نشریه پترولوژی
پیاپی 21 (بهار 1394)

The Alishar Cu-Au index is located in the Markazi province within the Uromieh-Dokhtar magmatic belt. The mineralized zone is hosted by andesitic to andesite basalt lava units، andesitic-andesite basalt tuff and rhyolitic to dacitic tuff (Eocene-Oligocene). The area is affected later by young granodiorite and monzodiorite plutonic units (Oligo-Momiocene). As a result of hydrothermal alterations، phyllic and propylitic alterations as well as kaolinitization and silicification developed in the area. In addition، Cu -Au mineralization has been introduced into the area، mainly associated with silicic veins. Based on geochemical data the Cu and Au contents of the samples are about 0. 5% and 0. 3 ppm respectively. Also، the Bi content of the studied samples is about 0. 5 ppm. The index comprises oxidation، hypogene and supergene zones and contains chalcopyrite، pyrite، chalcocite، magnetite، hematite، goethite and malachite. Fluid inclusion studies of the samples taken from silicic veins show that the homogenization temperature and salinity vary between 200 to 300 °C and 21. 6% wt NaCl respectively. On the base of obtained data، it can be concluded that the dominant mechanism for mineralization is the mixing of hydrothermal solutions with meteoritc waters. Geological، mineralogical and fluid inclusion investigations have demonstrated that mineralization in this area is correlated with other IOCG deposits in the world.

The Khalkoh bentonite mine is located in Ferdows، southern Khorasan province. In this research، genesis of Khalkoh mine was determined using mineralogical and geochemical studies. Analytical methods including x-ray diffraction (XRD) and chemical analyses (XRF and ICP-MS) performed on bentonite and country rock samples as well. The studied bentonites consist mainly of sodium montmorillonite. They also contain cristobalite، quartz، albite، calcite، halite and illite as minor phases. The stratabound nature of minerals، high amount of montmorillonite، the presence of gypsum layers alternating with bentonite and the lack of hydrothermal alteration indicate that bentonite deposit was formed in the diagenetic process by means of volcanic glasses alteration to bentonite in the lagoon. In spite of leaching of alkalies، the Si has not been leached from the system. This is supported by the presence of opal-CT and quartz and generally، shows the low fluid flow rate in the system. Based on the geochemical data، the parent magma and rock series are rhyodacite/dacite and calc-alkali series، respectively، formed in volcanic arc setting.

The Nasrand intrusion، in the central part of Uromieh-Dokhtar magmatic belt is mainly composed of granite and granodiorite. The intrusive rocks are hosted by various dikes trending NW-SE. The granites and granodiorites are dominated by plagioclase، K-feldspar، quartz، biotite، amphibole، whereas the dikes are characterized b similar mineralogy in addition to pyroxene. The amphiboles are calcic with (Na+K) A≤0. 5 and magnesio -hornblende composition in the granitic rocks with (Na+K) A>0. 5 and AlIV3 are magnesio-biotites. The pyroxenes in the studied dikes are clinopyroxene with augite composition. The mineral chemistry of the biotites، amphiboles and pyroxenes indicate that this intrusion is calc-alkaline and have been crystallized in a subduction zone setting.

