PETROLOGY
Year:2011 | Volume:2 | Issue:5|Papers Count:7

The Meskani ore deposit is located in the Central Iran and Anarak-Khur metamorphic area. Microscopic studies were conducted on polished, thin polished and double polished thin sections of quartz and calcite minerals from ore bearing veins. Chalcocite, Nickeline, Chalcopyrite, Rammelsbergite and Malachite were recognized which Nickeline is surrounded by Rammelsbergite representing deposition of nickel and increasing of arsenide in ore bearing solutions. Most of the studied fluid inclusions are from liquid rich two phases (L + V) type. Genetically, primary types were selected for this study. Based on freezing studies, calculated temperature of last melting point (Tlm) is from -1.6 to -18.5 °C that is equal to 2-22.5 % wt eq. NaCl. Heating studies have revealed a homogenization temperature (TH) range of 130-160 °C. Homogenization temperature - salinity binary plots show two distinct fluids that can represent two different phases of mineralization or two distinct different sources of ore bearing fluids. Probably one of them represents volcanogenic ore bearing fluid and the other represents basinal brine ore bearing solution. The geochemical analysis of collected samples from different parts of Meskani ore deposit, elements including Co, Ni, Cu, Zn, Pb, Th, U, Zr and Sr were determined among of them Co, Cu, Ni and U are the most important. Scatter diagrams of these elements were plotted and their correlations determined. Results of these analyses revealed that the average of U, Th, Ni, and Cu are 269, 26, 452, 10786 ppm, respectively. Another interesting feature is the inverse correlation between U content and Th/U ratio. This feature represents that high U content in these rocks is not related to magmatic differentiation. In contrast of vein samples, there is not any correlation between U, Cu and Ni changes in country rock samples. This is one of the specific characteristics of shoshonites and andesites that represent these elements have not been originated from country rocks. The geochemical and petrographical studies have shown that country rocks are mainly shoshonitic in composition.

The Loghar ophiolite is located in ophiolitic belt of Kabul block (southeast of Afghanistan) and it is a part of Neotethyan ophiolites in Alpine - Himalayan orogenic system with Eocene age. Olivine, orthopyroxene, clinopyroxene and spinel are rock forming minerals of Loghar ophiolite mantle peridotite. Most of the olivines from different rock types are serpentinized but some fresh are present with forsterite composition. Orthopyroxene and clinopyroxene are enstatite (Mg# 0.961-0.972) and diopside (Mg# 0.976-0.999) in composition. The Cr# of vermicular and unhedral spinels of lherzolite and subhedral reddish brown spinels of harzburgite are 0.547 and 0.625 respectively. The Cr# of subhedral to euhedral spinels of dunite is 0.477, induced by high content of Al2O3 and low level of Cr2O3. The Cr# of dark red and euhedral spinel of chromitite is 0.633. The peridotites of the studied area belong to sub-oceanic crust mantle. The low content of Al2O3 in pyroxenes (opx and cpx) and the low amount of Na2O in clinopyroxene indicate high degree of partial melting of mantle peridotites. The chemical compositions of minerals in dunites are different from that of lherzolite and harzburgite but present considerable similarity with that of the pillow lavas. The dunites of Loghar mantle peridotite (LMP) do not share features with those derived by partial meltiny, but represent sub lithospheric melt channels.

The south Qorveh granitoid plutons (Kurdistan) which have intruded into the regionally metamorphosed rocks (Kimmerian Orogeny) lie in 80 km NW of Hamedan city. They composed predominantly of granodiorite and granite with minor amount of diorite and gabbro. Field characteristics (i.e. absence of migmatite), as well as several petrographical and geochemical features including the presence of Ca-plagioclase, magnesio-hornblende, and the lack of Al-bearing minerals (i.e. corundum, muscovite), the ASI>1, mol Na+K>mol Al, ratio Na2O+K2O-CaO/SiO2, decrease of P2O5 in Harker diagram, as well as high abundances of Na and Ca are in favor of I- composition of the parent magma. To determine the tectonic setting of the Qorveh granitoid plutons, several diagrams are used including Rb/10-Hf-Ta*30, La/Yb vs. Th/Yb, Th/Ta vs. Yb, spider diagram, and also discriminating diagrams for tectonic environment. Using Agrawall, the studied granitoid has R>0 and so it is an orogenic granitoid. The studied samples generally reflect the volcanic arc setting in active continental margin and it is similar to late- orogenic granitoids. Investigation of tectonic setting and age of granitoids in Sanandaj-Sirjan Zone (SSZ) show that the granitoid developed by subduction of Neo-Tethyan oceanic crust underneath Central Iran.

