نشریه پترولوژی
پیاپی 19 (پاییز 1393)

The study area is located in the Uromieh-Dokhtar volcanic belt and composed of andesite-basalt، andesite، dacite and quartz-monzonite as volcanic and subvolcanic. The occurrence of phyllic، argillic and propyllitic alterations point to the presense of hydrothermal fluids. The studied amphiboles have tschermakite and ferro-edenite composition. The compositional changes from core (Fe-Mg-Mn) to rim (calcic) refer to the variation of physico-chemical condition of magma in the last stage of crystallization. The biotites are assumed to be primary، their Fe/Fe+Mg ratio is over than 0. 33% and they are iron enriched. The composition of the chlorites plotted in the repidolite field with Fe and Si in the range of 6. 56% to 6. 76% and 5. 19% to 5. 61% respectively. The low content of Al+Fe3+ in sphene، can be the result of high temperature of its formation. The potassium content of the Kahang jarosites is more than that of the sodium indicating the hydrothermal-magmatic condition of these phases formation.

Subvolcanic basic rocks have been exposed in the north of Shahrekord، as a part of Sanandaj-Sirjan structural zone in the form of stocks and dykes in post Jurassic to early Cretaceous owing to their intrusion and emplacement into upper Jurassic volcano-sedimentary suite. These rocks are dolerites and show subvolcanic particular textures such as intergranular، intersertal and ophitic. The main constituent minerals of dolerites are plagioclase (Labradorite) which has altered to albite due to spilitization and clinopyroxene including augite and diopside. Secondary minerals are chlorite، calcite، epidote، clinozoisite and some minor minerals such as apatite، magnetite، titanomagnetite، ilmenite and sphene. Dolerites، based on geochemical and mineralogical signitures، are classified into the two distinct groups. The first group with tholeiitic affinity originated from an upper lherzolith source rock in a post subduction tension environment. The second group with alkaline and transitional nature generated from an eclogite source rock in an oceanic intraplate basalts environment. Dolerites have been formed after upper Jurassic or early Cretaceous due to their intrusion and translocation in the upper Jurassic volcano-sedimentary rocks.

In the northeastern part of Kurdistan province، there are many volcanic cones that are basaltic in composition. Petrographic investigations reveal these rocks are dominated by clinopyroxene and olivine phenocrysts and plagioclase and pyroxene micro crystals، while space between them is filled by opaque mineral and brown glass. The presence of zoned pyroxenes and sieve texture in these rocks are evidences of crustal contamination and magmatic unequilibrium. The studied rocks with 5-14% normative nepheline are alkaline nature. On Harker diagrams fractional crystallization is indicated by MgO decreasing while CaO، FeO، Ni، TiO2 and Cr and SiO2 increase. On discriminated diagrams the tectonic environment of the samples is inter continental extensional zone. Geochemical characteristics such as LILE، LREE enrichment، Nb، Ta and Y negative anomalies، positive anomalies of Ba، Pb، Th and Th/Yb enrichment suggest that the basaltic lavas studied derived from lithospheric mantle that contaminated by subduction fluids. Also، Zr/Hf and Hf/La ratios are evidence for upper crustal contamination. High (Th/Yb) N، (La/Yb) N and high Nb anomaly (0. 37-0. 98) show that the magma generated from a garnet lherzolitic source.

The Neyriz ophiolitic complex with NW-SE trend، is located parallel to and out of the Main Zagros Thrust. Mantle sequence of this ophiolitic complex، is comprising predominantly of harzburgite and minor lherzolite، dunitic sheaths and chromite pods. Base on petrographic studies، the essential minerals of these rocks are orthopyroxene، clinopyroxene and olivine; and chrome spinel is present as secondary phase. Geochemical studies show that these samples are enriched in refractory elements. On spider diagram normalized with the primitive mantle، large ion lithophile elements (LILE)، show enrichment relative to the high field strength elements (HFSE). On petrogenesis diagrams، the studied samples lie on island arc and supra-subduction zone environment. These features suggest a depleted source for these rocks، and are characteristics of magmas that formed at a marginal basin in a supra subduction zone environment.

