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The Upper Devonian - Lower Carboniferous Sourian
complex, is composed of clastic - carbonates, volcanic, metamorphic
rocks and quartz lenses hosts copper mineralization in Gian area of
Fars province.
This complex is metamorphosed to green schist facies. This
metamorphism resulted In massIve to disseminated sulfide
mineralization in the direction of schistosity and within quartz lenses.
Low-grade green schist facies metamorphism is recognized with
cataclastic flow and fracturing of pyrite crystals, infilling of fractures
of pyrite with chalcopyrite, pressure shadow of chalcopyrite around
pyrite, recrystalization and presence of triple junctions in pyrite.
Distribution pattern of REE in schists of Gian copper shows a
decreasing trend from La to Lu. The ratio of 2:LREE/LHREE is more
than one and the ratio of LaN I YbN is less than 15. This indicates that
schists are formed by the metamorphism of shales and the ratio of
(LalLu),,> 1 indicates that the transfer of REE has been affected by
surface adsorption. It may be concluded that this copper occurrence is
the result of ore-bearing shale metamorphism.

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The quartz-aluminosilicate veins in the Hamadan region consist of quartz with one, two or three polymorphs of aluminum silicate )andalusite, kyanite and sillimanite(. In some veins other accessory minerals (i.e. garnet, chlorite, muscovite, staurolite, biotite and plagioclase) are present. The petrogenesis of these veins and their country rocks have been previously described; this paper studies oxygen isotope ratios of co-existing quartz and Al₂SiO₅ to determine formation conditions and genesis of these veins. The δ ¹⁸O/ ¹⁶O values of quartz, andalusite, kyanite and sillimanite range from: +(16.8-17.1)‰, +(14.2-14.5)‰, +14.1‰ and +14.6‰, respectively. These results indicate a possible metamorphic origin for fluids responsible for the formation of these veins and magmatic origin of fluids is unlikely. The estimate temperature for the formation of veins is about ~ 480-550 ^oC, a range thet consistent with petrographic observations in the veins and previous thermometry results on host rocks of veins.

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Intrusion of the Chahghand gabbrodiorite in regionally
metamorphosed rocks of the Sanandaj-Sirjan zone in NE of Neyriz has
caused contact metamorphism. A variety of pelitic hornfelses are formed as
a result of thermal metamorphism. Spatial distribution of minerals in the
Chahghand aureole defines three mineralogical zones namely cordierite,
andalusite and sillimanite zones. Study of metamorphic reactions and phase
relations indicate a pressure of 2.5 to 3.5 kbar and temperature of 500-600 oC
and ~700 oC for the andalusite and the sillimanite zones respectively. Apart
from crystallization of prismatic sillimanite in the sillimanite zone, fibrolite
is formed in the other zones. It seems that cation leaching and deformation
were the major processes in the formation of fibrolite in the Chahghand
aureole. Regarding appearance of fibrolite in altered rocks far from the
igneous contact, fibrolite is not crystallized within the sillimanite stability
field, but it may has crystallized at lower temperatures. Therefore
considering fibrolite in the rocks equivalent to sillimanite existence and
estimated pressure and temperature on this basis, at least the altered rocks
within the thermal aureoles is fraught with some problems.

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Metamorphic rocks of the Hamadan region have experienced
regional and also contact metamorphism (due to intrusion of gabbro, diorite
and granitic bodies), therefore, their mineral assemblages have formed in
multiple stages. Evidence of regional metamorphism (M) and contact
metamorphisms at the contact of gabbros (M’1) and porphyroid granites
(M’2) are separatable, hower At the contact of hololeucocratic granites a very
local contact metamorphism (M’3) have occurred (from a few decimeter up
to a few meters, due to small size of these bodies). Minerals such as micas,
garnet, staurolite, cordierite, andalusite, kyanite and sillimanite are usually
produced by several reactions, and participated in other reactions to form
other minerals. The relationship between mineral growth to deformational
events have been found at several stages (i.e. pre-tectonic, syn-tectonic and
post-tectonic minerals are common in metamorphic rocks of the region.)
Pegmatites and silicic veins have played essential role in some metamorphic
reactions as sources for heat and fluids, so that some metamorphic minerals
are common near these veins and disappear far from the veins. Considering
observed mineral assemblages in metamorphic rocks of the region, regional
metamorphism can be correlated with low to moderate P/high T Buchan type
metamorphism. In final stages of metamorphism, high T minerals such as
cordierite experienced retrograde reactions or pseudomorphed and higher
pressure minerals such as kyanite have been more stable.

