses of South Gorgan (Nahar Khuran Valley) belong to the ophiolite collection. Meanwhile, 6km South-East of Galougah city, Gorgan schists have been covered by underlying Jurassic sandstones with s steep discontinuity. The parts resulting from the erosion of Gorgan schists were observed in the sequence conglomerate of the underlying Jurassic. At the beginning of the Ziarat Valley, about 800 meters above the Nahar Khuran, two small tectonic masses (the thickness of about 11 meters) are placed on the layers. These masses are mostly metamorphic. The metamorphic rocks (Gorgan schists), as one of the important geological units in Iran, are mainly formed from low-metamorphic rocks such as slate, phyllite, chlorite schist, greenschist and micaschist along with volcanic rocks and gabbrodiorite masses infiltrating them.

To prepare a geological map of the study area, field sampling and fieldwork were first done from the various units in the region. Over 100 samples were collected from the area. Approximately 70 thin cross-sectional samples of the tectonic rocks of the area were selected from them and investigated using a polarizing microscope. In this paper, 11 points of clinopyroxene were selected for microprobe analysis. The point analysis done on these minerals was conducted using the EPMA method using a microprobe analysis set in the Center of Mineral Processing of Iran (Karaj). The structural formula is calculated using the Excel (Spreadsheet) and dividing them was done by the MinPet 2.02 software package. Given that microprobe analysis is unable to distinguish Fe2+ and Fe3+ and given that it reports total iron as FeO*, it is necessary to separate these two from each other in order to calculate the minerals’ structural formula.

Petrographic studies identified rocks including gabbro, olivine gabbro, monzonite, gabbro to monzogabbro altered, metagabbro, and catalactic porphyry diorite. Mineralogically, these rocks consist of phenocrysts of plagioclase with labradorite composition, clinopyroxene and olivine with accessory minerals of apatite, sphene, biotite, and metal minerals. Secondary minerals are chlorite, sericite, clay mineral and epidote. The dominant textures in these rocks are granular and ophitic. The results of electron microprobe analysis of these clinopyroxenes show that they have augite compositions. In addition, gabbros also mostly show alkaline composition.

To precisely investigate the rocks in the research area, the results of the chemical analyses of minerals were used in determining their petrogenesis. Felsic minerals mainly include altered plagioclase, the main combination of which is labradorite and which is converted to the secondary albite due to hydrothermal alteration processes. The combination of clinopyroxenes available in the volcanic rocks is in Quad range and has a composition of augite. The temperature calculated for the clinopyroxenes in gabbros is 1277.7 to 1353.1°C and the pressure is more than 10 Kbars.  (On the baseline of 3.65kbar per 1km in depth), the formation of clinopyroxenes in the parent magma was over 37km. The primary water content of the gabbro magmas is estimated to have been between 0.5 and 5 wt.%. Distribution of aluminum in tetra and octa positions of clinopyroxenes depends on pressure and the amount of water available in the crystallization environment. Accordingly, the amount of AlIV decreases as the amount of water increases. Tectonomagmatic diagrams suggest that the host rocks are alkaline and are related to volcanic arc setting.

Momen Abad mining district is a part of Eastern Iranian bentonite zone, located in Eocene-Oligocene volcanic belt. Mineralogical study of bentonites by XRD method introduced smectite and cristobalite as major mineralogical phases and plagioclase, alkali feldspar, paragonite, zeolite (heulandite and clinoptilolite), mica-illite, and quartz as minor phases. SEM imaging of bentonites shows that platy particles of bentonites form flocculated aggregates and occur as rounded and angular particles with cornflakes texture. Energy-dispersive X-ray spectroscopy indicates that bentonite aggregates are of Na-montmorillonite type. The rheological test results reveal that the apparent viscosity, plastic viscosity, yield point, and gel strength of simple bentonites of 30.4 g weight is higher than that of samples with 10.8 and 22.4 g weight; however it is not in accordance with API standard therfore is not appropriate for drilling industry. Rheological characteristics and gel strength for activated samples are better than the simple samples. It is noteworthy that fluids containing carboxymethyl cellulose polymer is the best material to increase the rheological characteristics of bentonites among the polymers due to high ionic properties of particles and they are applicable in oil drilling industry (samples B02 and B04). However, sample B07 with all additives is not compatible with API standard of drilling qualification. Among three bentonite samples, the rheological properties of apparent viscosity, plastic viscosity, yield point, and gel strength in 10 seconds and 10 minutes in simple bentonite of B02 with 30.4g weight are 8.5, 5, 7, 5 and 5 respectively and will be increased to 25, 9, 32, 14 and 11 respectively with carboxymethyl cellulose polymer showing the highest quality in accordance with API standard and is appropriate for drilling industry.

Sabalan volcano is located in the northwest part of Iran and 25km south of Meshkinshahr in the west Alborz-Azerbaijan structural zone. The rocks forming the Sabalan and its eastern and northern slopes are covered with significant amounts of white-gray pyroclastic deposits, which is indicating a very intense explosive activity at the last stage of this huge volcano activity. After conducting field studies and analyzing the results obtained using the mathematical calculations, a Plinian eruption was detected, and the extrapolated volume of the latest pyroclastic fall eruption was estimated 3.24 km3, and the eruption of Sabalan rated a VEI of 5. Also, due to the shape of the isopach curve, the role of wind in dispersing these deposits is from the west to the east. Also based on geochemical data, the Sabalan’s ignimbrite was rhyodacitic with calc-alkaline signatures and the high ratios of Ba/Nb>28 and Ba/Ta>450 are consistent with subduction related zone.