KHARAZMI JOURNAL OF EARTH SCIENCES (JOURNAL OF SCIENCE (KHARAZMI UNIVERSITY))
Year:2018 | Volume:4 | Issue:1|Papers Count:8

The north of Shahpasand Mountain Pluton, with the age of late Eocene – Oligocene, is located in the northwest of Saveh. Plutonic rocks of Shahpasand Mountain show a various composition of gabbrodiorite, diorite, monzonite, quartzmonzonite, granodiorite and granite. These rocks have granular, intergranular, porphyroid and poikilitic textures. The main minerals are plagioclase, pyroxene, amphibole, biotite, K-feldspar and quartz. The accessory minerals are zircon, apatite, sphene and opaque. From geochemistry, tectonic setting and petrogenesis point of view, the north of Shahpasand Mountain Pluton is compared with Silijerd pluton that is located in the northwest of Saveh. Spider diagrams show that a slight enrichment of LREE to HREE and also higher LILE relation to HFSE. Negative anomalies of Nb, Ti, P show the plutons belong to subduction zone. Geochemical data, suggest that the parent magmas of the studied rocks might be generated by crystal fractionation of arc basaltic magma in magma chambers, coupled with some crustal assimilation. The EPMA analyses on the plagioclase, biotite and pyroxene minerals in granodiorite and gabbrodiorite of the north Shahpasand Mountain Pluton show that plagioclase compositions in granodiorite are in the range of oligoclase to andesine and in the gabbrodiorite samples are from andesine to bytownite. The EPMA analyses of the pyroxene minerals show the existence of two types of pyroxene in the gabbrodiorite samples (orthopyroxene with hyperesthene composition and clinopyroxene with augite – diopside compositions), while in granodiorite clinopyroxene is augite – diopside composition. On the basis of geothermobarometry, crystallization temperature of pyroxenes are estimated to be about 800° C to 970° C and crystallization pressure 7 to 8 kbar for the pyroxenes.

Application of mathematics increasing in science in recent years, cause the mathematical models use to explain the geological processes. The researchers introduced a method based on mathematical calculations and algebraic model for metamorphic reactions. Pelitic metamorphic aureole is formed in North of Borujerd granitoid complex in the region east of Borujerd city. In this research for the first time, using a mathematical method for metamorphic reactions for high temperature of Pelitic metamorphic aureole based on algebraic model. Based on petrography, mineral assemblages of a rock are known and a thermodynamic system and components could be drive. SiO2, Al2O3, MgO, FeO, K2O and H2O Accepted as components and the system KFMASH chosen for calculation. Based on mineral assemblages, metamorphic reactions calculated using 6 by 6 and 6 by 8 matrices. Components put in Matrix and when Matrix’ s elements below the diagonal are zero, then the calculation is applied over the second matrix to find metamorphic reactions. Equilibrium reactions could be written based on both microprobe analyses and general mineral formula. The main reactions in the intermediate zones toward the contact, in order from low to high temperature, are cordierite formed after reaction of biotite, quartz and andalusite followed by equation of andalusite to sillimanite. Potassium feldspar appears in the same rocks with sillimanite. Potassium feldspar and cordierite formed close to the contact zone, Petrographic result confirmed paragenetic minerals which appeared in algebraic analysis. The results show that reactions constrain based on algebraic analysis, could be used to estimated pressure and temperature in petrologic grids.

The East Darreh-Baneh anticline is located in the Lurestan structural zone, west of the Zagros fold and thrust belt. In this zone thrust faults and detachment horizons have a main role in geometry and kinematic of the folded structures. In this research, deformational pattern and structural geometry of the East Darreh-Baneh anticline have been studied using interpretation of five 2D seismic profiles, drawing of structural cross sections, drilling well data in the adjacent anticline and related analysis. Accordingly, the East Darreh-Baneh anticline is a detachment folding, in which two upper and middle detachment levels is affected its structural geometry. In the study area, the shaly Garu and the flysch Amiran formations caused deformations as a middle and upper detachment levels, respectively. The high thickness of the upper detachment level caused formation of the anticlines in surface with low wavelength and amplitude and formation of the surface disharmonic folding on deep-seated anticlines. Also, geometrical parameters analysis of the East Darreh-Baneh anticline indicate that this anticline is an asymmetric and noncylindrical fold and from tightness view is open to gentle with wide aspect ratio.

