نشریه علوم زمین خوارزمی
سال سوم شماره 2 (پاییز و زمستان 1396)

Dalan and Kangan formations hosting major gas reservoirs in Persian Gulf Basin, are compartmentalized due to the intense facies and diagenetic changes in various scales. This means that the petroleum accumulation has been segregated into a number of individual fluid/pressure compartments. In this research by studying the sedimentology of Dalan and Kangan formations in one of the fields in the central part of the Persian Gulf, 11 microfacies related to 6 facies zone have been recognized. Based on petrographic studies, diagenetic processes affected these formations are micritization, dolomitization, cementation, stylolitization, compaction and dissolution. Then, according to sedimentological, porosity and permeability and formation pressure data, intra reservoir barriers have been identified and their potential as dynamic or static barriers have been evaluated. The results of this study show that in central part of Persian Gulf, there are 5 barriers in these formations that have the dynamic potential for reservoir compartmentalization. Anhydrite cements and chemical compaction processes are the main factors controlling pore destruction in these dynamic barriers. These barriers caused high pressure in upper Kangan and lower section of upper Dalan member. Determined dynamic barriers will have a fundamental role in field production patterns in different horizons

Ayrakan granitoid pluton with 12 km2 area cropped out in the northeast of Mohammad Abad Kooreh Gaz village from Khur o Biabank County and in the farthest NE end of Jandagh-Arousan Metamorphic-Igneous belt. The main part of this granitoid pluton consists of porphyroidic biotite granites. A few leucocrate aplitic granite dikes and apophyse as a late magmatic phase cut porphyroidic biotite granites. Both type of the rocks, suffered intensively plastic (mylonitisation) and brittle (catclastic or fragmentation) deformations. Porphyroidic biotite granites are supposed to show more intensive mylonitization. Based on geochemical characteristics, isotopic ratios of 87Sr/86Sri, 143Nd/144Ndi and εNd, Ayrakan mylonitized porphyroidic biotite granites and aplitic granites are belonging to peralumious S-type granites. , 87Sr/86Sri (0.712714 and 0.712490), 143Nd/144Ndi (0.5115227 and 0.511581), associated with negative εNd (-8.19 and -7.13) for porphyroidic biotite granites and aplitic granites, respectively, indicate that they are originated from melting of metapelitic lower crust. Based on, Zircon U-Pb dating, porphyroidic biotite granites and aplitic granites have 545±11 and 537±3.8 Ma age, respectively. These values confirm the earlier dating results (549±15 Ma age). Therefore, Ayrakan granitoids certainly are part of the basement and Iranian Gondwanan terrains with the Late Neoproterozoic-Early Cambrian age

Ring-type Eocene-Miocene alkali syenite-syenite intrusions of the North and West Sardasht are part of north Sanandaj–Sirjan zone. The syenitic rocks are located in the central part of the complex near the appinite-gabbro outcrops. Field and microscopic evidences indicate that magma mingling between alkali syenite and appinite-gabbro magmas has occurred to form intermediate parts as syenite in some outcrops. Felsic outcrops are mainly composed of alkali feldspar in the form of perthite. Enclaves of olivine, clinopyroxene, plagioclase, and amphibole along with a few opaque minerals and apatite were formed in the syenites. The main textures of the rocks are granular and lamination. The high ratios of (La/Sm)n and (La/Yb)n, high levels of K, Rb, and less Ba, and low concentrations of Hf, Nb, Zr, and Ta indicate the interference of an arc-related setting for the formation of the rocks. Geochemical and tectonic setting evidences show that the intrusions wereresulted by partial melting of the continental crust base of submature-mature (evolved) island arc or active continental margin formed as a result of hydrous-mafic magma injection of the mantle wedge upper supra subduction zone to the base. Geothermal gradient was high in the base of the subduction. By injecting the hydrous-mafic magma, widespread melting occurred, and the alkali syenites were formed. These tectonomagmatic conditions are confirmed by large-scale ring-shaped outcrops of the intrusions and mafic micro-granular enclaves. Finally subduction of Neotethyan oceanic crust under the other part of the crust or active continental crust, caused to form the Sardasht crust and then evolve this area over time to Oligocene. As a result of the continuity of the subduction, different rock types were formed around Sardasht

