ملیحه شاه زیدی

The Mishu granitoids occur in northwest of Central Iran and are part of the Khoy-Takab Precambrian metamorphic belt. Based on petrographic studies, this complex comprises several intrusions of granitic rocks ranging in composition from diorite to leucogranite. Geochemical studies indicate these granitic rocks can be divided into the three groups which have undergone a complex history of magmatic process. I-type and S-type granitoidic rocks and leucogranites generally having features typical of medium to high-K calc-alkaline to shoshonitic rocks. Primitive mantle-normalized trace element spider diagrams display enrichment in LILE and depletion in some HFSE which is typical of an enriched mantle source. Rb-Sr and Pb-Pb isotopic data determine the ages of 530±30 and 500±74 Ma for the rocks studied. S-type granites show high (87Sr/86Sr)i values between 0.7081 and 0.7104 and negative ɛNd values -4.18 to -4.72, whereas I-type granites have a much wider range in ɛNd of -0.8 to -4.3 and lower (87Sr/86Sr)i of 0.704867 to 0.708046. Initial ɛNd values for leucogranites range from .98 to .25. However, their variable Sr and Nd isotope compositions together with major and trace element geochemistry suggest that they were produced by mixing of crustal anatectic melts with variable amounts of mantle-derived basaltic liquids. The present study, therefore demonstrates that these granitic rocks formed on an active continental margin during convergence of Centeral Iran and Alborz-Azerbaijan to Arabian platform during Precambrian (closure of branch of the Proto Tethys Ocean).

The Mishu garnitoidic complex is cropped out in NW of Mishu mountains, in southwest of Marand, northwest Iran (East Azarbaidjan) which is intruded into Kahar Formation. Based on petrographic studies, this pluton is composed of intermediate rocks including granodiorite, quartzmonzodiorite and diorite. Plutonic rocks are mainly composed of quartz, plagioclase, orthoclase, biotite, amphibole and pyroxene minerals. Amphiboles are one of the most important minerals in intermediate rocks. Based on results of electron microprobe analyses, amphibole minerals are calcic and show magnesiohornblende to actinolitic hornblende and actinolite compositions. Also these Amphiboles have compositional zoning from magnesiohornblende, actinolitic hornblende or actinolite with cores of magnesiohornblende or actinolitic hornblende. Actinolite and actinolitic hornblende rims occured patchy compositional domains or crystal aggregates around subhedral cores of actinolitic hornblende or magnesiohornblende. The mineralogical studies show cores of phenocrysts crystallized under conditions of low oxygen fugacity, indicated by low Mg content.Whereas high Mg content in the rims displays higher oxygen fugacity during their crystallization. There is no evidence for actinolite or actinolitic hornblende resulting from late hydrothermal activity, nevertheless patchy domains of actinolite or actinolitic hornblende are probably the result of subsolidus reactions of clinopyroxene in the presence of exsolved fluid.

The Mishu garnitoid complex, located NW of Mishu Mountains, southwest of Marand and northwest of Iran (East Azarbaidjan), and intruded into the metamorphosed Precambrian rocks (Kahar Formation). Based on petrographic studies, the pluton composed of acid rocks including granodiorite, monzogranite, syenogranite and two-mica granite, all cut by acid and diabasic dykes. The presence of surmicaeous xenoliths are evidences of refractory minerals and restite. Petrographic and geochemical studies indicate that the Mishu plutonic rocks can be classified as S-type granite having calc-alkaline and peraluminous nature. On chondrite and primitive mantle-normalized diagrams, almost all the rocks show enrichment in LILE and LREE, HREE, HFSE depletion as significant negative depletion in Nb, Ta, Eu, Ti, Sr and Ba, which is typical of calc-alkaline magmatism from subduction-zone environment. The geochemical data and position of the studied samples on discriminative tectonic diagrams show that the rocks are compatible with orogenic granitoids.

The studied area is located in the north-east of Ardestan in Isfahan province. In Iran’s geological classification it lies in the central Iran zone. The volcanic rocks of the Kuh-e Dom area are predominantly rhyolite, rhyodacite, dacite, tuff, ignimbrite, andesite, banakite and basaltic-andesite. The major rock–forming minerals are quartz, plagioclase, alkali feldspar (orthoclase, albite), amphibole, biotite, clinopyroxene and olivine. Apatite, zircon and opaque minerals are common accessory minerals. Biotite, clinopyroxene, plagioclase, alkali feldspar and chlorite in various rock samples were chosen for electron microprobe analysis. The results suggest that feldspar phenocrysts show a large compositional range from andesine-labradorite to labradorite-bytonite in banakite and basaltic-andesite and oligoclase-andesine and sanidine in rhyolite and dacite. Clinopyroxene phenocrysts show a compositional range diopside to augite in banakite and basaltic andesite. Phenocryst of biotite in the studied rocks is essentially of similar composition, and they are phlogopite (Mg-rich). This observation suggests that clinopyroxene and phlogopite formed from a Mg-rich magma. Also mineral chemistry of volcanic rocks of Kuh-e Dom indicates that these rocks were generated from calc-alkaline to shoshonitic magma and are related to continental arc orogenic magmatism. Barometery of pyroxene indicates that this mineral formed from a water rich magma in pressure of 5 kbar. On the basis of geothermometery studies, crystallization temperature has estimated to be 720-800 °C for acidic rocks and 1170 °C for basic rocks. The geochemical investigations show two stages in Kuh-e Dom magma evolution: Stage I is represented by clinopyroxene and phlogopite formation in a magma chamber. Stage II of magma evolution is represented by crystallization of matrix during and after magma eruption. Probably sanidine with small amounts of apatite and magnetite crystallized from the quenched magma at this stage.