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Major mineralogical and structural types of migmatites in the Hamedan region: a – sillimanite-migmatite and b – cordierite-migma- tite; c – stromatic structure; d – schollen structure; e – diktyonitic structure; f—h – progressive stages of partial melting in a pelitic-psam- mitic rock sequence from low degree (f – containing less melted and nearly undisturbed psammitic beds), to higher degree (g—h – containing disturbed and partially melted psammitic beds (shown by arrows); partial melting occurs around some of the Al 2 SiO 5 porphyroblasts (g)).
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Migmatites with evidence for low pressure metamorphism and partial
melting occur adjacent to the Alvand Plutonic Complex in the Hamedan
region of Iran. They show stromatic, schollen, diktyonitic and massive
structure. Sillimanite/andalusite/(kyanite)-garnet- and
cordierite-K-feldspar-andalusite-spinel-bearing migmatites are the most
common rock typ...
Contexts in source publication
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... migmatite types are present, namely Al 2 SiO 5 -bearing and cordierite-(± andalusite)-bearing migmatites ( Fig. 3a-b). Several structural varieties from stromatic to schollen, diktyon- itic, nebulitic and massive can be seen in many localities ( Fig. 3c-e). The progressive stages of partial melting can be ob- served in the outcrops (Fig. 3f-h). Metatexites show stromatic fabric with leucosomes commonly concordant to bedding planes, except in high ...
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... migmatite types are present, namely Al 2 SiO 5 -bearing and cordierite-(± andalusite)-bearing migmatites ( Fig. 3a-b). Several structural varieties from stromatic to schollen, diktyon- itic, nebulitic and massive can be seen in many localities ( Fig. 3c-e). The progressive stages of partial melting can be ob- served in the outcrops (Fig. 3f-h). Metatexites show stromatic fabric with leucosomes commonly concordant to bedding planes, except in high strain zones, such as faults and shear zones. The foliation-parallel leucosomes are usually 5-20 mm thick. The distribution of most of the ...
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... migmatite types are present, namely Al 2 SiO 5 -bearing and cordierite-(± andalusite)-bearing migmatites ( Fig. 3a-b). Several structural varieties from stromatic to schollen, diktyon- itic, nebulitic and massive can be seen in many localities ( Fig. 3c-e). The progressive stages of partial melting can be ob- served in the outcrops (Fig. 3f-h). Metatexites show stromatic fabric with leucosomes commonly concordant to bedding planes, except in high strain zones, such as faults and shear zones. The foliation-parallel leucosomes are usually 5-20 mm thick. The distribution of most of the leucosomes is controlled by the spatial distribution of pre-existing compositional layer- ...
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... show stromatic fabric with leucosomes commonly concordant to bedding planes, except in high strain zones, such as faults and shear zones. The foliation-parallel leucosomes are usually 5-20 mm thick. The distribution of most of the leucosomes is controlled by the spatial distribution of pre-existing compositional layer- ing and foliation (Fig. 3i). Some boudin-like structures into which leucocratic material has segregated are developed in the inter-boudin partitions (Fig. 3j). Melts have also collected into blasts of sillimanite/andalusite (up to 20 cm), but hornfelses and contact migmatites (injection complex) have a massive structure and granoblastic texture without prismatic ...
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... and shear zones. The foliation-parallel leucosomes are usually 5-20 mm thick. The distribution of most of the leucosomes is controlled by the spatial distribution of pre-existing compositional layer- ing and foliation (Fig. 3i). Some boudin-like structures into which leucocratic material has segregated are developed in the inter-boudin partitions (Fig. 3j). Melts have also collected into blasts of sillimanite/andalusite (up to 20 cm), but hornfelses and contact migmatites (injection complex) have a massive structure and granoblastic texture without prismatic silliman- ite (Fig. 5). In the injection complex, some of the leucocratic veins can be observed adjacent to the plutonic bodies. In ...
