فهرست مطالب علی اصغر سپاهی

Pelitic schists containing high-pressure mineral assemblage were found from the Sanandaj-Sirjan metamorphic belt in northwest of Nahavand city in western Iran. Textural observation as well as chemical analyses of minerals shows that pelitic schists of the Nahavand area recorded two metamorphic stages. The earlier stage (M1) is testified by relicts of pyroxene, glaucophane and phengite inclusions in core of albitic plagioclase and winchite and phengite cores in chemically zoned amphibole and white mica, respectively. While the second stage (M2) is documented by tremolite, chlorite and muscovite in the main schistosity and in the pressure shadow of albitic plagioclase blasts. P-T estimation of M1 and M2 metamorphic stage by using calibrated thermobarometers and Thermocalc software revealed an average pressure and temperature of 15.5 kbar and 575 ◦C for the M1 stage, whereas the M2 stage has been constrained at P= 4.5 kbar and T= 600 ◦C. The obtained P-T pattern show a clockwise path in which the high-pressure metamorphic stage of M1 continued by the retrograde low-pressure metamorphic stage of M2. This P-T path could be formed during subduction of Neo-Tethys oceanic plate under Iranian plateau.

The Sarcheshmeh porphyry copper deposit (PCD) and other porphyry deposits occur in the the most important metallogenic belt in Iran, i.e. the Urumieh-Dokhtar magmatic belt (UDMB). The main phase of intrusion generation in various episodes of mineralization in the Sarcheshmeh area is a stock of granodiorite to tonalite (Shahabpour and Kramers, 1987) that is called the Sarcheshmeh porphyry. This stock intruded volcano-sedimentary rocks and alteration has centered on it. The oldest rock units of the area are Eocene volcanic rocks (Waterman and Hamilton, 1975), which are mainly andesites accompanying marine sedimentary rocks that is consistent with a submarine volcano-sedimentary basin environment. Granodiorite and quartz eye porphyry crop out in the northern part of the Sarcheshmeh PCD. The main objective of this study is to investigate their petrology and geotectonic environment.

Forty samples from drill cores and surface samples from granodiorite and quartz eye porphyry were collected. Twelve samples were chosen with the lowest degree of alteration (less than 5% of representative samples and low LOI) from amongst them for lithogeochemical analyses by ICP-OES and ICP-MS. Lithogeochemical analysis of the main elements was carried out using ICP-OES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) by lithiumborate fusion, and elemental analysis of trace and rare earth elements was performed by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) using sodium peroxide fusion in the SGS Company, Toronto, Canada.

Based on the Na2O+K2O versus SiO2 values on Cox et al. (1979) and Middlemost (1985) diagram, also R1-R2 diagram of De la Roche et al. (1980), the samples were plotted in the field of granodiorite and quartz diorite. On Harker diagrams, the contents of FeOt, CaO, p < sub>2O5, Al2O3, MgO, and TiO2 versus SiO2 show a decreasing pattern. Decreasing amounts of MgO and TiO2 can be related to early crystallization of ferromagnesian minerals and of CaO, Al2O3, and p < sub>2O5 to plagioclase and apatite crystallization, respectively. The chemical relationship and continuous pattern of the samples indicate that they probably resulted from fractionation of a unique magma. On the basis of the AFM diagram, they have calc-alkaline affinities. These observations and the presence of magnetite and other opaque minerals indicate high ƒO2 crystallization throughout fractionation stages. The samples of the study area were plotted in the calc-alkalic and alkali-calcic fields on a Frost et al. (2001) diagram and indicate that they are mainly magnesia consistent with oxidized I-type magmas.The spider-diagrams show negative anomalies in HFSE (especially Ti and Nb) and positive anomalies in LILE (especially in Ba and Rb). Negative anomalies of HFSE such as Ti, Nb, P and Ta can be related to the subduction of the Arabian plate under Central Iran and reflect the chemistry of the origin and crystallization-melting processes during evolution of the rocks. Moreover, it can be concluded that these elements remained in the source during partial melting, which is characteristics of I-type arc-related magmas. The behavior of LILE can be attributed to the behavior of fluid phases that were involved during the subduction. The REE diagrams show enrichment of LREE relative to HREE which can also be attributed to the subduction of the Arabian plate under Central Iran. Shafiei et al. (2009) and Asadi, 2018 proposed post-collision environment for the PCDs of the UDMB, especially in the Kerman part.By studying on the Dehaj-Sarduieh belt, Dargahi et al. (2010) concluded that the time of collision of the Arabian plate and the Central Iran continental plate was Late Eocene, and the Sarcheshmeh porphyry stock emplaced in post-orogenic environment like other stock porphyries of the UDMB. The samples of the Sarcheshmeh PCD plot in the mature arc area based on Rb vs Y+Nb diagram and it can be envisaged that they are related to the post-collision magmatic arc.