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Mantle peridotites are one of the most important rock units of
Jandaq ophiolite that are affected by numerous,phases of dynamic and static
serpentinization, and metamorphism. The main part of mantle peridotites is
lherzolite. This ophiolitic association is covered by Paleozoic metamorphic
rocks that are schist and marble. All olivines are changed to serpentine. Most
of orthopyroxenes are bastitized and some of clinopyroxenes are changed to
tremolite by metamorphism. Clinopyroxenes are the most resistant mineral
against the metamorphism and alteration. Most of spinels are magnetitized,
but in some cases the inner parts are fresh. Composition of chromian-spinels
are the same in all mantle peridotites with CrN "" 0.46. Gabbros that intruded
the peridotites are rodingitized. Peridotites of Jandaq ophiolite are abyssal
peridotites that belong to spinel lherzolite facies. Crystallization temperature
of pyroxenes in Iherzolites ranges from 1041 to I 178 DC. One of the most
characteristics of these peridotites is absence of chromitite that relates to
lherzolitic system of mantle, low degree of partial melting, low activity of
mantle in continual ascending melt production, and low Cr content of
pyroxenes.

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On the basis of microstructural evidence it is clear that SMC metapelites have experienced at least two regional (RM1, RM2) and one contact metamorphism (CM). During RM2, several porphyroblasts including kyanite, andalusite, staurolite, cordierite, garnet and fibrous sillimanite have grown in the mica - schists. In order to estimate the PT condition of metamorphism of metapelites, we used cation exchange and multi-equilibrium methods. Temperature of RM2 estimated using, Grt - Bt and Grt - Chl thermometry 650 - 700 °C. Also PT conditions are calculated by THERMOCALC computer program which is based on multi-equilibrium reactions. Kyanite - staurolite - cordierite - bearing mica - schists are metamorphosed at pressure ~5 - 7 kbar and temperature ~650  ±50 °C. Thermal gradient at the SMC is considered to be ~ 40 °C/km. This thermal gradient is similar to those from continent-continent collision settings.

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The calcareous rocks in the Takht-e- Soleyman area (NW Iran) crop out in association with a variety of metamorphic rocks including amphibolites, granitic gneisses, pelitic schists and meta-ultramafic rocks. Retrogressive metamorphism of these rocks occurred during decompressional cooling during exhumation. Cummingtonite-bearing rocks resulted from retrogression of the calc-silicates in the area. Their dominant mineral assemblage is plagioclase + garnet + calcic – amphibole + ferromagnesian – amphibole + quartz + calcite ± titanite ± epidote. Calcic - and ferromagnesian - amphiboles were determined by petrographical observations and EMPA analysis. Hornblende and cummingtonite compositions dominate the analysed amphiboles. Formation of Ca-poor cummingtonite coexisting with calcite and calcic - hornblende in the retrograde calc - silicates of the Takht-e-Soleyman area is a rare petrological occurrence. Thermometric estimates using mineral compositions of cummingtonite co-existing with hornblende is in the range of 550 -600 ºC. Al in hornblende barometry yields a pressure of 6.5 ± 0.6 kbar, corresponding to medium pressure amphibolite facies.

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Eocene volcanic rocks in south of Asad Abad (north-east of Koohpayeh, Isfahan Province) experienced very low-grade metamorphism (hydrothermal metamorphism), resulting in prehnite, malachite, azurite, zeolite, quartz and calcite crystallization in cavities and fractures. Chlorite (brunsvigite) and amphibole (ferro-actinolite) appear on secondary phases. Augite and labradorite are two main minerals based on electron microprobe analyses and petrography evidence. Composition of minerals in these volcanic rocks and xenoliths are similar. Field and microscopic evidence show that an alternation of acidic and basic magmatism has occurred in the study area. Very low-grade metamorphic minerals formed in neutral to slightly alkaline PH, low CO₂, at temperature of 200-400^oC and pressure lower than 3 Kbars. Based on calculations, clinopyroxene and plagioclase phenocrysts in basaltstic magma in the study area have formed at temperature of 1100^oC and pressure of 3.17 Kbars corresponding to a depth of 11 Km. Chemistry of volcanic minerals and open space fillings minerals is close, both are rich in Ca, Si and Al and relatively poor in Fe, Na, K and Mn. This shows that the volcanites chemistry had important role in composition of metamorphic minerals. On the basis of the geochemical studies and tectonic setting patterns, these rocks are volcanic arc basalts. These basalts belong to the calc-alkaline magmatic series.