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... & Fergusson 2003modified after Moazzen et al. 2004 andSepahi & Athari 2006). SQ - Saqqez, SD - Sanandaj, GH - Ghorveh, AM - Almogholagh, HD - Hamedan (Alvand), AR - Arak, AS - Astaneh, BJ - Boroujerd, AG - Aligudarz, AZ - Azna, MT - Muteh, KG - Kolah-Ghazi, SJ - Sirjan, SK -Siah Kouh. some small shear zones forming the discordant leucosomes (Fig. ...
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... and/or in situ melting in a closed system. Melt trans- fer from grain-scale sites where melting occurred to layer-parallel leucosomes was controlled by the spatial dis- tribution of pre-existing compositional layering and foliation formed by metamorphic segregation, but some times by in situ partial melting (showing pinch and swell structures; Fig. 3i). Some of the leucosomes were generated by meta- morphic differentiation or in situ partial melting showing mafic ...
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... Metamorphic rocks include the widespread Late Triassic to Early Jurassic Hamadan phyllites, interpreted as back-arc deposits and considered a lateral facies variation from the Songor-Kangavar volcanic arc series (Braud and Bellon, 1974). The emplacement of Jurassic calc-alkaline intrusions like Alvand batholith into the Hamadan phyllites resulted in a contact metamorphism event encompassing Hornfels and various spotted foliated rocks, that has been followed by a low-pressure high-temperature regional metamorphism (Abukuma type metamorphism) or low P/T series during Cretaceous Sepahi et al., 2004;Agard et al., 2005;Sepahi et al., 2009;Monfaredi et al., 2020). Shakerardakani et al., (2022) reported a sequential metamorphic evolution in the central SSZ (Dorud-Azna complex) during a Wilson cycle. ...
There are extensive outcrops of regional metamorphic rocks that consist of marble, calcschist, metapelite, and amphibolite in the south Sirjan (southern Sanandaj-Sirjan zone). Garnet, muscovite, biotite, calcite, quartz, and feldspar are the rock-forming minerals of calcschists. Kyanite, garnet, and staurolite constitute the index minerals of the studied metapelites. Amphibole and plagioclase are the main minerals of the massive and foliated amphibolites. The P-T conditions of the regional metamorphic event in the southern SSZ were constrained using conventional (single-reaction) and multi-equilibrium thermobarometry (THERMOCALC software). The average temperature and pressure gained by THERMOCALC software are 8 kb, 643 ˚C, and 9.6 kb, 645 ˚C for Ky-Grt schist and calcschist samples, respectively. Using revised and recalibrated conventional thermobarometry methods result in temperature from 504 to 664 °C and pressure from 6.57 to 7.88 kb for the investigated Ky-Grt schist. Mineralogical paragenesis and thermobarometry results of the investigated metamorphic rocks are in accordance with a medium P/T-type metamorphic gradient. Presumably, Neotethys subduction beneath the Sanandaj-Sirjan zone and resulting crustal thickening event led to such a metamorphic gradient during Eo-cimmerian orogeny. Medium P/T metamorphic rocks of the southern Sanandaj-Sirjan zone and accompanying high P/T metamorphic rocks of the north Hajiabad could be defined as a pair of metamorphic belts that were constructed during Zagros orogeny.
... With respect to the latter lithotype, a metasedimentary origin was firstly highlighted by Miri et al. (2016) who classified them as para-amphibolites. The intrusion of the Middle Jurassic Alvand composite batholith (Figure 1b; Shahbazi et al., 2010;Mahmoudi et al., 2011;Yang et al., 2018;Sepahi et al., 2018Sepahi et al., , 2019Sepahi et al., , 2020Sepahi et al., , 2023Lucci et al., 2023) caused Buchan-type metamorphism and formation of a huge metamorphic aureole and both metapelitic and mafic migmatites (e.g., Sepahi et al., 2009Sepahi et al., , 2023Saki, 2011;Saki et al., 2012Saki et al., , 2020Saki et al., , 2021Baharifar et al., 2018;Monfaredi et al., 2020;Lucci et al., 2021). ...
