In order to identify the provenance of met sediments of the Shahindezh Metamorphic Complex (SMC), NW Iran, we have studied the bulk chemistry of the METAPELITES in the mentioned area. The geochemistry of these rocks suggests that the parent sedimentary rocks are classified as shale. Major and trace elements concentration (e.g. TiO2, K2O, Ni, Rb) indicates that the primary igneous rock was acidic (andesite to rhyodacite). The chemical index of alteration (CIA) show that the source rocks have undergone moderate to high degree of chemical weathering and plagioclase composition varies from andesine to oligoclase. Using major oxides elements, the continental active margin is considered for SMC METAPELITES source. In comparison with average upper continental crust, the SMC METAPELITES show strong negative Ca and Sr anomalies and slight depletion in Nb and Mn but moderate enrichment in Y, Ba, Al and transitional elements.The similarity in the trends of multi-elements diagrams for all studied samples shows that bulk chemistry factor was constant variant at the different mineral par agenesis appearance process. Based on the standard PT pseudo sections drown by scientists for average metapelitic composition, Ms+Bt+St and Ms+Bt+St+Ky par agenesis were in equilibrium at the PT conditions estimated, previously.

The whole rock chemistry of the Garmichay METAPELITES located in the north of Miyaneh, NW Iran, is investigated to reveal the provenance and metamorphic conditions of the rocks. Petrofabric observations have revealed the syn-tectonic nature of regional metamorphic cordierite porphyroblasts in the METAPELITES. C' shear band structure is another feature that is observed in the rocks. Two regional metamorphic phases (RMP1, RMP2), one contact metamorphic phase (CMP) and two deformation (D1, D2) phases are identified. The major oxide geochemistry implies two sedimentary shale and greywacke parent rocks. Based on major, rare earth and trace elements (Ti, Ni, TiO2, Zr and K2O) the igneous source rock has been an andesite to dacite/rhyodacite. The CIA (chemical index of alteration) and CIW (chemical index of weathering) parameters imply a medium degree of alteration in the igneous source area. The Garmichay METAPELITES, in comparison with the PAAS and UCC, are enriched in Cs, La and Ce and depleted in Sr, Nb and Ta. The representative samples lie inside the paragenetic triangles of the compatibility diagrams that imply their thermodynamically stable conditions. Finally, based on the standard pseudosections, the maximum temperature and pressure range has been determined as 535-635 ° C and 1-3 kb, respectively.

Intrusion of the Alvand complex (intrusions formed during Jurassic) into the host metapelitic rocks (schists) created pelitic hornfelses and anatectic migmatites in the Alvand aureole. Partial melting in the Alvand aureole was restricted to pelitic bulk compositions. Existing of spinel-quartz minerals and appearance of orthopyroxene in these rocks marks the transition from amphibolite- to granulite-facies conditions, and is commonly attributed to the process of fluid-absent partial melting. Reactions Sil/And + Bt = Crd + Spl+ Kfs + melt and Bt+Als+Pl+Qtz = Grt+Kfs+melt, are the most reactions for the development of melt in the metapelitic rocks of Alvand aureole. This metamorphism is mainly controlled by conductive heat transfer through magmatic intrusions into all levels of the crust. The Hamadan metamorphic rocks have experienced multiple episodes of metamorphism driven by burial and heating during arc construction and collision during subduction of a Neotethyan seaway and subsequent oblique collision of Afro-Arabia (Gondwana)with the Iranian microcontinent in the Jurassic-Cretaceous, and these events are associated with local partial melting at high grades, near the Alvand complex pluton.

