فهرست مطالب ahmadi khalaji

The Takht iron deposit is located 120 km northeast of the Hamedan City in the Urumieh-Dokhtar magmatic belt. The Miocene Takht granodiorite intruded into the Cretaceous carbonates and resulted in Fe-skarn formation. Epigenetic mineralization in the Takht Deposit occurred predominantly as vein and lenticular ore bodies accompanied with argillic, carbonation, chloritization, epidotization and silicfication alterations and minerals including garnet, pyroxene, epidote, tremolite- actinolite, phlogopite, hornblende, quartz, calcite, magnetite, pyrite, specularite, chalcopyrite, hematite, limonite, goethite and malachite. Chemical composition indicates the presence of Si, Al, Ca, Mg, Ti and chalcophile elements such as Cu, Zn, As and Pb that originate from the coexistence of silicate and sulfide minerals with magnetite. The microthermometric results revealed homogenization temperatures (Th) from 153.2°C to 338.3°C and salinity from 0.827 wt.% NaCl eq. to 25.36 wt.% NaCl eq.. The δ18O (SMOW) values of magnetite were measured in the range of −0.46‰ to .31‰ and δ18O water is .1‰ to .9‰, respectively. These isotope values are similar to magmatic fluids that were also equilibrated with 18O enriched sources. The δ34S (V-CDT) values of pyrite show ranges of .3‰ to .5‰ and the original fluid δ34S H2S values were estimated ranging from .7‰ to .9‰. These positive δ34S values confirm that sulfur is provided by evaporate sulfates. During the retrograde stage of the Takht Skarn, re-mobilized metals accompanied with metal-bearing fluids (provided by intrusion) were mixed with sulfur-bearing descending meteoric waters and eventually, the mixing of the two fluids led to calcic Fe-skarn mineralization in Cretaceous carbonates.

The intrusive bodies of Almogholagh Batholith, in western Iran are emplaced into the Sanandaj–Sirjan magmatic-metamorphic zone and comprise three main groups: (1) gabbro-diorite, (2) quartz syenite, and (3) quartz monzonite, which crop out in most of the area. The quartz syenite and quartz monzonite rocks, having characteristics such as metaluminous, generally ferroan, alkalic to alkali-calcic types, high content of Na2O⭣, Zr, Ce, Ga, Y, Nb, Ta, REE, and depletion in Eu, Sr and Ti, show the features of borderline between A1 and A2-type granitoids with more A1-type affinity. On the basis of the results of the various diagrams, the gabbroic-dioritic rocks show between A1 and I-type granitoids nature with more I-type affinity. Distinctive peak patterns in spider diagrams accompanied by (La/Yb)CN values of 2.4 to 6.1 and Ba/La ratio >3 indicate magmatic activity in a volcanic arc environment, and the characteristics (Ba/Rb)CN 0.512638, εtNd >0, εtSr >0, high content of Nb, Ta and very high content of Zr (589 ppm) indicate that there was a subsidiary subduction after the initial collision for a long time and the magmas of Amogholagh batholiths were originated from mantle wedge, overlying the subduction zone or from mantle components around fragments resulting from delamination between continental crust and mantle lithosphere, demonstrating the involvement of subduction zone fluids, high flux of mantle-derived halogen-rich volatiles, and contamination within the crust during the petrogenesis of intrusions.

Varcheh gabbroic pluton is located in Markazi Province and is part of the Sanandaj-Sirjan zone. This pluton is gabbro to monzo-gabbro of alkaline nature. Based on condrite normalized spider diagrams, the REE pattern displays enrichment of LREE (100 times) and HREE (10 times). In addition, based on primitive mantle normalized spider diagrams, they display enrichment of HFS elements (Zr, Ti, P). Absence of negative anomaly of Nb is due to alkaline nature. Behavior of Zr, Nb, Yb, La, and Sm elements show that the primary magma is derived from enriched mantle by the partial melting of 10%-15% of the spinel - garnet lherzolite, respectively. This magmatism can be related to deep faults and crustal thickening by the Neotethys subduction. The Plagioclase composition in gabbroic pluton is in the range of oligoclase to labradorite and clinopyroxene composition is mainly diopside. The clinopyroxene composition shows that they were crystallized from an alkaline magma. On the basis of geothermobarometry, crystallization-temperature of diopside is estimated to be about 1150°C to 1200 °C and crystallization-pressure for the diopside is between 3 - 7 kb.

The studied area is located in the Binalud Zone and comprises Mashhad leucogranites (g2) that include pegmatites and tourmaline veins. According to studies of the Mashhad leucogranites¡ these granites are peraluminous¡ highly differentiated and resulted from melting metapelites. In these granites¡ tourmaline can be seen in various forms of dendritic¡ nodules¡ vein and pegmatitic forms. For geochemical studies of vein and pegmatitic tourmalines¡ it was used microprobe analysis (EPMA)¡ XRF and ICP- MS. Based on these analyses¡ pegmatitic tourmalines include schorl and vein tourmalines which are magnesium-rich- schorl and both are classified in the range of alkaline tourmalines. They have oscillatory chemical zoning and bluish green to brown pleochroism that is probably due to changes in concentration of Ti¡ Ca¡ and Fe. In the studied tourmalines¡ major substitutions took place including Na(Fe)= X-Vacancy and Na(Fe)OH=Na(O). Both types of tourmalines are resulted from magma differentiation with this difference that pegmatitic tourmalines show magmatic system characteristics but vein tourmalines have magmatic-hydrothermal system characteristics. These properties are related to the pegmatitic development stages and fluids obtained during their evolution.