A metamorphic rock complex consists of slate, phyllite, micaschist and marble with NE – SW shistosity has cropped out in Neybaghi area in the NE of Myaneh.  Impure marbles occur as thick and thin layers or massive bodies within the centeral area of this complex. Textural and mineralogical evidences, revealed two metamorphic stages.  The early stage is testified by the minerals such as pyroxene (diopside), epidote (clinozoisite), amphibole 1 (edenite-pargasite) and plagioclase 1.  The main stage have chlorite (clinochlore), phlogopite, amphibole 2 (tremolite) and plagioclase 2.  P-T-XCO2 have been estimated for the early and main stage of metamorphism by computing nonideal and asymmetrical fugacity and activity and programing in THERMOCALC software for fluid and solid phases.  The estimations give pressure, temperature and XCO2 of 9.5Kbar, 660°C and 0.35, whereas the main stage has been constrained at P=4.2Kbar, T=510°C, XCO2=0.4. The obtained P-T path shows that the Neybaghi marbles were formed under medium pressure condition and overprinted by a low pressure metamorphism.  This type of P-T trend can be formed in collisional tectonic regime.

The intrusive body of the Shahrak is located between the West Azarbaijan and Kurdistan provinces. Lithologically, this intrusive body consists of granodiorite, monzonite, monzodoirite and monzogobbro, which intruded into Oligo-Miocene sedimentary units and Cretaceous and Precambrian metamorphic rocks. Mineral chemistry studies of granodiorite and monzogabbro rocks show that plagioclases have labradorite to bytownite composition, and clinopyroxenes are augite. Thermobarometry calculations of pyroxene minerals indicate that the formation temperature of these minerals ranges between  900 to 1250 oC  and the crystallization pressure of clinopyroxenes is estimated to be about 6 to 10 kbar. The geochemical investigations of the whole rock indicate that the magma has metaluminous and calc-alkaline affinity. In the multi-element spider diagram normalized to condrite and primitive mantle, there is a significant enrichment of LREE than HREE and depletion of Ti, P, Ta and Nb, which is a characteristic feature of the volcanic arc rocks of the subduction zones. Also, based on different tectonomagmatic diagrams, these rocks are located in the active continental margin environment. Based on REE elements, the parental magma of the studied rocks is probably originated from an enriched mantle.

Metamorphic area, which is a subject of this study, is located in S-Qorveh (Zarineh region), northwest of the Sanadaj-Sirjan zone. According to the recent dating, the S-Qorveh plutonic body consists of a complex of granitoids, granodiorites, quartz monzonites, and gabbros, have intruded into the host metamorphic rocks, about 149-152 Ma and have generated contact metamorphism. Intrusions of various masses and protolites, such as politic and basic layers, have made metamorphic rocks of this area to be different. Regional metamorphic rocks include slates, schists, and amphibolites which are metamorphosed in the range of middle green schists to the early amphibolites facies. Contact metamorphic rocks include spotted slates, mica hornfels, and cordierite hornfels which have been subject to metamorphism from albite-epidote hornfels to hornblende- hornfels facies. In cordierite hornfelses facis, by getting far from the intrusion, cordierite crystals become smaller in size and larger in number. According to the petrographic evidence, metamorphic rocks of this area have been subject to 3 phases of metamorphisms including probably high pressure regional metamorphism, regional metamorphism, and medium contact metamorphism. To estimate the metamorphism pressure-temperature state of this zone, TERMOCALC computer software and also linear calibrations have been used. Pressure-temperature calculations for regional metamorphic M1, have shown 3.9 Kbar pressure and 539°C temperature. For contact metamorphism M2, by using the software, average pressure of 4.3 Kbar and average temperature of 607°C have been calculated. Also, for the contact metamorphism M2, using the experimental calibration of biotite-muscovite equilibrium, the temperature estimated to be 581.3°C and using chlorite-muscovite equilibrium for this phase (stage) of metamorphism, pressure and temperature have been yielded 3.65Kbar and 620°C, respectively. In generally, results of temperatures for all metamorphic rocks are acceptable and satisfactory, but in contact metamorphic rocks, data of pressure may be higher due to emplacement of the granitoid intrusive body.