Keywords: Basalt, Eocene volcanism, Very low-grade metamorphism, Koohpayeh

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All samples of Shanderman eclogites contain amphibole. Epidote group minerals and chlorite formed during retrograde phases of metamorphism. Amphiboles show zoning with high FeO and Al₂O₃ content at the rims and high MgO in the cores in some samples. In these samples, the amphibole compositions vary from tremolitic hornblende to tschermakite and edenitic hornblende from core to rim, respectively. Amphibole inclusions in zoisite have similar composition to matrix amphiboles and show tremolitic hornblende nature. Epidotes include both zoisite and clinozoisite in all samples. They show zoning and have high Al₂O₃ content in the core and high FeO content at the rims. Pistasite content in the core is 0.09% and at the rim is 0.17%. Plagioclase is enriched in Na and is almost in the pure albite endmember. Chlorites are MgO rich and are of Repidolite and Brunsvigite types. They show FeMg_-1 and tschermakitic substitutions. Fe/Mg distribution coefficient among amphibole and chlorite for the cores of the minerals is around 0.5 and for the rims is 1. Thermobarometry of zoned amphiboles show that these minerals are grown from core to rim due to an increase in temperature and pressure. 

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The study area is located about 110 kilometers southeast of Mashhad and approximately 40 kilometers southeast of Fariman. The area is considered to be a part of the central Iran zone. It includes metamorphic rocks with different protoliths consisting of pelitic, carbonate and quartz - feldspathic rocks. The metamorphism in the study area is considered to be a contact regional metamorphism with a low pressure - high temperature grade. According to petrographic studies, the metamorphism in the region reached the upper limit of amphibolite facies.  On the basis of different mineral assemblages, three zones were recognized, including Andalusite-Cordierite, Sillimanite - Andalusite, and Sillimanite – K-Feldspar zones. Using Thermocalc software, the average temperature and pressure for the peak of metamorphism in the metapelitic rocks are 664 ºC and 2.5 Kbar respectively. Based on calculated maximum pressure (2.5 Kbar), the depth of ~7.8 Km for the metamorphism is estimated.

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The Sahebazzaman Mountain is located on the 8 km east of Kerman. In this area  a granitoidic body has intruded to the Cretaceous limestone and metamorphosed rocks. This skarns is covered with alluvial deposit also due to non enough erosion and existing of alluvial deposit, there is nonvisible but it has shown in isolated outcrop with 6 to 10 meter. The form of outcrop illustrat the granite intruded along the major fault with north-south trending. Petrography study show diorite to monzonite modal composition and skarns type is  exo-skarn calcitic. These rocks contain wollastonite, diopside, idocras, garnet, epidot ± cholorite ± calcite. Comparing Chemical composition between skarn and non-metamorphic limestone show, in addition to the heat energy, large amount of silicic fluid is responsible to this metasomatisme, therefore this is diffusion skarn. Metamorphic grad is about albite-epidote hornfels facies to pyroxene hornfels.

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Temperature and pressure of pelitic metamorphic rocks (metapelites), from the Jandaq area in NE Isfahan, are studied using pseudosection approach. The data used in this research are from already published data by other researchers; however the applied method is reported for the first time.  The metamorphism temperature is estimated to be about 400 to 670°C and pressure to be 2-6 kbar in the published study. Our study confirming these results, indicates the pressure and temperature more precisely. Also garnet and biotite chemical zoning is studied. Since garnet and biotite are the main ferromagnesian minerals in these rocks, the chemical zoning are determined for these two minerals, based on Fe and Mg content, and the P-T is estimated using Fe and Mg mole fraction in the minerals. Using the whole rock chemistry, the stability of the mineral phases is modeled considering metamorphic grade increase.

