PETROLOGY
Year:2016 | Volume:6 | Issue:24|Papers Count:10

Volcanic and volcaniclastic rocks with Cenozoic age are widespread at Bozghush Mountain, south of Sarab, northwest of Iran. The composition of the studied rocks is trachybasalts, trachyandesites and megaporphyritic andesites with probable middle Eocene age (?). The main texture of these rocks is porphyritic. Plagioclase, clino-pyroxene and sanidine are the main minerals in these volcanic rocks. All volcanic sequences show similar trace element and REE patterns, with troughs in Nb, Zr, strong enrichments in Rb, Ba, Th, La and depletions in Ti, Yb, Y, relative to N-MORB, indicating a subduction-metasomatized lithospheric mantle as their melt source. On the basis of Sm/La versus Th/La diagram and Ba/Nb (>49) and Ba/Ta (>900) ratios, the influence of slab-derived sediments and fluids on the genesis of these rocks is obvious. It seems that the lithospheric mantle source beneath the Bozghush Mountain was metasomatized by subducted NeoTethys oceanic lithosphere derived fluids and subsequent slab break, delamination of the mantle lithosphere and tectonic extension due to the roll-back of the subducting Tethyan lithosphere which gave rise to decompression melting of the subduction-metasomatized lithospheric mantle and the generation of the studied rocks at Bozghush Mountain.

The Garmab Cu mineralization, in the east of Semnan and southeast of Shahroud, is situated in the Eocene conglomerate association with weakly hydrothermal altered. The weak alteration, mineralization and geochemical haloes is locally controlled by faults and late fractures. At the surface, secondary copper minerals including malachite and azurite and in the depth, primary sulfides generally are pyrite, arsenopyrite and chalcopyrite. Gangue minerals of the veins are commonly quartz, chalcedony, opal and minor calcite. Other components contain goethite, limonite and hematite with manganese oxides and minor jarosite smithsonite and gypsum. The results of statistical geochemical analyses indicate a positive correlation between copper with Au, Ag and As. According to host rock, mineralization, spatial relationships and geochemical dispersion patterns, deep drilling is suggested in the depth in the east of mineralization. The study district is related to buried intrusive bodies and epithermal vein-type Cu deposits.

The Gazestan iron oxide-apatite deposit, is locted 78 km east of Bafq at the Posht-e- Badam- Bafq block. Different kinds of lower Cambrian volcanic and subvolcanic rocks ranging from basic to felsic, outcrop in Gazestan area. Felsic volcanic rocks mainly are associated with orogenic phase and considered as an arc magmatism. In Gazestan deposit, host rocks display extensive alteration that can be classified into six groups including Sodic-calcic, potassic, sericitic, carbonates, silicic, chlorite ± actinolite ± epidote and tourmaline alterations. Chlorite ± actinolite ± epidote alteration is well developed throughout the Gazestan deposit.The ore body is mainly magnetite-apatite with less sulfides (Pyrite-Chalcopyrite) and REE minerals (allanite-monazite) which occur as breccia, banded, massive, stockwork and vein in altered volcanic rocks. Three generations of apatite are recognized which the second generation is usually enriched in REE minerals (monazite). The homogenization temperature of apatite (III) was calculated between 130-200 °C. The REE pattern of apatites show strong LREE enrichment with negative Eu and HREE anomaly. Magmatic fluids with high amounts of P, Fe and REE are responsible for the ore formation at the first stages. At the final stage of mineralization, meteoric (marine) waters mixed with the magmatic fluids, causing decrease in temperature and precipitation of late apatite and gangue minerals (calcite and quartz). The Gazestan deposit share many similarities with the Kiruna-type deposits (one of the subgroup of IOCG deposits).