... Mineral chemistry evolution of metapelitic rocks constituting the Alvand contact aureole were investigated in the last decades (e.g., Baharifar et al., 2004;Agard et al., 2005;Sepahi et al., 2009;Sepahi et al., 2013;Miri et al., 2016;Baharifar et al., 2018;Monfaredi et al., 2020;Saki et al., 2020;Zare Shooli et al., 2020;Sepahi et al., 2023). However, if we exclude the work of Miri et al. (2016) focused on chemical zoning of amphiboles from the studied para-amphibolites, no studies exist at the time of writing related to the chemistry and metamorphic evolution of these peculiar rocks locally found within the metapelites in the Alvand contact aureole. ...
... Whereas in the central SaSZ, it is overlain by a supracrustal arrangement (also reported in literature as "Jurassic metamorphic complex", e.g., Mohajjel et al., 2003;Hassanzadeh and Wernicke, 2016) of Barrovian-type metamorphosed Paleozoic to Early Mesozoic volcanic material interbedded with marbles, meta-psammites, shales and slates (Mohajjel et al., 2003;Baharifar et al., 2004;Hassanzadeh and Wernicke, 2016;Azizi et al., 2018Azizi et al., , 2020. All these crustal materials were then affected by the Jurassic magmatism responsible of the HT/LP Buchan-type metamorphism -mostly in the Hamedan area -and by the subsequent unconformably deposition of the Cretaceous limestones (e.g., Berberian et al., 1982;Hosseiny, 1999;Sepahi et al., 2009Sepahi et al., , 2023Shahbazi et al., 2010Shahbazi et al., , 2014Mahmoudi et al., 2011;Saki et al., 2020Saki et al., , 2021Aliani et al., 2012;Azizi et al., 2018;Yang et al., 2018;Zhang et al., 2018;Baharifar et al., 2018;Baharifar, 2019;Lucci et al., 2021Lucci et al., , 2023. ...
n this work we explore the distribution of rare earth elements (REE) in hornblende-bearing metamorphic rocks from the Jurassic Alvand plutonic complex (Sanandaj-Sirjan Zone, NW Iran) focusing on the understanding the effect of rock-forming silicates in controlling compositional variations during metamorphism. The studied rocks contain two distinct amphibole-dominated paragenesis: a first one including hornblende + epidote + plagioclase (“amphibolite”) and a second on made up of hornblende + garnet + epidote + plagioclase (“garnet amphibolite”). The bulk high Al2O3 (average 17.7 wt%), CaO (average 11.9 wt%) and low Fe2O3* (average 5.9 wt%), MgO (average 2.3 wt%), and TiO2 (average 0.8 wt%) contents together with the Zr/Ti (average 280), Na2O/Al2O3 (average 0.05) and Na2O+K2O (average 1.7 wt%) values indicate these rocks are para-amphibolite formed by metamorphism of a marl (calcareous shale) protolith. With respect to the rock-forming phases, the epidotes have the highest ΣREE contents (ΣREE=86-210 ppm). The garnets (ΣREE=27-87 ppm) and hornblendes (ΣREE=10-22 ppm) have moderate values, whereas the plagioclase shows the lowest REE (2-4.7 ppm) amounts. Inverse and forward modelling thermobarometry was applied to unravel the pressure-temperature history of the studied samples and therefore to reveal the impact of each phase on the REE partitioning during the recorded metamorphic evolution, considering that REE are mostly immobile during crust processes and therefore their bulk budget is that of the protolith.