The Nour Abad ophiolitic complex as south part of Kermanshah ophiolite is
located in the high Zagros zone. The high Zagros zone is divided into three sections including Bisotoun limestone, ophiolitic complex, and Bakhtaran radiolarite. The ophiolitic complex from lower part to upper part is composed of serpentinized peridotites, layered gabbro, isotropic gabbro, plagiogranite, sheeted dike complex, basaltic lava, andesite and sedimentary rocks, respectively. The petrographical studies have been showed that the primary minerals of the ophiolitic complex such as olivine, plagioclase and pyroxene are altered to serpentine, amphibole, chlorite, sericite and Feoxides secondary minerals. Also, mineralization in these rocks is contains chalcopyrite, bornite, malachite, azurite and titanomagnetite. Various alteration occurred in this rocks includes serpentinite, epidotic, silisic, sericitic, zeolitic, chloritic and carbonate. The results of chemical analysis for Nour Abad ophiolitic complex shows high concentration of Cr, Ni, Mn, Ti, Cu and Ag elements.

Metamorphic rocks are two groups of contact and regional in North West of Aligudarz. Regional metamorphic rocks in this area are composed from slate, phyllite, schists and contact metamorphic rocks are spotted schists and hornfels respectively. Petrographic studies of this rocks show that andalusite, cordierite and sillimanite minerals formed during of contact metamorphism. The geochemistry of theses rocks suggested that shale or greywacke is parent sedimentary rocks. The major and trace element show that igneous rocks (almost andesite) were primary rocks for these sediments. In comparison with average of upper continental crust, the rocks of studies area indicate of Rb, Sr, K negative anomalies cause to replacements of these elements during metamorphism and alteration. Discriminations diagrams of tectonic setting indicate a subduction zone (OIB). Based on the P-T pseudo sections and Bt-Sil- Cord, Bt-Sil and Sil-Cord paragenesis, for contact metamorphism estimated T and P were 650-670 ˚C and 3.5 Kbar respectively.

The studied area located in south and south western Arak town and are the part ofSanadaj-Sirjan Zone. The plutonic rocks in Astaneh and Boroujerd areas are quartz diorite,granodiorite and monzogranite. In addition to plutonic rocks, subvolcanic rocks of rhyodacite composition are present in Astaneh area. In general, in these areass mineral assemblage is the same in different units. The common minerals are amphibole, biotite, plagioclase and alkali feldspar, but mineral concentration is different in studied areas. Geological, petrographic and geochemical characteristics in these areas show that magma is calc-alkaline, high- medium K and metaluminous to peraluminous composition. Relationships of place, time, similar geochemistry and isotopic characteristics indicate that granites in two areas have cogenetic and same source nature. The most possible source for granitoid rocks in two areas are partial melting of lower crust amphibolites and sediments that occur in extended Boroujerd and small pluton in Astaneharea.

The results of microprobe analysis indicate four different kinds of amphiboles in Astaneh pluton and its subvolcanic rocks in the Sanandaj-Sirjan zone. The composition of these amphiboles in this area are magnesio hornblende in tonalite and quartz dioritic enclaves, actinolite in granodiorite and monzogranite, pargasite in dacititc enclaves and anthophillite in one tonalitic sample formed by replacement of orthopyroxene at the rim. All of the amphiboles crystallized at high fO2 which imply I-type nature. Application of different barometers and thermometers show that pargasite in dacitic enclave formed at higher pressure and temperature (767 °C, 6.6 Kbar) than the magnesio hornblende in quartz dioritic enclave (734°C, 2.8 Kbar) and magnesio hornblende in tonalites (708°C, 1.4 Kbar).

Boroujerd granitoid mass belongs to Sanandaj – Sirjan zone (SSZ). It consists of granodiorites, quartz diorites and monzogranites. The country rocks into which the Boroujerd granitoid was emplaced consist of greenschist rocks of the regional metamorphism.The statistical technique of discriminant analysis, using major element differences alone, shows that this mass has characteristics of orogenic granitoids (R>0). The Boroujerd granitoid has geochemical characteristics typical of arc intrusives e.g. I-type, high-K calc-alkaline series, metaluminous to weakly peraluminous, a greater enrichment in LILEs (Cs, K, Rb, U, Th) compared to HFSEs (Nb, Ta), depletion in Sr, Ba, P and Ti relative to other trace elements. High Th/Yb (>5) ratios correlated to high values (>10, up to ca. 100) for La/Yb and plot as volcanic arc granites on various discriminant diagrams. This granitoid is a typical representative of a volcanic arc environment, spatially related to an active continental margin. Crustal contamination processes provide a further complication in the interpretation of the Boroujerd rocks. The rarity of primitive magma compositions in arcs, particularly continental margin arcs, points to the important and consistent role of such processes. Probably, Boroujerd granitoid is the result of the subduction of Neo- Tethyan oceanic plate below the Iranian microcontinent.