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Mir Ali Asghar Mokhtari

فاطمه محمدی، محمد ابراهیمی، میر علی اصغر مختاری
سنگ شناسی و ژئوشیمی توده گرانیتوئیدی همیجان و سنگ های اسیدی همراه (جنوب باختر بهاباد، ایران مرکزی)
Petrology and geochemistry of Homijan granitoid and associated acid rocks (SW Bahabad, Central Iran)
Abstract


Abstract Studied area is a part of the Posht-e-Badam Block in the Central Iran zone, located 12 Km to the southwest of Behabad city. Igneous rocks of this area have exhibit a wide range of composition range from acidic to basic intrusive, sub- volcanic and volcanic rocks. Intrusive and sub- volcanic rocks of the studied area include the relatively large Homijan granitoid, Ferdows granitoid, gabbro- diorite stocks and Kuh-Siah sub- volcanic rhyolitic dome. The Homijan granitoid is composed of continues spectrum from a shallow-depth intrusion in the center to rhyolitic lavas and tuffs in the margins. The whole assemblage is covered by carbonaceous part (dolomites) of the Rizu series. There is not any metamorphic contact aureole in the contact of Homijan granitoid and the country rocks. Homijan granitoid contain porphyritic, porphyroidic and graphic textures composed of plagioclase, alkali feldspar and quartz phenocrysts in the fine- grained quartz- feldspatic matrix and marginal rhyolitic lavas have porphyritic and spherolitic textures with quartz and alkali feldspar phenocrysts. Rhyolitic tuffs have porphyroclastic texture. Ferdows granite has hetero-granular, graphic and perthite texture composed of quartz, orthoclase and plagioclase. Kuh-Siah rhyolites have porphyry, felsophyry and felsitic textures with small quartz and alkali feldspar phenocrysts. Geochemical studies demonstrate that Homijan and Ferdows granitiods along with marginal rhyolites of Homijan and Kuh-Siah rhyolitic dome have high- K calc- alkaline to shoshonitic nature and classified as S-type peraluminous granitoids with some tendency to I-type granitoids. Based on the spider diagrams, all rocks have similar trend which is indicative for their genetic relation. These diagrams indicate enriched LILEs (Rb, K, Th and Pb) along with negative anomalies of HFSEs (Nb and Ti). Chondrite normalized REE patterns demonstrate LREEs rich pattern with high ratio of LREE/HREE. The positive and negative anomalies of mentioned elements in the studied rocks probably are related to lower partial melting degrees of metasomatized mantle along with crustal contamination of this magma. Based on field investigation, petrographical studies and geochemistry and using the granitoid discrimination tectonic setting diagrams, it seems that Homijan granitiods and related acidic rocks was formed in the post- collisional setting within the Posht-e-Badam Block. Keywords: Homijan Granitoid, Kuh-Siah rhyolite, Behabad, Posht-e-Badam Block, Central Iran

 

 

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