... These low-to high-grade Buchan and Barrovian-type metamorphic rocks were the host of vigorous magmatic activity during Jurassic to Early Cretaceous time (e.g., Berberian et al., 1982;Sepahi, 1999;Rashidnejad-Omran et al., 2002;Sheikholeslami et al., 2003;Baharifar et al., 2004;Sepahi et al., 2004Sepahi et al., , 2014Sepahi et al., , 2018Sepahi et al., , 2019Sepahi and Athari, 2006;Ahmadi-Khalaji et al., 2007;Shahbazi et al., 2010Shahbazi et al., , 2014Chiu et al., 2013;Azizi et al., 2011Azizi et al., , 2015aAzizi et al., , 2015bAzizi et al., , 2018aAzizi et al., , 2018bYang et al., 2018;Zhang et al., 2018aZhang et al., , 2018bSheikhi-Gheshlaghi et al., 2020). The magmas in the Hamedan area (e.g., Shahbazi et al., 2010;Aliani et al., 2012) produced well-developed contact metamorphic aureoles (e.g., Sepahi et al., 2009;Shahbazi et al., 2010). The magmatism generally interpreted as consequence of the Mesozoic to Cenozoic evolution of the Neotethys geodynamic framework and to the Arabia-Eurasia collisional dynamics (e. g., Sepahi, 1999;Sepahi et al., 2004;Shahbazi et al., 2010;Sepahi et al., 2014Sepahi et al., , 2018Sepahi et al., , 2019, however recently published works (e.g., Azizi et al., 2018aAzizi et al., , 2018Azizi and Stern, 2019) based on chemical signature of mafic magmas in the SaSZ questioned the Jurassic scenario, invoking an extensional event affecting the Cadomian crust of Iran and post-dating the subduction of Neotethys in late Jurassic-early Cretaceous time. ...
... Regional metamorphic zones of chlorite, biotite, garnet, andalusite (chiastolite), staurolite (±andalusite), sillimanite and sillimanite-(±cordierite)-K-feldspar and thermal metamorphic zones of cordieriteandalusite, cordierite-K-feldspar and sillimanite-K-feldspar are widespread in the study area and testify the Si-Al-rich character of the country rocks. A description of metamorphic rocks and zones in the region is provided by Sepahi et al. (2004Sepahi et al. ( , 2009Sepahi et al. ( , 2019. The contact aureole of the APC is also characterized by the presence of both metapelitic and mafic migmatites (Sepahi et al., 2009(Sepahi et al., , 2019Saki et al., 2012Saki et al., , 2021Lucci et al., 2021). ...
... A description of metamorphic rocks and zones in the region is provided by Sepahi et al. (2004Sepahi et al. ( , 2009Sepahi et al. ( , 2019. The contact aureole of the APC is also characterized by the presence of both metapelitic and mafic migmatites (Sepahi et al., 2009(Sepahi et al., , 2019Saki et al., 2012Saki et al., , 2021Lucci et al., 2021). Noteworthy, the metapelitic migmatites are locally characterized by sapphire-bearing granitic leucosomes (e.g., Sheikhi-Gheshlaghi et al., 2020). ...
This work investigates the petrogenesis of the main magmatic rocks of the Jurassic Alvand plutonic complex,
located in the northern sector of the Sanandaj-Sirjan Zone of Iran. The Alvand complex is made up of a wide
range of rocks spanning gabbro to leucogranites, containing a diversified range of enclaves, from mafic-to felsic�and surmicaceous-type. Here we present new textural characterization together with mineral, whole rock and
Sr–Nd isotope chemistry of the main magmatic lithotypes. We integrated this new data with the available ones to
understand the petrogenesis of the Alvand magmas and their interaction with the Ediacaran-Cambrian crystalline
basement. A legacy of the Peri-Gondwanan crust is evident in Alvand felsic rocks. The whole rock chemistry, the
Sr–Nd isotope ratios and assimilation-fractional crystallization numerical models indicate their genesis partly
through differentiation via fractional crystallization from the coeval Alvand gabbros coupled with a concurrent
and significative mass-addition of material from the Cadomian basement. At a wider scale, this work also pro�vides new insights into the understanding the role of the continental crust in the buildup of transcrustal
magmatic systems and therefore to a better comprehension of crust growth process driven by intense magma�crust interaction events.
