akram sadat mirlohi

On the base of petrology, the Mirabad- Chehel Khane granitoid, east of Bouin-Miandasht, dominantly consists of syenogranite, monzogranite, alkali granite and granodiorites. The main minerals of these rocks are quartz, alkali feldspar (Orthoclase), plagioclase (Albite - Oligoclase), biotite, ± amphibole with minor amount of allanite, zircon, titanite, apatite, ± tourmaline. The biotite from the granites are Fe-rich type (annite) and primary magmatic in origin. The composition of the biotites studied principally falls in the calc-alkaline subduction related I-type granite on the tectonomagmatic discrimination diagrams, which stand on their major element oxides. Which is consistent with the nature of their host rocks. The studied amphiboles are classified as calcic (ferro-hornblende) which points to the I-type nature of the granitoid. The tourmaline composition plots on the schorl - foitite field. The temperature for the alteration, on the base of chlorite composition from the syenogranite, is estimated around 350°C and from the monzogranite rocks about 341°C. Based on the application of Al-in amphibole, a 3 Kbar pressure was determined for the syenogranite unit corresponding to the depth of 8-11 Km for the emplacement of the pluton. Hornblende- plagioclase thermometer shows 694 to 700°C for the equilibrium of these two minerals.

The Ghaidou monzogranite in the southeast of Khomein constitute a part of rock complex from the northern part of the Sanandaj-Sirjan zone. This body intruded into the Jurassic micaschists and created a metamorphic aureole. Also، aplitic veins، tourmaline bearing pegmatitic dikes، felsic microgranular enclaves and surmicaeous enclaves are observed in this area. The predominant minerals of these rocks are K-feldspar (orthoclase and microcline)، Na-plagioclase (Albite- oligoclase in the monzogranite and oligoclase in the felsic microgranular enclaves)، quartz and black mica (Annite) -as the main minerals- with minor amount of tourmaline (schorle)، garnet، white mica (phengite)، sillimanite، kyanite، zircon، apatite and ilmenite. On the basis of biotites mineral chemistry، these phases are enriched in FeO and Al2O3 and relatively low in TiO2. These minerals are magmatic and primary and thermometry results yielded 660-690 ºC. According to the chemical composition of primary igneous biotites in the enclaves and monzogranites، these rocks have calc-alkaline، peraluminous and an orogenic continental collision affinity characteristics of S-type granites. Also، the biotite composition and the presence of ilmenite point to low oxygen fugacity and redox conditions during magma crystallization. Based on the available data، the generation of these rocks can be related to Arabian-Eurasia collision zone.

The Eocene volcanic rocks in the SW Jandaq that outcrop in the south of Doruneh fault constitute a part of the Central Iran zone. The predominant rocks consist of basalt andesite، trachyandesite and dacite that porphyritic، microlitic porphyritic and hyaloporphyritic textures are common. The essential minerals are represented by intermediate plagioclase، diopside، augite، phlogopite and magnesiohastingsite and the secondary minerals are Fe -oxide and chlorite. Based on geochemical data، these rocks belong to high-K calc-alkaline and shoshonitic series which with K2O، Ta/Yb، Th/Yb and Ce/Yb. Lava eruption in subduction setting can be demonstrated by highly negative Nb and Ti anomalies، and also by comparison with mantle normalized trace element trend with that of the volcanic arc. In addition، the discrimination diagrams (TiO2/Al2O3 and Zr/Y) display a continental volcanic arc setting for these rocks. The REE patterns (chondorite normalized) and their ratios plus positive Pb anomaly، point to the effective role of low grade partial melting of a metasomatized mantle and garnet amphibolites source accompanied by crustal contamination in the course of formation these rocks.

The Ochestan granitoids are located 60 Km South of Mahallat in Markazi province and in Sanandaj-Sirjan zone. Based on petrographic studies, these rocks are alkali feldspar-granite, granite (syenogranite and monzogranite) and granodiorite. Alkali feldspar (orthoclase and microcline), plagioclase (albite and oligoclase), quartz and muscovite are present as the major minerals and tourmaline, biotite, zircon, garnet, apatite, opaque minerals, rutile and chlorite as the secondary ones. Foliation is found in many parts of the pluton indicating mylonitization process. Geochemical studies show sub-alkaline (calc-alkaline), peraluminous and S-Type for the granitoid studied. According to spider diagrams, upper crust is considered as the magma source, and syncollision as the geotectonic setting. Partial melting of metapelites can be assumed as a source of magma generation in regard to the type of granitoids, geochemical data and metamorphic rocks exposing in this area.

The Jahagh anticline is located at 40 km south of Kashan and east of Ghohrud village. The Early Paleozoic volcanic rocks are outcropped in the Jahagh anticline core. Despite low degree alteration and metamorphism that are identified by mineralogical studies, the primary textures are well preserved whereas mineralogical composition has changed. The major minerals including of plagioclases and rare Fe-Mg minerals have experienced alteration. The presence of secondary minerals such as albite, chlorite, epidote and calcite shows that the low-grade metamorphism have occurred under greenschist facies. Following the intrusion of Ghohrud granitoid, the adjacent volcanic rocks have been metamorphosed under hornblende - hornfels facies. This phenomenon is evidenced by the association of plagioclase (oligoclase - andesine) and amphibole (Ferro -Tschermakite) in the rocks of western parts (approaching the intrusive mass).