Introduction The Sanandaj-Sirjan zone, one of the most critical areas for studying metamorphic events, originated by subduction of the Neotethys oceanic lithosphere beneath the Central Iranian microcontinent during Early Jurassic to Late Cretaceous (Berberian and King, 1981; Alavi, 1994; Hassanzadeh and Wernicke, 2016). The Qori metamorphic complex located in the southeastern part of the Sanandaj-Sirjan zone (Figure 1). Fazlnia et al. (2009), suggests a regional metamorphic phase (c.a. 187 to 180 Ma) concurrent with the orogeny activities, and another phase (c.a. 147 Ma) associated with arc magmatism. The main purpose of the present paper is to investigate the metamorphic evolution of Qori complex METAPELITES using the phase diagram calculations. This research can enhance the accuracy of previous studies and provide researchers with a better understanding of thermodynamic changes during progressive orogenic metamorphism related to the tectonic evolution of the southern Sanandaj-Sirjan zone. Geological setting The Qori metamorphic complex mainly comprises alternating actinolite schists, garnet amphibolites, and marbles interbedded with METAPELITES (garnet-kyanite-biotite schists) and metaultramafic rocks (olivine-orthopyroxene-spinel-hornblende schists) (Figure 2), subjected by Barrovian-type metamorphism (Fazlnia et al., 2009). The previous studies have reported peak metamorphic conditions of 9.2 ± 1.2 kbar and 705 ± 40°C attributed it to crustal thickening in the course of Early Cimmerian orogeny(180 - 187 Ma) (Fazlnia, 2007, 2017; Fazlnia et al., 2009). The rift propagating activity in Gondwana (Golonka, 2004; Sears et al., 2005) led to non-orogenic magmatism in northeastern Neyriz and the intrusion of the heterogeneous Talle-Pahlevani batholith into the semi-pelitic to pelitic metamorphic rocks of the Qori complex (Fazlnia et al., 2009). This caused intense contact metamorphism and migmatization at 700 to 750°C and P> 5 kbar (Fazlnia et al., 2023; Miri and Fazlnia, 2024). By the closure of the Neotethys, the study area underwent deformation, as the other parts of the Sanandaj-Sirjan zone. Material and methods About 50 metapelite samples we studied using polarizing microscope. The 6 selected samples were analyzed for their major oxides by a Philips PW1480 XRF instrument in University of Kiel, Germany. Petrography The major minerals include biotite, quartz, garnet, muscovite, kyanite, plagioclase, chlorite, staurolite, along with minor amount of magnetite, rutile and porphyro-lepidoblastic texture. Two foliation fabrics, S1 and S2, are traceable in the area (Figure 3a), leading to the preferred orientation of biotite and muscovite (Figure 3b). The main stage of the garnet and staurolite growth occurred during the second metamorphism stage along with S2 foliation. They were replaced by biotite, muscovite and chlorite through the retrograde metamorphism (Figures 3e, f). In higher P-T, the staurolite became unstable, and kyanite replaces it (Figure 3g) indicating the middle amphibolite facies condition (Bucher and Grapes, 2011). In the final stage of the metamorphic process and cooling, magnetite crystals formed post-tectonically, cutting through the rock foliation (Figure 3f). The lack of pressure shadows in these crystals point to  post-tectonic growth. Geochemistry The chemical data of the whole-rock are represented in Table 1. The samples plot between the pelitic and mafic rock fields on a discrimination diagram (Figure 4a), although, the presence of kyanite and staurolite reveals their metapelitic natures (Bucher and Grapes, 2011). The FeO/K2O versus SiO2/Al2O3 diagram (Figure 4b) suggests a Fe-rich sandstone for their protolith. Discussion Phase diagram modeling The sample Af-220, containing peak P-T mineral assemblage and sufficient Al2O3, FeO, and MgO contents to form the desired minerals, was selected for calculations. The calculations were performed using Theriak-Domino software (de Capitani and Petrakakis, 2010), version 10.0.19044.1526, released in 2018, with the tcdb55c2d database in a K2O-FeO-MgO-Al2O3-SiO2-H2O (KFMASH) chemical system (Figures 5 to 7). The fluid was considered as pure water and in-excess. The solid solution models used in calculations include GARNET (White et al., 2007) for garnet, CHLORITE (Holland et al., 1998) for chlorite, PHNG (Coggon and Holland, 2002) for muscovite, BIO (White et al., 2007) for biotite, CORD (Holland and Powell, 1998) for cordierite, and LIQtc (White et al., 2007) for melt. Metamorphism conditions The stability fields of garnet + biotite + kyanite + sillimanite indicating peak metamorphic condition occur at T 650 to 780°C and P >7 kbar (Figures 5, the blue dash-line). At higher T, melt appears, suggesting that the sample did not experienced T>780°C. It should be noted that there is no field containing the kyanite and the sillimanite as well, but their coexistence in the samples display the polymorphic transformation P-T condition. However, the occurrence of sillimanite in the samples under study point to the higher T than that of kyanite, the field 1 is considered as the peak metamorphic condition prior to anataxis. This thermal shock occurred due to intrusion of the Talle-Pahlevani pluton into Qori METAPELITES (e.g. Fazlnia et al., 2023). Cordierite appears at P<7 kbar, thus, its absence in the samples indicates a minimum P of 7 kbar. Influence of protolith composition A MgO/(MgO+FeO) vs. T phase diagram at 8 kbar P (Figure 6) shows that the peak assemblages occur at MgO/(MgO+FeO) ratios of 0.2 to 0.5. Also, an Al2O3 vs. T phase diagram (Figure 7) suggesting that the assemblage requires at least 10 wt% Al2O3 to form kyanite and sillimanite at peak condition. Conclusions The METAPELITES of Qori complex originated from a Fe-rich sandstone protolith; The parageneses include (1) chlorite + muscovite + biotite (greenschist facies) → (2) biotite + garnet + staurolite (lower amphibolite facies) → (3) biotite + garnet + staurolite + kyanite + sillimanite (medium to upper amphibolite facies); Thermodynamic phase diagram calculations indicate that the peak assemblages formed at 650 to 780 °C and 7 kbar; The MgO/FeO and Al2O3 contents of the protolith affected the peak mineral assemblage.