... Metamorphic rocks in the Hamadan region are mostly metapelites including both regional (i.e., slate, phyllite, schist) and contact metamorphic rocks (i.e., hornfels, hornfels schist, and migmatite) (Fig. 1b). In addition, quartzites, meta-psammites, meta-basites, calc-pelites, and calc-silicates with smaller volumes are present in this region (Sepahi et al. 2009, Sepahi et al. 2018. Slate, phyllite, and schist include garnet, andalusite-garnet, sillimanite-staurolite-andalusite, staurolite, and sillimanite as index minerals, and spotted schist and hornfels contain cordierite, andalusite-cordierite, garnet-andalusite-sillimanite, sillimanite, and sillimanite-alkali feldspar (Baharifar et al. 2019). ...
... Slate, phyllite, and schist include garnet, andalusite-garnet, sillimanite-staurolite-andalusite, staurolite, and sillimanite as index minerals, and spotted schist and hornfels contain cordierite, andalusite-cordierite, garnet-andalusite-sillimanite, sillimanite, and sillimanite-alkali feldspar (Baharifar et al. 2019). The migmatites occur in the southeast of the Alvand intrusive complex (Sepahi et al. 2009, Saki et al. 2012 , Fig 1b). Melanosome in these rocks is composed of biotite þ sillimanite þ garnet þ cordierite þ spinel 6 orthopyroxene, and leucosomes contain garnet þ plagioclase þ alkali feldspar þ quartz. ...
Pegmatite bodies with a simple mineral composition are widespread within the Sanandaj-Sirjan Zone (SaSiZ), Zagros Orogen, Iran; however, gem-bearing pegmatite bodies are rare. There is a pegmatitic vein within the Hamadan garnet (± andalusite ± staurolite) schist adjacent to the Alvand Plutonic Complex (APC), south of Hamedan city (western Iran), in which large crystals of gem spodumene occur together with quartz, amazonite, beryl, tourmaline, and apatite. This spodumene-bearing pegmatite consists of four major zones with slightly different mineral compositions from the border to the core. The wall zone of quartz-rich granitoid and the intermediate zone of alkali granite have trondhjemitic compositions near the quartzolitic gem-bearing core zone. All parts of the vein are peraluminous in composition and exhibit S-type affinity. Two types of spodumene which have been distinguished in the core zone are colorless to very pale yellow and pink, transparent with vitreous luster and inclusion-free (eye clean) under 10× magnification. The different color in these minerals can be attributed to the slightly different chemical compositions, particularly lower Fe/Mn ratios in the pink material. The δ7Li values of the spodumene (+5.58 to +6.57‰) are indicative of the incorporation of middle continental crustal components in their genesis. Change in the mineral assemblage from tourmaline-bearing in the intermediate zone to spodumene + tourmaline in the core zone of the spodumene-bearing pegmatite is consistent with increasing lithium content from the wall zone to the core. Petrographic, geochemical, and isotopic data indicate that partial melting of middle-crustal Al-rich metapelitic source was followed by fractional crystallization to generate these rocks. In this concern, the required Li for the crystallization of spodumene was probably supplied by the breakdown of staurolite of the Hamadan schist and/or subsequent fractional crystallization of the parent magma. The results also demonstrate that the regional tectonic regime exerts a primary control on the occurrence and emplacement of the miarolitic pegmatite in the upper crust and the formation of gem spodumene during late-stage magmatic activities.