A wide range of plutonic rocks, ranging from mafic to felsic compositions, including various gabbros, diorites, tonalites, granodiorites, monzogranites, syenogranites and leucocratic granitoids, occur in the Alvand plutonic complex, Sanandaj-Sirjan zone, Iran. Age of this complex is middle Jurassic. In this complex, granitic and dioritic rocks occur as major constituents. Granites contain plagioclase, K-feldspar, quartz and bitite and diorites comprise plagioclase, hornblende, biotite and minor titanite and apatite. In some outcrops, contaminated granites and diorites occur which contain abundant large undigested xenocrysts of andalusite (partly to wholly converted to sillimanite) with spinel-rich and feldspathic reaction rims around them. These xenocrysts resulted from disintegration of minerals from pelitic rocks and their incorporation into host magmas. The 87Sr/86Sr isotope ratios in the studied granitic rocks vary from 0.7101 to 0.7245 and in the contaminated diorites from 0.7084 to 0.7079 (Sri more than 0.704). The range of 143Nd/144Nd ratios in granitic rocks is from 0.51234 to 0.51240 and for contaminated diorites from 0.51244 to 0.51252.The εNd(t) values for the studied granites vary from -3.2 to -3.98 and for contaminated dioritic rocks from -0.78 to -2.35.  In the 143Nd/144Nd versus 87Sr/86Sr diagram, granites plot in the field of crustal rocks; also diorites with mantle origin, in response to contamination by meta-pelitic rocks, are shifted towards rocks with crustal origin. These results indicate the importance of recognizing contamination of plutonic rocks by upper crustal (meta-pelitic) material when interpreting petrogenesis of such rocks.

The study area is located in west of Iran (38 km SW of Qorveh). This region is part of Sanandaj-Sirjan zone. This area contains several pegmatitic dikes and based on mineralogical and geochemical characteristics belong to muscovite-rare-element pegmatites. The lithology of this body varies from pegmatitic syenogranite to granodiorite. Various rock bodies in this suite are mostly I-type and calc-alkaline, with moderate to high K and regarding to the aluminum saturation degree they are subaluminous to peraluminous. The low (La/Yb) N ratio in the pegmatitic samples (2.28) indicates progression of fractional crystallization in the initial magma. The low Eu/Eu* ratio (0.137) in these pegmatites indicates differentiation of calcic plagioclase before pegmatitic stage. In the spider diagrams, LILE elements such as K, Rb and Th are enriched relative to HFSE elements specially Nb and Ti. Intrusion of this pegmatite in the carbonate rocks led to skarn development. These skarns have different minerals such as tremolite, epidote, scapolite, clinozoisite, pyrrhotite, pyrite, chalcopyrite and magnetite. Based on geochemical characteristics of these pegmatites, their composition, in accordance with bodies, is related to Sn, W and Mo skarns. This fact is in agreement with the studies in area regarding Sn & W mineralization.

Intrusion of the Alvand plutonic complex into the pelitic and sim-pelitic rocks of the Tuyserkan area has caused the development of a thermal aureole in the Sarabi area. The rocks within the aureole are thermally metamorphosed and formed different types of hornfelses. High-grade metamorphic rocks with chemically suitable compositions were melted adjacent to the contact due to the heat from the pluton. Heat derived migmatization in high-grade metamorphic and adjacent to the contact is observable. Scale of partial melting and volume of produced melt are very small. Main minerals in the light colored parts of the migmatites (leucosomes) include quartz and K-feldspar with an igneous texture specially euhedral to subhedral texture of K-feldspar, in which interstitial – textured – quartz filled their interspaces, Textural differences between light leucosomes and dark melanosomes, mineralogical composition of the leucosomes, existence of igneous textures within the leucosomes and restriction of the leucosome formation to the pelitic rocks all are distinct evidence for occurrence of partial melting in the Sarabi area aureole. The liable reactions for melting include fluid-present reactions and fluid-absent reactions. High-grade metamorphic assemblages contain corderite, sillimanite and garnet. Mineralogical compositions of leucosomes resemble leucogranites resulting from partial melting. This indicates crystallization of the leucosomes from a silicate melt.