There are various contact and regional metamorphic rocks، from low to high grade in contact of the Alvand plutonic body. These rocks have undergone regional dynamothermal metamorphism and in the later stage due to heat and fluids derived from the body have been subjected to contact metamorphism. Hornfelses from the east and the north-eastern part of the Alvand aureole have sedimentary protolith of shale type. In the studied hornfelses، garnets are almandine-rich; composition of biotite is sidrophyllite and of the plagioclase varies from albite to andesine. Based on thermometric cation-exchange method of garnet-biotite pair، using different calibrations، the obtained temperature for cordierite-free hornfels، is about 580 °C and for the cordierite-bearing hornfels 566 °C. In barometry with GPBQ system، calculated pressure for hornfelses is strongly consistent with pressure obtained from multiple equilibrium curves for these rocks and was estimated to be about 2. 9 to 3. 6 Kbar. The obtained temperature and pressure using composition from rim of minerals in cordierite- and aluminosilicate-bearing rocks، with multiple equilibrium curves and THERMOCALC software represent temperature of about 650 °C and pressure of 3 Kbar.

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 study area is located in the northern part of Khusf in Southern Khorasan province which borders the Sistan suture zone and the Lut block. Tertiary volcanic lavas outcropped in this area contain andesite، quartz andesite، dacite and rhyolite. These rocks are dominated by porphyric and glomeroporphyric textures. The essential minerals in andesitic rocks are plagioclase، amphibole and pyroxene set in microlitic groundmass in some samples. Rock forming minerals in quartz andesite and dacite include of plagioclase، biotite، amphibole and quartz phenocrysts. Rhyolites are composed of quartz، alkali feldspar and plagioclase. The presence of sieve texture، zoning، regrowthing rim، synthetic twinning in plagioclase crystals، rounded and embayed quartz and reaction rim in amphibole crystals refers to non-equilibrium condition during magma crystallization. Geochemically، the studied rocks are calc-alkaline and medium to high-K that are characterized by enrichment in LILE، the negative anomaly of Nb، Ta، Ti which indicate magma relation to subduction zone and active continental margin. Chondrite- normalized pattern shows LREE enrichment relative to HREE suggestsing the parental magma could have generated from partial melting of metasomatized mantle by fluid related to subducted sediments.

The Mahoor area is located، about 135 km south-west of Nehbandan in the center of Lut Block. The area comprises outcrops of Eocene volcanic and pyroclastic (Eocene) that were intruded by several intrusive rocks consist mainly of diorite as dykes and stocks. Chemical classification shows that plutonic rocks are gabbro-diorite، diorite، monzodiorite and tonalite. These granitoids are high-K calc-alkaline series and they are meta-aluminous. Magnetite suitability (1485×10-5 SI) mineralogical and geochemical features show that they belong to magnetite granitoid series (I type). Enrichment in LREE rather than HREE and enrichment in LILE rather than HFSE، and typical anomalies of Nb، Ta and Ti are important evidences that show the intrusions were formed in a mamgmatic belt of subduction zone. Eu element show negative anomaly and Eu/Eu* ratios are from 0. 65 to 0. 88. Negative anomaly of Eu is due to presence of plagioclase in magma source. Geochemical studies show that Mahoor granitoids are co-genetic and they formed in subduction zone and belong to calc-alkaline volcanic arc setting in active continental margins. Mineralization is present as disseminated and hydrothermal vein related to monzonite and diorite porphyry.

A metamorphic complex containing green schist، mica schist and serpentinite exposed in the Asalem area (NW Rasht). The occurrence of blue schist facies rocks in this complex are reported here for the first time. Mineralogical paragenesis of metabasitic blueschists consists of glaucophane، epidote، chlorite and phengite while there are garnet، phengite، chloritoide and feldspar in the metapelitic rocks. The metamorphic conditions of these rocks calculated by THERMOCALC software، petrogenetic grids and conventional thermobarometrs، are 7 to 12 Kb and 350 to 550 ºC for pressure and temperature، Pressure and temperature conditions of metamorphism and protolith diversity (metapelite، marble، metabasite، serpentinite) of the Asalem metamorphic complex indicate that they were created in the Pacific Ocean-type accretionary prisms (B-type blueschists). The studied metamorphic complex likely originated along the Paleotethys suture zone، as a result of the subduction onset of the Paleotethys oceanic basin beneath the southern margin of Luarasia during Carboniferous.