Late Neoproterozoic Shotor Kuh metamorphic-igneous complex cropped out in 80 km southeast of Shahrood, include a wide range of igneous and metamorphic rocks such as metapelite, metabasites, metacarbonate, metapsammites and gabbros, olivine gabbros and diorites. In this study, the variations of magnetic parameters of high grade metapelitic rocks have been investigated during the migmatization and granitization processes. The carried out investigations indicate that the average magnetic susceptibilities (Km) decreased from 650 μ SI to 3 μ SI through the mentioned processes. This decrease is a reflection of the mineralogical and lithological changes, among of the decomposition-dehydration reactions of biotite and the conversion of biotite to orthoclase or muscovite in the transition from gneiss to granite. Garnet, biotite and with a lesser extent, opaque minerals (ilmenite or magnetite) are important magnetic carriers of the studied rocks. The average corrected magnetic anisotropy varies from 1. 008 to 1. 45 and also the shape parameter values of these rocks vary from-0. 44 to 0. 96. Based on the interpretation of magnetic fabric, most of the magnetic ellipsoids of gneisses are in oblate shape. The obtained magnetic foliations from the interpretation of magnetic data show a good corresponding with the measured magnetic foliations in the field.

Touyeh-Darvar granitoid pluton is situated in 50 Km SW of Damghan in Semnan province in the eastern Alborz zone. This pluton has intruded into the early Paleozoic rock units (Barout, Zaygun and Lalun Formations). Based on the field observations and petrographic studies, the pluton composed of monzonite, quartz monzonite and monzodiorite. Mineralogically, the pluton consists of plagioclase, alkali feldspar, quartz± biotite± amphibole. It’ s accessory minerals include ilmenite, magnetite, zircon, apatite, titanite and chalcopyrite and sericite, epidote, calcite, and chlorite are it’ s secondary minerals. The Amphiboles of the Touyeh-Darvar rocks are low pressure calcic type with ferro-hornblende composition and igneous origin. Application of the geothermobarometry methods yielded temperature ranges of 650– 730° C and pressures less than 2 Kb for stopping of exchange and final equilibrium of amphibole in the pluton that corresponds to less than 5 km depths for emplacement depth of the pluton. Existence of fine grained hyper-solvous to sub-solvous reaction textures (Perthitic, myrmekitic, graphic and granophyric) in the rocks of pluton and the lack of apparent contact metamorphism around it indicate diapiric ascend and emplacement of the pluton in a relatively cool and solid state in shallow depths of the crust. The Veins of mineral deposits such as Fe-Mn oxide-hydroxides, fluorite, barite, lead and zinc in the pluton host rocks are the obvious evidence for these states.

Quartzofeldspathic schists of the valley of Sovordydosha are situated in the shear zone of the north Shahrekord, in the central part of Sanandaj-Sirjan Zone. The metamorphic rocks show lepido-granoblastic texture. The most important of minerals are quartz, feldspar, and biotite. The samples indicate nature of greywacke to shale on the log (Na2O/K2O) versus log (SiO2/A12O3) diagram for their protolith. According to the geochemical characteristics, the source material of the rocks is the result of erosion, transportation, and deposition of evolved felsic igneous rocks and granitoid rocks. The average of the chemical index of alteration (CIA) and chemical index of weathering (CIW), as well as the binary diagram of Al/Na versus CIA show moderate weathering in during formation of the sedimentary protolith of the rocks. Moreover, based on SiO2 versus (Al2O3+K2O+Na2O) diagram, the paleoclimate of the region was dry at the time of the formation of the source material. The Mn* index and U/Th ratio determine oxidant conditions of the sedimentary basin in past time. Geochemical data indicate that tectonic setting of the protolith of the schists has been an active continental margin and continental arc.

The Dara anticline as one of the anticlinal oil structures in the Zagros fold-and-thrust belt within the Dezfol embayment (west of the Kazerun fault) has been carried out at this research. For this aim, after the determination of fold trend and mechanism, some sections at: NW nose, center and SE nose of anticline have been drown by using subsurface data. Analyses of folds exhibit the Dara anticline at Class 3 Ramsay classification. On the base of Fleuty classification, this fold is an open one. Fractures are at three main trends: E-W, N-S and NW-SE. Restoration sections indicate that the rate of shortening along the NW nose (A-Achr('39') section) is 6. 5% and at B-Bchr('39') section is 8. 4% that illustrates on high folding rate at SE nose of the Dara anticline.