The Takab metamorphic complex in the NW of Iran, is located between longitude 47o45' and 47o05' E and latitude 37o30' and 36o30' N. The Takab complex, with Neo-proterozoic- Cambrian age, displays tectonic, lithological, stratigraphic and geochronological feathres (relative and isotopic dating) similar to those of the Central Iran Zone. Therefore, it is considered as a part of the Central Iran Zone with similar age (i.e. Neoproterozoic-Cambrian). The types of metamorphic rocks in the complex are gneiss, calc-silicate granulites, mafic granulites, migmatite, amphibolite, dolomitic marbles, pelitic schists, basic schists and serpentinized metaperidotites. The olivine- bearing marbles are derived by dolomitic marbles metamorphosed under granulite facies. Based on the appearance of olivine in paragenesis of the dolomitic marbles, the pressure and temperature of pick metamorphism is estimated at T³800oC and P~8 kbar. The evidence for retrogression of the Ol-bearing dolomitic marbles is the presence of tremolite + dolomite assemblages after olivine. The infiltration of H2O-enriched fluids during retrograde metamorphism led to the formation of H2O-bearing minerals such as tremolite, zoisite and clinochlore as well as titanite in paragenesis of the dolomitic marbles.

The metapelites of Jandagh, (based on mineral assemblages) can be divided into four categories: quartz- muscovite schists, quartz- muscovite- biotite schists, garnet- muscovite-chlorite schists and garnet- muscovite-staurolite schists. Jandagh's garnet- muscovite-chlorite schists show the first appearance of garnets. These garnets are basically formed of 58-76% almandine 1-18% spessartine and 8-20% grossular. The microprobe analyses along the Grt in Jandagh's metapelitic rocks show that Mg number of garnets varies and increase from core to rim. This is a feature for prograde metamorphism of metapelitic rocks. The well-preserved garnet growth zoning is a sign that metapelites were rapidly cooled and later metamorphic phases had no effect on these. The appearance of staurolite in garnet- muscovite-chlorite schists signifies the beginning of amphibolite facies. The absence of zoning in the staurolite contained in these schists suggests the formation and growth of this mineral in a prograde metamorphism occurred at a widely spaced isograde. The thermobarometric study shows that Jandagh's metapelites were formed within a temperature range of 400-670 oC and a pressure range of 2-6.5 kbar. These results are consistent with the minerals' paragenetic evidence and show effect of metamorphism on Jandagh's pelitic sediments in the limit of greenschist and amphibolite facies.

The Talle-Pahlevani mafic-ultramafic intrusions located in northwest and south of leuco-quartz dioritic and anorthositic batholiths developed in the southwestern Sanandaj-Sirjan zone (173 Ma). These intrusions consist primarily of gabbro in association with veins and lenses of anorthosite, trectolite, clinopyroxenite, and wehrlite which show gradual and sometimes sharp boundaries with the gabbro. In the gradual boundaries, the gabbro is mineralogically transformed into anorthosites and wehrlites. On the other hand, in the sharp boundaries, the mineral assemblages in two sides are different. There is no clear deformation in the Talle-Pahlevani mafic-ultramafic intrusions. Hence, the changes in mineral compositions are the result of crystallization processes in the magma chamber. The chemical changes, especially for REE, from anorthosite and wehrlite veins and lenses toward gabbro in the gradual boundaries are continuous. The changes are presumably resulted from different crystallization processes in the different parts of the intrusions that cause crystallization of anorthosite, clinopyroxenite, and wehrlite cumulates in the intrusions. Rocks of the sharp boundaries show sudden chemical changes, but the changes exhibit the same patterns of increasing and decreasing of the elements, especially for REE. Therefore, it is possible that all parts of the intrusions were formed from the same parental magma. Parts with unequilibrium crystallization in the form of cumulus and sub-solidification, underwent fractures, and were interspersed throughout the magma chamber due to late injection pulses or mechanical movements. The geological and age data show that the intrusions generated from an Al2O3, Sr-, and FeO-enriched and K- and Nb-depleted tholeiitic basaltic magma likely partial melting 5-30 % wt. of the spinel-peridotite mantle within an incipient rift system. Then, the magma was crystallized in lower crust (relatively high P.) magma chamber.

Some intrusion bodies have been injected into the metamorphic complex consisting of green schist, blue schist and Garnet-amphibolite rocks in Soltan Abad area (NE Sabzevar). The intrusion bodies are trondhjemite in composition and display adakitic characteristics. Trondhjemitic melts that generated by metabasites partial melting or differentiation of mafic magma at the shallow levels of the crust consisting of usual minerals such as sodic-plagioclase + quartz ± amphibole ± biotite. Microscopic and field evidences, whole rock chemical composition of trondhjemite and adjoining Garnet-amphibolites blocks, thermobarometry calculations of adjacent metamorphic rocks and simultaneity of metamorphic and magmatic events indicate that metamorphism and partial melting of subducted oceanic lithosphere has occurred at the depth of a hot subduction zone, consequently adakitic melt and Garnet-amphibolite restite generated. The formation and crystallization of the melt at the deep levels, high rate of magma ascent toward the surface and the abundance of water-bearing fluids during emplacement caused crystallization and survival of an unusual paragenesis containing of quartz, albite, muscovite (magmatic and non-magmatic), epidote (magmatic and non-magmatic) ± garnet (magmatic) ± amphibole (magmatic and non-magmatic).