In recent years, fuzzy partitioning cluster algorithms have become more popular. Similar to crisp partitioning clustering, fuzzy algorithms can be used to integrate multiple models into a single zonal multiparameter model by grouping samples in a multidimensional space into clusters. The concept of partial cluster memberships integrates the structural heterogeneity of all input models and describes it in a fuzzy sense. In this study, the electrical resistivity data inversion is made by Gauss-Newton least squares method using RES2DINV software and also, the first arrival or break times are calculated using PickWin software, and moreover, the refraction seismic tomography data inversion is carried out using GeotTom CG software. Then, the data results have been clustered by three K-Means, FCM and Gustafson-Kessel FCM. Using Dunn index to optimize the number of clusters, the number of optimal clusters has been obtained equal to 12 that is a suitable number of clusters by considering the obtained electrical resistivity and refraction seismic tomography maps. Furthermore, considering the studies made in the dam site, alluvial basin and bedrock as well as bedding, it seems that Gustafson-Kessel FCM clustering method has shown better results. By starting Gustafson-Kessel algorithm and obtaining the results of running FCM, we see that the number of iterations is reduced and the speed of convergence is increased. The clustering algorithm computations in this research work have been made using programming in MATLAB software.

The felsic dyke swarm with the Late Cretaceous age is situated in the southwest of the Bayazeh village (South of Khur, Isfahan Province). This dyke swarm, with northeast- southwest trend, cross cut the Lower Cretaceous sedimentary rocks of the Biabanak Formation in the eastern margin of the Yazd block (Central East- Iranian Microcontinent). The Bayazeh dykes host the amphibolite and granulite xenoliths. Based on the mineral paragenesis, the amphibolite xenoliths are subdivided into the amphibolite, clinopyroxene amphibolite and garnet clinopyroxene amphibolite. Mineralogical study of these amphibolites indicates that they belong to the para-amphibolite type. Rock-forming minerals of the granulitic xenoliths in these dykes consist of plagioclase, phlogopite, spinel, garnet, sillimanite and staurolite. Mineralogical studies show that these xenoliths consist of Al-rich and Ca-, K-, H2O-poor minerals (except of phlogopite). Mineral chemistry of phlogopites in these granulites indicates their similarity to the micas from the lower crust xenoliths. According to the geothermobarometry calculations and mineral paragenesis, amphibolite and granulite xenoliths in the Bayazeh dyke swarm were derived from 21 to 32 km depths. Based on the Moho depth (approximately 40 km) in this part of the Yazd block, these xenoliths are fragments of the lower continental crust that have been carried to the surface by the felsic melts

Some Peridotite dismembered parts have outcropped in Southwest of Sahneh, as a part of Zagros ophiolite complex. These bodies contain olivine, pyroxene and spinel with some altered minerals such as serpentine and amphibole. Based on electron microprobe analyses, olivine composition is forsterite with Fo88-94. The composition of pyroxenes is diopside and clino­enstatite with low contents of TiO2 and Al2O3. The spinels are poor in Al2O3 with Cr# number between 0.41-0.51 which indicate the ophiolitic and depleted mantle origin. The serpentines have Al2O3 content in the range of 0.2 to 2.2 wt.% with SiO2 content between 34.15 to 44.07 wt.% and are chrysotile and lizardite. The low temperature of serpentine minerals (lizardite and chrysotile) and primary spinels indicates that the alteration was lower than 500 ºC. In the tectonic setting diagram, based on mineral chemistry, the higher content of Al2O3 and MgO in pyroxenes than to mid oceanic ridge ones and have the same properties with back arc basins. These evidences have been confirmed by spinel mineral chemistry. Accordingly based on the geodynamic situation of Kermanshah area and tendency of some samples to back arcs, it seems these peridotites have derived by high degree partial melting of depleted and sub-oceanic mantle in a supra-subduction zone-back arc and have same properties with residual mantle peridotites

Kamyaran ophiolite sequence as a part of the Kermanshah ophiolite-radiolarite belt is located in the northeast of Kamyaran, northwest Iran. No complete ophiolitic sequence is seen in this area and only a peridotite part including harzburgite, lherzolite and serpentinite is observed. The sequence is cut by some gabbroic dykes. According to the microprobe analytical data, olivine in the studied rocks displays forsterite (Fo) contents of 90.11 to 92.5. Their clinopyroxenes are diopside and augite. Orthopyroxenes in the mentioned rocks are compositionally enstatite with Mg# ranging from 0.91 to 0.92. The studied pyroxenes are rich in chromium, with 0.80-01.39 wt% chromium oxide. High contents of chromium in clinopyroxenes and orthopyroxenes are consistent with the degree of partial melting and the depleted nature of these rocks. The studied Cr-spinels are Al rich in composition and their average Cr# and Mg# are 0.37 and 0.69, respectively. From the mineral chemistry of harzburgites and lherzolites, it is inferred that the studied rocks are similar to the abyssal peridotites belonging to residual peridotites remained after extraction of mid-ocean ridge basalt (MORB) in a back arc basin setting.