... The C-SaSZ, where the Alvand plutonic complex and the study area are located, is characterized by (i) Cadomian basement dominated by metagranites and amphibolites (Badr et al. 2018;Azizi and Stern 2019); (ii) the Jurassic metamorphic complex (Mohajjel and Fergusson 2000;Mohajjel et al. 2003;Agard et al. 2005;Hassanzadeh and Wernicke 2016;Azizi and Stern 2019) with protoliths interpreted as mafic to felsic volcanic rocks interbedded with carbonates and siliciclastic materials deposited over a thin Cadomian crust in a marine basin setting (e.g., Mohajjel et al. 2003;Baharifar et al. 2004;Hassanzadeh and Wernicke 2016;Azizi et al. 2018a, b); and (iii) the Jurassic to Early Cretaceous gabbro to granite intrusive complexes (Saki et al. 2021 and references therein). The latter magmatic activity heated the pre-existing rocks and generated Buchan-type thermo-metamorphic contact aureoles characterized by Al 2 SiO 5bearing hornfels up to migmatization (e.g., Baharifar et al. 2004;Agard et al. 2005;Sepahi et al. 2009Sepahi et al. , 2018Sepahi et al. , 2019Sepahi et al. , 2020Shahbazi et al. 2010Shahbazi et al. , 2014Mahmoudi et al. 2011;Hassanzadeh and Wernicke 2016;Saki et al. 2020). ...
... Minor occurrences of these mafic rocks are also observed in the eastern sector of the Alvand complex, in the Simin-Khaku locality (Eghlimi 1998;A.A. Sepahi, personal communication). Existing literature on the CG gabbros (Eshraghi and Mahmoudi Gharai 2003;Sepahi et al. 2009;Shahbazi et al. 2010;Yang et al. 2018;Saki et al. 2020) permits their discrimination between (i) hornblende-free olivinegabbros (hereafter Ol-gabbro) with pyroxenite lenses and (ii) hornblende-bearing gabbros (hereafter Hbl-gabbro) and diorites. A primary contact between these two gabbroic lithotypes is locally observed (e.g., Saki et al. 2021); however, a detailed field study is still missing. ...
... The intrusive Alvand plutonic complex generated a welldeveloped thermo-metamorphic aureole made up of cordierite-andalusite-sillimanite-bearing hornfels and cordierite-bearing migmatites (e.g., Sepahi et al. 2019;Saki et al. 2020) in the local low-grade regional metamorphic basement (known in literature as "Hamedan Phyllite," e.g., Mohajjel et al. 2003). Peak conditions for the thermal aureole were estimated at~750°C and 4 kbar (Sepahi 2008, Sepahi et al. 2013Sepahi et al. 2009Sepahi et al. , 2013Sepahi et al. , 2020Saki et al. 2012Saki et al. , 2020Baharifar et al. 2004;Shahbazi et al. 2014;Sheikhi Gheshlaghi et al. 2020). The metapelitic migmatites show a U-Pb zircon age of~170 Ma (Sepahi et al. 2019), and are mostly found in the eastern (Simin-Khaku locality) and southern (Tuyserkan locality) sectors of the inner aureole (e.g., Saki et al. 2021). ...
Amphibole-dominated dehydration melting of gabbro is the primary process responsible for the genesis of adakites, low-K tonalites, modern trondhjemites, and plagiogranites as well as Archean tonalite-trondhjemite-granodiorite suites that represent the earliest examples of continental crust. Previous literature has mostly focused on the role of Al-rich amphibole during anatexis of a mafic source and many of these studies have investigated this process through experimental melting runs. However, due to experimental boundary conditions, little is known about partial melting of amphibole-bearing mafic rock at temperatures < 800°C for upper crustal conditions (pressure < 500 MPa). Classic and forward thermobarometric modelling suggests that in situ trondhjemite leucosomes, hosted by Cheshmeh-Ghasaban mafic metatexites (Alvand Plutonic Complex, Hamedan, NW Iran), represent a rare natural case study of a low-temperature incipient amphibole-dominated anatectic event of a mafic source with a primary assemblage (Pl+Hbl+Cpx+Bt+Opx) typical of a hornblende-bearing gabbroic rock.