An association of olivine-gabbroic dikes is located in the northwest of Iran, south-southwest of Germi city (Ardebil province), with N-S trend in the Talesh zone. Mineralogically, these rocks consists of phenocrysts of plagioclase, clinopyroxene (augite) and olivine with minor minerals of biotite, amphibole, apatite, opaque and zircon. The dominant textures in these rocks are porphyry, granular and ophitic. From the chemical aspect, the parent magma is alkaline nature. The spider diagram with a positive lead anomaly indicates the crustal assimilation process with LREE enrichment compared to HREE which is related to enriched mantle. The trend of major oxides vs. SiO2 on Harker diagrams indicates evolution process through differentiation, with slight metasomatism which can be related to subducted slab derived fluid. Based on the aforementioned evidences, the olivine gabbros were formed from an extensional back arc basin resulting from subducting oceanic crust in the northern branch of NeoTethys located between the blocks of Toriid-Anatolli in the south of Armenia beneath the crust of Quafqaz and Armenia.

Abstract 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 eNd values -4.18 to -4.72, whereas I-type granites have a much wider range in eNd of -0.8 to -4.3 and lower (87Sr/86Sr)i of 0.704867 to 0.708046. Initial eNd values for leucogranites range from +0.98 to +1.25. 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 study area is located about 30 km northwest of Maragheh in East Azerbaijan. The lamprophyric dyke intruded the Shemshak sedimentary rocks. Based on stratigraphic evidences, the age of dyke is probably Early Cimmerian. The principal minerals of the lamprophyric dyke consist of plagioclase (andesine -oligoclase), biotite (eastonite), phlogopite, olivine and clinopyroxene (diopside) with ocellar texture. The average chemical composition of clinopyroxene and plagioclase is En42.3, Wo46, Fs11.7 and Ab51.74, An30.92, Or17.34 respectively. According to the mineralogical and geochemical evidences, the studied lamprophyre samples are kersantite belonging to calc-alkaline lamprophyre.The plotted spider diagrams for the rock samples indicate the light rare-earth elements (LREE) and incompatible elements enrichment compared to heavy rare earth elements (HREE). The parent magma is probably generated from garnet lherzolite mantle with low rate partial melting. The studied lamprophyre dyke formed in intraplate and post collision environment which translocated possibly in basins and ruptures in related with fault systems.

The Vanako gabbroic body, southwest of Sahneh, extended along the Zagros ophiolite belt, in the west of Iran. The body contains plagioclase and pyroxene with minor amount of olivine and compositionally lie in the gabbro and olivine-bearing gabbro fields. Based on microprobe analyses, plagioclase composition is labradorite with An60.31-67.53 which has crystallized in temperature of about 950oC and low pressure. The composition of pyroxene is diopside and it has developed in medium to low pressure and temperature ranging from 800-1120oC. The low values of Fe3+ in pyroxenes and moderate values of An in the plagioclases point to the low fO2 in the composition of the parent magm. Also, the high values of Al2O3 in the pyroxenes and rare earth elements pattern normalized with chondrite infer that these rocks have been generated from fractionation of MORB type magma. The geodynamics situation of the Kermanshah area and the tendency of some samples to calc-alkaline affinity are further evidence to support a supra-subduction zone for the origin of these rocks rather than Mid-Oceanic Ridge basin.

Subvolcanic masses of Shah khairollah and Madvar located in the southeast of Urumieh-Dokhtar magmatic belt and northwest of Dehaj-Sardoieh belt, north and southeast of Shahr-e Babak city. Generally, these subvolcanic masses contain dacite, rhyodacite and rhyolite lavas. Mineralogically, they consist of plagioclase, amphibole, alkali feldspar, biotite and quartz and the dominant texture of the studied rocks are porphyritic. Based on Microscopic studies plagioclases show resorption and zoning and opaticitization is observed in the mafic minerals. Geochemical investigations show that the Madvar and the Shah khairollah masses are acidic in composition and all the rock samples fall in the field of calc-alkaline magmatic series, originated in an active continental margin arc setting. Chemical compositions of the studied rocks in spider diagrams show the significant enrichment in LREE rather than HREE, as well as Sr, K. The depletion of Pb, P, Pr, Zr, Y, Nb and Ti in those rocks are observed. The negative anomalies of Ta, Nb and Ti in the rocks studied is similar to those of the subducted rocks series. The values of MgO, Na2O, Ni, Cr and Mg#, depletion of Y and high ratios of LREE/HREE, Sr/Y (Ave. 137.26), La/Yb (Ave. 50) in the studied rocks are similar to those of adakites which have derived from partial melting of young oceanic crust. Geochemical characteristics of these two masses indicate the partial melting of oceanic crust prior to hydration and the low concentrations of Yb, Y, HREE, TiO2, is consistent with the partial melting of subducted oceanic crust slab under amphibolite facies conditions in the depth of 35 km.