The Delbar metamorphic complex is located 130 km southeast of Shahrood (Biarjmand area) in the northern margin of the Central Iran. This complex consists of four groups include metapelitic، metapsammitic، metacarbonatic and metabasitic compositions. Field evidences indicate the protolith of the complex were shale and sandstone (psammite and graywacke) alternation with carbonate layers in the upper parts. The complex crosscut by numerous diabasic dikes with late Neoprotrozoic- early Cambrian age which evolved to the foliated metabasites such as amphibole schist، amphibolite and garnet amphibolite. The sedimentary sequence in which diabasic dikes intruded subjected by intermediate P-T regional metamorphism (Barrovian type). The results of thermometry based on the varied calibrations of garnet-biotite pair and barometry through GBPQ method demonstrate 468-498 ˚C and 6. 4-7. 2 Kbar for micaschists and 645-706 ˚C and 8. 4-13. 2 Kbar for gneisses indicating greenschist for micashists and upper amphibolite facies for gneisses respectively. The increase of temperature and pressure confirms the prograde regional metamorphism event up to acheive the melting point and the partial melting initiation. The diverse migmatite structures generated in the metapelitic and metapsamitic rocks from felsic meltsexposed as the anatectic granites and leucogranites. The results of U-Pb age dating indicate 541±4. 7 Ma to 547±9. 9 Ma (late Neoprotrozoic- early Cambrian) age range. The regional metamorphism event in the Delbar complex is related to the Pan-African orogeny according to the obtained age data and with comparsion to the other similar metamorphic complexes and granitoids in the Central Iran.

The east Nabar volcanic rocks with Eocene age are located in the southwest of Kashan and Uromieh-Dokhtar magmatic belt. These rocks are composed of basaltic andesite، andesite، dacite and rhyolite. Plagioclase، amphibole، clinopyroxene، biotite and quartz are the essential minerals of these rocks. Very few apatites are observed in some plagioclases. Epidote، calcite، chlorite، sphene and opaque are secondary minerals. Porphyritic، glomeroporphyric، microlitic and poikilitic textures are common textures in these rocks. On the base of microprobe analyses the composition of plagioclase ranges from oligoclase to labradorite، the clinopyroxenes are diopside and the amphiboles are magnesio-hornblende and tremolite. The chemistry of clinopyroxenes show that these rocks belong to sub-alkaline series and volcanic arcs. On the base of barometry of clinopyroxenes، the study rocks formed in medium to low pressure during their ascending. The volume of water in the crystallization environment of clinopyroxenes was high and the rocks studied formed in high oxygen fugacity. The thermometry of clinopyroxenes reveals the temperature of 975 oC for their crystallization. The amphiboles thermobarometry shows the pressure of 2. 97 kbar and the temperature of 700-750 oC.

The Mio-Pliocene volcanic rocks are exposed in the north and the northwest of Shahre-babak (Trishkuh، Miduk and Sara masses) Kerman province. These rocks formed a part of Uromieh-Dokhtar magmatic belt and consist of andesites and dacites. The rocks studied have porphyritic texture and Phenocrysts wiht plagioclase، sanidine، amphibole، biotite and quartz. Based on geochemical data and multielements pattern، these rocks are medium to high K calc-alkaline suite and show LILE and LREE enriched normalized multi-element patterns، and Nb and Ti deplated. Chondrite normalized REE patterns of the studied volcanic rocks display a decrease from LREE to HREE without any Eu anomaly and formed in subduction zone in an active continental margin. They have higher SiO2، Sr content، Sr/Y and La/Yb ratios and lower MgO، Y and Yb contents in compare to those of normal calc-alkaline volcanic rocks and show characteristics of HSA (high SiO2 adakites). HREE and Y depleted patterns suggest the existence of garnet and amphibole as a residue in the source. The source of these rocks was probably garnet-amphibolite possibly generated during subduction of the Neo-Tethyan oceanic slab beneath the Central Iran zone.

The Bezow-Daghi area is located in the west side of Urmia Lake and northeast of Urmia Town. In the area an individual volcanic dome is observed which is accompanied by different pyroclastic and volcanic products (acidic to intermediate composition) mainly dacite. The major minerals are plagioclase and amphibole set in the microlitic to hyaline matrix. Geochemical studies show that the rocks are dacite with high potassic calc-alkaline to shoshonitic affinity. LREE/HREE ratio is high (La N/Yb N≈20). Depletion in HREE، HFSE and TNT contrary to LILE and Sr enrichment and VAG setting are the significant features of these rocks. Detail investigations on the rocks studied confirmed that the dacites are HSA type adakite and its magma is generated as a result of partial melting of subducted slab (eclogite) and overlying sediments during post-collisional period. All geochemical characteristics reported for adakite، in the petrologic literatures، are well consistent with those of Bezow-Daghi adakites i. e. Sr>400 ppm، MgO<3%، Al2O3>15% and SiO2>56%، enrichment in LREE and LILE، depletion in HREE and Y and high ratio of La/Yb>20 and Sr/Y>40.