... The geology of the SaSZ (e.g., Berberian and King 1981;Besse et al. 1998;Mohajjel and Fergusson 2000;Mohajjel et al. 2003;Ghasemi and Talbot 2006;Jahangiri 2008, 2009;Hassanzadeh and Wernicke 2016), petrology of igneous rocks (e.g., Ahmadi-Khalaji et al. 2007;Mazhari et al. 2011;Azizi and Asahara 2013) and metamorphic rocks (e.g., Berberian 1977;Rachidnejad-Omran et al. 2002;Baharifar et al. 2004;Sepahi et al. 2004Sepahi et al. , 2009Moritz et al. 2006;Davoudian et al. 2008;Sheikholeslami et al. 2008;Azizi et al. 2011a;Monfaredi et al. 2020) were well documented, but its evolution was refined recently by dating of intrusions (e.g., Masoudi et al. 2002;Shahbazi et al. 2010;Ahadnejad et al. 2011;Azizi et al. 2011bAzizi et al. , 2015aMahmoudi et al. 2011;Alirezaei and Hassanzadeh 2012;Esna-Ashari et al. 2012;Chiu et al. 2013;Fazlnia et al. 2013;Sepahi et al. 2014Sepahi et al. , 2018 In the Malayer-Boroujerd-Shazand district, several pegmatite dike swarms are hosted by both metamorphic rocks and granitoid intrusions. Although intrusions in the Malayer-Boroujerd-Shazand districts were studied in detail by Masoudi et al. (2002), Ahmadi-Khalaji et al. (2007), Ahadnejad et al. (2008Ahadnejad et al. ( , 2011 and Deevsalar et al. (2018); however, a few literatures on the pegmatite fields focused only on the tourmaline chemistry in the SE Boroujerd (Tabbakh Shabani et al. 2013) and on the role of magmatic and metamorphic fluids in the pegmatite development (Masoudi and Yardley 2005). ...
Pegmatite dikes in the Malayer–Boroujerd–Shazand magmatic complex, located in the Sanandaj-Sirjan zone of the Zagros orogen, are hosted in both granitoid rocks and their contact and regional metamorphic aureoles. In this study, we report the geochronology, geochemistry and mineral chemistry of these pegmatite dikes. The granitoid rocks in the Malayer–Boroujerd–Shazand magmatic suites are mainly monzogranite, quartz diorite, granodiorite and quartz monzonite characterized by metaluminous to peraluminous I-type compositions of the calc-alkaline series and display the geochemical characteristics of volcanic arc granites related to an active continental margin. The pegmatite dikes mainly consist of quartz, feldspar (albite and orthoclase), tourmaline, muscovite and less common biotite and garnet. The tourmaline content in the igneous-hosted pegmatite dikes is higher than those of metamorphic rocks, whereas the muscovite content is lower in the igneous-hosted pegmatite dikes. The K/Rb ratio and the Rb content of pegmatite dikes and their minerals (K-feldspar and muscovite) indicate that they are less evolved. Pegmatite dikes display a typical calc-alkaline affinity of I-type granites and are classified as peraluminous Lithium-Caesium-Tantalum (LCT) family (barren sub-type) to muscovite class. The tourmaline is a schorl-foitite type, which is common in the early crystallization stage of less evolved pegmatites. U–Pb zircon dating of the Boroujerd and Shazand pegmatite dikes yield weighted mean 206Pb/238U ages of 160.2 ± 1.8 and 121.8 ± 1.5 Ma, respectively. In contrast, U–Pb zircon dating of the Malayer pegmatite dike gives a mean 206Pb/238U age of 43.2 ± 1.5 Ma. Our new geochronological data indicate that the first group of pegmatite dikes (older pegmatite dikes) in the Boroujerd district (160.2 ± 1.8 Ma) shows an overlap with the main and first