The Kolah Ghazi granitoid body is located in the south-southeast of Isfahan and lies in the Sanandaj-Sirjan zone. The pluton is predominately composed of monzogranite, granodiorite and syenogranite. Quartz, plagioclase, K-feldspar, biotite, tourmaline, cordierite andalusite, sillimanite, kyanite, spinel and garnet are major and minor minerals of the pluton. The presence of kyanite in granodiorite enclaves may be due to melting of the pelitic rocks of the area which gave rise to formation of alumina rich restite. The occurrence of sillimanite these granitoid rocks can be related to metasomatism process. The inclusion of biotite and sillimanite needles in the cordierite indicates that the alteration of these minerals, during congruent melting, is responsible for the origin of cordierite. Further, cordierite crystallized during anatexis conditions under 660-770oC and 3.5 kbar condition. Growth of spinel around the aluminosilicates with symplectites texture represents conditions of high temperature, low content of SiO2, high fO2 in the Fe-enriched meta-argillite. The assemblages of cordierite, sillimanite, biotite and tourmaline with unusual common blue pleochroism in the Kolah Ghazi granitoids indicate the breakdown of tourmaline under temperature higher than 750oC. The origin of the garnet with almandine component in the Kolah Ghazi granitoids is magmatic source and refers to the pressure of 4 to 5 kbar, corresponding to depth of more than 18 km and temperature less than 850oC. As it may be observed from the mineralogical relationship, geochemistry of feldspar and Zr vs. SiO2 the pluton developed under 700-900oC and over 2 kbar PH2O.

The Iju porphyry stock as a part of the Urumieh-Dokhtar magmatic belt is situated 72 km northwest of Shahr-e Babak city and 147 km west-northwest of Sarcheshmeh porphyry copper deposit. The stock, intruded as a hybabyssal Miocene granitoid (9.25±0.5 Ma) the Eocene volcanic-volcanoclastic rocks and induced mineralization and alteration in the region. The existing phenocrysts in the Iju intrusive rocks including tonalite and quartz diorite with plagioclase, alkali feldspar, biotite and hornblende, which reside in a groundmass consisting of quartz and minor potassium feldspar and secondary minerals. The dominant texture in the rocks is porphyry. Based on petrography and geochemical analyses, the tonalitic rocks in the Iju region are classified as calc-alkaline and arc-related continental margin magmatism. High ratios of Ba/Nb (average 101 ppm) and Ba/Ta (average 1326 ppm) as well as the distribution of mantle-normalized trace elements (enrichment in LREE and LILE relative to HREE and HFSE, negative anomalies in Nb and Ta) indicate formation of the Iju granitoid is related to subduction. Evaluation of geochemical evidence including the amounts of SiO2>56%, Al2O3>15%, MgO<3%, Na2O>3%, Sr>300 ppm, Y<18 ppm, Yb<1.8 ppm, Sr/Yb>20, La/Yb>20, high enrichment in LREE and low enrichment in HREE show that the parent magma of the Iju tonalite has high silica adakitic affinity. The lack of negative anomalies in Eu and Ba in the rock samples point to the lack of influence of partial melting in the lower crust for this unit formation. Thus, the adakitic magma developed as the result of melting of subducting oceanic crust in the mantle and at the final stages of subduction or post-subduction.