The studied area is located in the SE of Mianeh and north of Zanjan، and it is a part of Western Alborz- Azarbaijan structural zone. This area consists of volcanic rocks including rhyolite، rhyodacite، dacite and pumiceous tuff with Oligocene age and andesitic lithic tuff with Eocene age. Acidic volcanic rocks crop out in the form of domes، lava flows and tuffs. Perlites crop out in lower part of the rhyolitic- rhyodacitic domes. All acidic rocks have shoshonitic nature and classified as peraluminous rocks. These rocks are characterized by LREE- rich patterns with high LREE/HREE ratio and distinctive negative Eu anomaly. There are distinctive positive anomalies of Rb، Th and Pb on the spider diagrams which is related to continental crust role in genesis and evolution of the parent magma. On the tectonic setting discrimination diagrams، these rocks are plotted within the Post-COLG setting. The overal petrographic، petrologic and geochemical evidences demonstrate that during the final stages of the continental collision، the thickened sub- continental lithosphere in the Alborz was delaminated and replaced by hot asthenosphere mantle. Rapid upwelling of hot asthenosphere gave rise to the partial melting of asthenosphere which is produced the Oligocene basaltic rocks near the studied area. Emplacement of basaltic magma in the upper part of the continental crust led to the partial melting of the crust and generation of the parent magma of the acidic rocks. Acidic lavas cooled rapidly and formed the glassy rocks such as obsidian which changed to perlite in contact with meteoric and warm waters.

In structural subdivision of Iran، the Takht area is located in the north of Uromieh-Dokhtar magmatic belt. According to field observations and mineralogical characteristics، the granitoids of Takht consist of granodiorite، quartz-diorite and tonalite. Intrusion of granodiorite into the Cretaceous carbonates produced iron skarn with distinctive zonation. Skarn zonation towards carbonates، include epidote، oligist-quartz، garnet، pyrite، magnetite، crystalline limestone، and carbonate zones، respectively. This distinctive zonation of skarn makes it very attractive. Based on chemical composition of garnets، there is solid solution between grossular and andradite. In spider-diagrams there are depletion of Ti، P and Eu and enrichment of Rb، U and Th LILE enrichment and depletion of HFSE. On Rb/Y+Nb diagram the granitoids of the area are I-type volcanic arc، which can be related to subduction of Neotethys oceanic crust underneath Central zone of Iran.

Numerous granitic bodies have been injected into the Precambrian basement of Central Iran in Kuh-e-Sarhangi area. Microscopic investigations and mineral chemistry point to the existence of white mica، biotite and epidote as primary (magmatic) and secondary (alteration) or re-equilibrated types. The important mineralogical indicators such as the presence of two separate feldspars and the existence of spessartine-poor garnet and magmatic epidote indicate magma crystallization at relatively high depths. Whole rock and mineral geochemical evidences of these bodies show granitic composition، with calc-alkaline characteristics and weak per-aluminous nature. In discrimination diagrams، the studied granites are I-type belonging to volcanic arc. The spider diagrams pattern of these granites are resemble to the subduction zone magma. There is considerable compositional overlap of rare earth and trace elements patterns of Kuh-e-Sarhangi granites and continental active margin of southern Andes. Considering of continental active margin setting for Central Iran in upper Precambrian-lower Cambrian is the involvement of this micro continent setting in the northern edge of Gondwana and subduction of Prototethys oceanic basin underneath it. The existence of some anorogenic intrusion bodies with mineralogical and whole rock alkaline characteristics in this area is probably related to the extensional basins of back arc or the influence of deep lithospheric faults.