PETROLOGY
Year:2010 | Volume:1 | Issue:1|Papers Count:7

The metamorphic rocks of the Ghorveh area, southeast of Sanandaj, are classified as a part of the Sanandaj-Sirjan metamorphic zone. South of Ghorveh includes an assemblage of regional and contact metamorphic rocks as a result of intrusion of igneous plutons. Different types of metamorphic rocks are produced in this regard. Metapelites have two generations of andalusite, cordierite and garnet produced by two distinct contacts metamorphism. Fibrolites are associated with andalusite, garnet, biotite and muscovite near Sartip Abad intrusion. Fibrolite growth without deformation and randomly on biotite and andalusite shows that fibrolites have formed at the latest stage of intrusion phase in this area. The textural studies of fibrolites show that they are of disharmonious type. Thermobarometry shows pressure and temperature lower than 3 Kb and 700oC in KMASH sub-system, respectively. Some textural evidence are consistent with continuation of fibrolite growth after ductile deformation.

Falling down of pieces of garnet-biotite-kyanite schists from the Qori metamorphic complex (southern part of Sanandaj-Sirjan zone, northeast Neyriz) into the Tall-e-Pahlevani intrusion, with an initial composition of leuco-quartz diorite–anorthosite, led to these schists (xenoliths) undergo highly contact metamorphic degrees up to pyroxene hornfels facies, and hence were formed felsic migmatites. Melt volume size produced (leucosome) based on minor element geochemical modeling was about 50 to 70 vol. %. Some parts of the partial melts (probably <25 vol. %) were extracted from the xenoliths, joined each other, and produced small patches of the per-aluminous granites.

The Nabijan Cu-Au exposure is located in 20 Km southwest of Kaleibar. On the basis of structural classification it is situated in the zone of Alborz-Azarbaijan. The diorite-monzodiorite to gabbro-monzogabbro intrusive units of the area with Oligocene age, is intruded into the calcareous and volcanic rocks of the upper Cretaceous lead to metamorphism of the country rocks as well as the original body. Four hydrothermal zones including potassic, phyllic, silicification and tourmalization are recognized. Pyrite, native gold, chalcopyrite, arsenopyrite, sphalerite, chalcocite, malachite, azurite and hematite are present. Based on geochemical exploration studies and collection of 425 samples, the content of Cu varies from 41200 to 12 ppm. The average content of gold is 0.44 ppm. The formation and occurrence of Au and Cu mineralization are controlled by structural and geochemical ingredient.

The Qorveh Plutonic Assemblage (QPA) is located in south of Qorveh, about 80 Km NW Hamedan, between 47o 42' and 48o E-longitude and between 34o 50' and 35o 10´ N-latitude. It was emplaced in a Sanandaj-Sirjan Zone (SSZ). Mafic and felsic intrusions have been identified within the QPA and this paper focuses on the geochemistry of three main units of this assemblage. These units have been identified on the basis of field observations, mineralogical and geochemical characteristics consisting of diorites, granodiorites and granites. The gabbro-diorite plutons are characterized by SiO2 contents between 48 and 54 wt %, low abundances of incompatible elements (Ba, Nb and La) relative to mantle, but rather are similar to their average in the middle crust. In addition, they have Al2O3/(MgO+FeOt)= 0.98-1.54 and molar CaO/(MgO+FeOt)= 0.59-0.71 and they were probably derived from a mafic crustal source. The geochemical features combined with the high volume of the granitoid rocks (the granodiorite and granite) are inconsistent with an origin via the differentiation of mantle-derived basaltic parent magma and assimilation. The granodioritic and the granitic rocks show moderate values of molar Al2O3/(MgO+FeOt) and molar CaO/(MgO+FeOt) suggesting an origin involving dehydration melting of a metagreywacke source. Geochemical data on REEs, Y, Rb, and Sr in the latter units indicate that amphibole and plagioclase in the absence of garnet, were the major fractionating phases during magma segregation.

Field, mineralogical and geochemical investigations indicate that Qatruyeh area, northeast Neyriz, has experienced two different stages of metasomatic-hydrothermal alterations with dominance of magnetite mineralization. Replacement textures and mineral assemblages in host rock reveal that the mineralization and hydrothermal alteration occurred in two stages. The first stage of alteration includes of Na-Ca alteration accompanying magnetite ores with mineral paragenesis of Paragonite+Siderite+Titanite+Tourmaline±Tremolite±Pyrite±Chalcopyrite. Na-Ca alteration related to epigenetic ore mineralization tends to be developed in deeper levels along bedding. The second stage indicates a sericitic-propylitic alteration which occurred with widespread veins and veinlets of hematite. Mineral paragenesis consists of sericite+quartz+epidote+chlorite± magnetite. Analytical data on metacarbonate host rock show that LILEs and REEs were depleted whereas HFSEs were enriched during the alterations. Data from fluid inclusions suggest that low grade magnetite ores were deposited at temperatures between 180 and 435oC and pressures <280 bars from NaCl-MgCl2-CaCl2-H2O-CO2-bearing fluids with salinities between 3.5 and 15 weight percent NaCl equivalent.

The Astaneh granitoid massif represents a small portion of Sanandaj-Sirjan zone and consists of tonalite, granodiorite, monzogranite and rhyodacite, being the granodiorites the most dominant rocks. Petrological, mineralogical, field and geochemical investigations suggest that the Astaneh granitoid is similar to those of the high-K calc-alkaline series, metaluminous to weakly peraluminous, and displays features typical of I-type granites. Low Al2O3/ (FeO+MgO+TiO2) and (Na2O+K2O)/ (FeO+MgO+TiO2) ratios, and the trace and rare-earth elements patterns suggest that these rocks formed along a destructive plate margin and were derived from a lower crustal source. The granitoid magma involves partial melting of lower crustal protoliths (Amphibolites) and fractional crystallization of the melts in higher crustal levels generated the whole spectrum of rock types represent in the Astaneh massif. Mantle-derived basaltic magmas emplaced into the lower crust are the most likely heat sources for partial melting.

The volcanic complex of the (NE Nain) is part of Central Iran (Yazad block). This complex consists of intermediate to acidic volcanic rocks and includes dacite, trachyandesite, shoshonite and potassic trachybasalt Mineralogical characteristics such as chemical composition of clinopyroxene (diopside to augite), and high Mg number of biotites as well as geochemical ratios of Th/Yb, Ce/Yb, and Ta/Yb indicate that lavas are shoshonitic in nature. The lack of Eu anomaly is an indicative of high oxygen fugacity, a diagnostic feature of shoshonitic magmas. The pattern of rare earth elements and spider diagrams show LREE and LILE enrichment and HFSE (Ti, Ta, Nb) depletion which are the characteristics of subduction related magmas. Geochemical studies reveal that in addition to fractional crystallization, crustal contamination and magma mixing affected on the evolution of magma which has produced the volcanic rocks in the studied area.Based on the accomplished modeling, the source rock has possibly been a garnet amphibolite (including 0-10% garnet content) liable for generating the study volcanic rocks.