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Metamorphic rocks that mostly consist of amphibolite, amphibole schist, garnet hornblendite and rarely metamorphosed chemical and terrigenous sediments are found in the ophiolitic complex of north Torbat-E- Heidarieh. Thermobarometry calculations of amphibolite samples indicate temperature higher than 800 °C and pressure less than 5 Kb. Metamorphic conditions of  amphibole schist and garnet hornblendite samples such as pressure and temperature, range between 7.5 to 13 Kb and 570 to 770 °C. These metamorphic conditions are nearly compatible with the pressure and temperature calculated for the adjoining garnet schist. According to the amphibole chemical composition, textural and mineralogical evidences, thermobarometry calculations and the variations of metamorphic gradient, amphibolite samples have been considered as the product of hydrothermal system of mid ocean ridge. While the other samples are created owing to sole metamorphism during subduction initiation. The co-existence of metapelite with sole metabasites in the ophiolitic complex of north Torbat-E-Heidarieh confirming that the subduction process initiation and ophiolite emplacement took place has been in the vicinity of a continental margin.

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In Astaneh area (southwest Arak), in the contact with rhyodacitic subvolcanic rocks xenoliths with pyroxene- hornfels mineralogical composition have formed. These rocks have mineral paragenesis including corundum + spinel + andalusite + K-feldspar + plagioclase+ muscovite + biotite and chlorite with granoblastic, lpydoporphyroblastic, porphyrolpydoblastic, symplectite and poikiloblastic textures. In this complex, reaction texture (symplectite) of spinel + plagioclase+ muscovite, is replaced andalusite rim.  Petrography evidences show that the reaction texture of the andalusite rim has been created under conditions of partial melting. Geological and mineralogical evidence show that the pyrometamorphism process has been responsible as an indicator in this mineral complex. The field study, petrography evidence and thermobarometery (temperature 718 ^oC and pressure 2.8 kbar range) of these rocks show that the andalusite stability in the study xenolithe to the corundum-spinel zone is due to rapid incalescence rate of these rocks and overstepping. The heat diffusion from rhyodacitic subvolcanic is caused pyrimetamorphism process. So, the temperature period imposed and incalescence rate (geotherm gradient 60 ^oC/Km) on these xenoliths has been low and high, respectively.

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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.

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 Late Neoproterozoic (548-579 million years ago) metamorphic - igneous Shotor Kuh complex is cropped out in SE Shahrood, consist of a various range of rocks including metabasite, metapelite, metagraywake, metapsammite and metacarbonate. Metapelites include phyllite to gnessis and migmatite. Metamorphism intensity in the highest degree, progressed to anatexy and formation of granitic melts. Thermobarometery results  of metapelites can be correlated by the greenschist to amphibolite facies (T= 457-641 °C and P= 6-13 Kbar). According to the results, The primarily sedimentary sequences (prtolith of Shotor-Koh metamorphic - igneous complex) formed during intracontinental extensional- rifting regim in the sea- ocean basins. These sea- ocean basins, have been closed during Cadomian orogeny event, metamorphosed and consist of tectonic melange or accretionary prisms which thrusted on the neghibours continental crust.

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The Kermanshah ophiolite Complex is located in the structural – tectonic zone of the western Iran in northern part of Zagros main thrust and is a part of highly dismembered Kermanshah – Panjvin ophiolite belt. The poly metamorphic zone in this region is mainly related to the development and tectonic emplacement of the ophiolite. Some of the metamorphic rocks (Jade and its simulants) have so ​​hardness, density and high specific gravity, containing tremolite, actinolite, plagioclase, clinochlore, grossular and hydrogrossular garnet. Metamorphic rocks containing very condensed and compact tremolite and nephrite found in the area, as well as very compact antigoritic serpentinite so called bowenite, clearly proof that the high-pressure metamorphism took place during subduction. Serpentinites also appear in the region which is characterized by the predominance of antigorite and Cr-magnetite, as well as by their relatively low LOI (10.9-12.1 wt.%), corresponding to medium or high temperature blueschist facies metamorphism. These metamorphic conditions are strongly similar to the high-pressure metamorphic appearing in this serpentinites that formed from serpentinization of highly depleted harzburgitic protoliths where they were subjected to extensive partial melting processes (>15%), consistent with a hydrous subduction-related environment.  Gabbros in this ophiolite complex have been altered rodingitization, the altered rodingitized gabbros, in the continuation were underwent a de-rodingitization process too.