Pressure and temperature of metamorphism in the Mahneshan area were estimated in order to determine the type of metamorphism and tectonic setting of the rocks. Biotite, muscovite, plagioclase, garnet, quartz, andalusite and staurolite minerals are crystallized together in METAPELITES in the regional metamorphic rocks of southwest Mahneshan. Chemistry of coexisting minerals is studied using microprobe analysis. Using multiple equilibria calculations and THERMOCALC program, temperatures of ~520°C and pressure of ~3 kbar have been calculated for the formation of these rocks. Using these data, geothermal gradient of 60°C/km has been calculated for the upper crust of the Mahneshan. Based on calculated geothermal gradient, the Buchan type metamorphism is suggested for the metamorphic rocks of southwest Mahneshan.

The Gash metamorphic complex is situated at the west of Rasht city. Gasht-e-Rodkhan metamorphic rocks are considered as a part of this metamorphic complex. METAPELITES (schist, gneiss and migmatite) are the most important lithological unit of the Gasht-e-Rodkhan area. Index minerals consist of staurolite, garnet, sillimanite and kyanite. The main rock forming minerals of muscovite-free melanosome of migmatites are sillimanite and biotite. There is garnet in some melanosome as well. Quartz, K-feldspar and plagioclase are the rock forming minerals of leucosome. Tourmaline, garnet, muscovite and sillimanite are accessory minerals. Average pressure and temperature calculated by Thermocalc software and conventional thermobarometers for schist, gneiss and migmatite samples are 8. 6 Kb, 630° C; 6. 7 Kb, 650° C and 6. 3 Kb, 720° C respectively. Mineralogical parageneses and geothermal gradient resulted from thermobarometry calculations of the Gasht-e-Rodkhan METAPELITES are compatible with metamorphic Barrovian gradient or orogenic type. Gash complex probably represents metamorphic rocks of medium crustal depth of a collisional tectonic setting between Alborz block and Turan plate. Partial melting of METAPELITES and generation of associated leucogranites have taken place as a consequence of muscovite dehydration melting.

The METAPELITES of North of Golpayegan show that these rocks can be divided into four categories based on mineral assemblages: garnet- chloritoid- schist, garnet- schist, garnetstaurolite schist and staurolite- Kyanite- schist. The appearance of chloritoid in garnetchloritoid schists shows green schist facies. Garnets in garnet- schists shows 3 stage of growth. The appearance of staurolite in garnet- staurolite schists signifies the beginning of amphibolite facies. Petrological changes from garnet- chloritoid- schists to staurolite- Kyanite schists shows the formation of this rocks in a prograde metamorphism. The thermodynamic study of these rocks shows that North of Golpayegan's METAPELITES were formed within a temperature range of 480-560oC and a pressure range of 1.6-4.1 kbar. These results are consistent with the minerals' paragenetic evidence and show that effect of metamorphism on North of Golpayegan's pelitic sediments is to lower amphibolite facies (Epidote amphibolite).

Tanbour metamorphic complex east of Sirjan is compoused of metasediments and metabasic rocks. Petrofabric study of this complex shows two metamorphic and two deformational phases. Chemical studies of index minerals indicate that second phase of metamorphism occurred with a degree up to lower amphibolite facies. Mineral assemblage of first phase are biotite, muscovite and garnet while staurolite appears in peak of second phase of metamorphism. Mineral chemistry studies indicate that second phase of metamorphism occurred up to staurolite zone. Tempretures and pressures about 550-590°C and 7-8/48 kb were also estimated using geothermobarometry. The data suggest that these metamorphic rocks underwent a medium P metamorphic event.

Chloritoid as one of the common metamorphic mineral in low to medium grade METAPELITES, is absent in metapelitic rocks of Hamedan area. Comparing with geochemical limitations for Chloritoid appearance in METAPELITES, whole rock composition of the area is suitable for Chloritoid formation. Since P, T and X are in appropriate range for Chloritoid, the role of fluid could be important. Microscopic investigations show that all metapelitic rocks are in equilibrium with graphite and fluid composition is combination of CO2 and H2O. Based on estimated P and T, highest portion of H2O in the fluid, could be 0.9. Although this is highest approximation, it can conclude that for Chloritoid appearance, XH2O in fluid must be more than 0.9. Since in the Hamedan area staurolite is widespread and Chloritoid is absent - considering almost same composition between chloritoid and staurolite - the composition of fluid is more important. There are many doubts in geochemical limitations for Chloritoid appearance. Considering the results of this study and in the case of attention to fluid composition, geochemical limitations will change and Chloritoid could appear in many rocks, as its higher temperature equivalent, staurolite.

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.