The Alvand intrusive complex is located in south of Hamedan in Sanandaj-Sirjan Zone. This complex is composed of mafic to felsic rocks such as gabbro, diorite, tonalite, granodiorite, granite, aplite and pegmatite. Granitoid rocks comprise major part of the complex. Granitoids can be divided into two categories: porphyroid granitoids and hololeucocratic granitoids. Porphyroid granitoids are K-rich but hololeucocratic granitoids are K- poor. Petrographical and geochemical properties of granitoid rocks are seperate and they are not produced from a unique magma sources. Hololeucocratic granitoids in contrast to porphyroid granitoids are rich in CaO, Na2O and Al2O3 and poor in K2O, FeO and MgO. They are not producted from fractional crystallization of other granitoids. ΣREE and (La/Yb)N in hololeucocratic granitoids have wide range than other rocks. Eu/Eu* ratios in Porphyroid granitoids is 0.38-0.61 in hololeucocratic granitoids is 0.52-11.31 and in aplites is 0.15-2.15.  Porphyroid granitoids show negative Eu anomaly according to their crustal source. Considering that hololeucocratic granitoids are rich in Na2O and CaO, they are plagioclase rich and hence show positive Eu anomaly related to replacement of Ca by Eu in this mineral. Aplites and pegmatites of the region have characteristics resemble to porphyroid granitoids and are probably generated by differentiation of them.

The study area is a part of the Sanandaj-Sirjan metamorphic belt comprising regional and contact metamorphic rocks. The injection of the Alvand Batholith and intrusive body of the South West Malayer (South of Tuyserkan) into pelitic host rock has produced contact metamorphic rocks in the area. Metamorphic sequence is composed of slate, phyllite, schist, spotted schist, cordierite- bearing hornfels, metavolcanic, marble and metacalc– silicate. Pelitic rocks are the most abundant type of rocks. Regional metamorphic zones contain chlorite, chloritoid- chlorite, biotite and garnet zones and contact metamorphic zones contain cordierite, cordierite- andalusite, cordierite- k-feldspar± fibrolite zones.In fact, evidence suggests that following regional metamorphism, this area has been affected by intrusive bodies and contact metamorphism has been occurred. This zones show increase in metamorphic grade towards intrusive bodies. Field, microscopic and geochemical evidences show that the protolith of metamorphic rocks in the study area contain shales and siltstones with the interlayers of sandstones, intermediate- basic volcanic rocks and limestones.

The study area is a part of so-called Sanandaj-Sirjan zone or Zagros imbricate zone of the Zagros Orogen, Iran. The Hamedan region comprises a metamorphic sequence of low- to high-grade regional and contact metamorphic rocks intruded by mafic, intermediate and felsic plutonic bodies. The sequence comprises pelitic, psammitic, mafic, calc-pelitic and calc-silicate rocks.  Pelitic rocks are the most abundant rocks in the region which are mostly composed of slates, phyllites, mica schists, garnet-mica schists, garnet-andalusite-(±sillimanite/±kyanite) schists, garnet-staurolite schists, mica hornfelses, garnet hornfelses, garnet-andalusite-(± fibrolite) hornfelses, cordierite-(±andalusite) hornfelses, cordierite-K-feldspar hornfelses and sillimanite-K-feldspar hornfelses. Several interlayers of amphibolites and amphibole schists alternate with pelitic rocks in the sequence. Various types of Al2SiO5-bearing silicic veins occur in the region.  Isotope characteristics indicate metamorphic origin for some of them.  In this study, we have defined three different generations of kyanite according to their various geological characteristics, including: (1) metamorphic (randomly distributed and commonly co-existed with sillimanite/andalusite), (2) stress-(shear)-induced (pseudomorphs of kyanite after andalusite in the shear zones) and (3) late-stage (hydrothermal or metasomatic) kyanites.  The quartz-kyanite veins/pods are late structures that are created by interactions with wall rocks. Circulating Al- and Si-rich fluids may be responsible for formation of these veins/pods.