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The Almaghoulagh antiform in north of Asadabad, Hamedan, is one of the areas where the Paleozoic rocks are exposed in the Sanandaj-Sirjan zone. The antiform comprises two metamorphosed units. The Almaghoulagh unit in the lower part is overlain by the Chenar Sheikh unit, whereas the former derived from a volcanic protolith, the latter had a protolith with a significant sedimentary component. The Late Jurassic and Early Cretaceous felsic and mafic plutonic bodies are situated in the core of the antiform. The S1 foliation, which can be recognized throughout all the lithological units, is considered to formed during a regional metamorphic event. The amphibole-plagioclase thermometer and amphibole-garnet-plagioclase-quartz barometer yielded metamorphic temperature of 570°C and an average pressure of 7.2 kbar for the Almaghoulagh metabasites. The P-T condition of metamorphism in the Chenar sheikh metapelites was also estimated at 462° C and an average pressure of  2.6 kbar using the biotite-garnet thermometer and garnet-plagioclase-biotite-muscovite-quartz and garnet-plagioclase-muscovite-quartz barometers. These P-T estimations suggest that the regional metamorphism reached the amphibolite grade and the lower part of the Almaghoulah antiform experienced a higher degree of metamorphism.  The S2 foliation, which is the most penetrative structural element of all the rock units in the region, formed within a shear zone. Occurrence of the shear stress in the region, facilitated intrusion of the Late Jurassic and Early Cretaceous plutonic bodies into the core of the antiform. The emplacement of the plutonic bodies has played a major role in folding and doming the region.

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The studied area, as Ykeh-Chah unit, is a part of Golpayegan magmatic and metamorphic complex in Sanandaj-Sirjan structural zone. The unit consists of mylonitized and high- grade metamorphic rocks, including biotite-gneiss, biotite-garnet-gneiss, amphibolite and orthogneiss. The biotite gneiss and the biotite garnet gneiss have partly been migmatitized. They show various structures such as stromatic, ptygmatic, folded, ophthalmitic, net like, and patchy. Leucosomes are as in-situ and vein leucosomes. According to the leucosome type and some preserved igneous microstructures in leucosome, partial melting of metasedimentary units have been the dominant process in the generation of the migmatites. The most reliable microstructural criterion, as the evidences of partial melting in the migmatites, are simple twinning in K-feldspar, corroded biotite, plagioclase with zoning, melt presence, symplectic replacement aggregates in leucosome and mesosome, muscovitization some of the minerals. Due to the presence of leucosome and migmatization process, the rocks have been undergone the prograde metamorphism at the increasing temperatures until the partial melting, and finally experienced retrograde metamorphism during cooling. Evidence of the retrograde metamorphism in the rocks include the emplacement of rutile by titanite and ilmenite, symplectite texture (quartz + muscovite), myrmekite texture (quartz + plagioclase), atoll garnet, alteration of garnet to quartz and chlorite.

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This study focuses on the amount and concentration of trace elements and REEs pattern in garnet crystals which experienced regional metamorphism in the central Iran micro-continent, including the areas of Deh-Salm, Zaman Abad, Mishdowan, and Tanbour. Generally, garnet crystals are isolated from mica schists of greenschist to amphibolite facies. Mineralogical composition of garnets shows almandine rich in Mg and Mn. The REE pattern of garnets can be classified in two manners, one rich in HREE, and the other rich in LREE. The concentration and modification of the REEs of these minerals indicate the protolith enrichment and substitution of Y+HREE and HFSE with bivalent cations in their crystalline structure. Influx of concentrated trace elements and LREE fluids accounts for the enrichment of LREE and LILE in the second type, and it is the function of partition coefficients ratio between the minerals in equilibrium, crystallization and/or reaction with garnet crystal.