magmatic episode in the Sanandaj–Sirjan zone during Jurassic times, simultaneous with the Middle Cimmerian Orogenic phase, and formed during the subduction initiation. The second group of pegmatite dikes in the Shazand district (121.8 ± 1.5 Ma) formed in the Early Cretaceous and shows a temporal overlap with previously reported ages (ca. 130–114 Ma) during the early Alpine tectonic movements (Late Cimmerian Orogenic phase). Finally, the younger group of pegmatite dikes in the Malayer district (43.2 ± 1.5 Ma) formed in the Eocene overlapping with previously reported ages (ca. 34–52 Ma) which is equivalent to the Laramian phase. These data reveal that the magmatism in the Malayer–Boroujerd–Shazand magmatic complex started in the Early-Middle Jurassic resembling adjacent areas in the Sanandaj–Sirjan zone (e.g., Hamedan region) by melting of crustal protoliths in a subduction tectonic setting. The second and third groups of pegmatite dikes formed during the late subduction to syn-collisional process, respectively. These pegmatite generation marked the subduction initiation to syn-collisional span in the region. The zircon geochemistry (negative Ce anomalies and positive Eu anomalies) is indicative of the relatively oxidized conditions of the parent magma and shows characteristics of continental crust zircon.
... (APC) in the Hamedan area (e.g., Shahbazi et al. 2010;Aliani et al. 2012), produced thermo-metamorphic contact aureoles characterized by Buchan-type facies series (e.g., Baharifar et al. 2004;Agard et al. 2005;Sepahi et al. 2009;Shahbazi et al. 2010;Hassanzadeh and Wernicke 2016;Saki et al. 2020). The high-temperature and lowpressure (HT/LP) thermo-metamorphism was also responsible for local migmatization processes (e.g., Sepahi et al. 2009;Saki et al. 2020;Sheikhi Gheshlaghi et al. 2020). ...
... (APC) in the Hamedan area (e.g., Shahbazi et al. 2010;Aliani et al. 2012), produced thermo-metamorphic contact aureoles characterized by Buchan-type facies series (e.g., Baharifar et al. 2004;Agard et al. 2005;Sepahi et al. 2009;Shahbazi et al. 2010;Hassanzadeh and Wernicke 2016;Saki et al. 2020). The high-temperature and lowpressure (HT/LP) thermo-metamorphism was also responsible for local migmatization processes (e.g., Sepahi et al. 2009;Saki et al. 2020;Sheikhi Gheshlaghi et al. 2020). Both metamorphic and magmatic rocks were then unconformably covered by unmetamorphosed Cretaceous limestones (e.g., Hosseiny 1999;Azizi et al. 2018a and references therein;Yang et al. 2018). ...
... Hassanzadeh et al. 2008;Mahmoudi et al. 2011;Hassanzadeh and Wernicke 2016;Sepahi et al. 2018Sepahi et al. , 2020. Here we present an abbreviated geological summary of the Hamedan area and the APC (Figure 1b-c), based on the existing recent detailed literature (Yang et al. 2018;Azizi et al. 2018aAzizi et al. , 2018bShahbazi et al. 2010Shahbazi et al. , 2014Aliani et al. 2012;Sepahi 2008Sepahi , 2013Sepahi et al. 2009Sepahi et al. , 2014Sepahi et al. , 2018Sepahi et al. , 2019Sepahi et al. , 2020Saki 2011;Saki et al. 2012Saki et al. , 2020Hassanzadeh and Wernicke 2016;Baharifar et al. 2004;Mohajjel et al. 2003;Chiu et al. 2013;Mahmoudi et al. 2011;Sheikhi Gheshlaghi et al. 2020). ...
This work describes the petrogenesis of in situ and in-source trondhjemite leucosomes generated by low-degree partial melting of the Jurassic Cheshmeh-Ghasaban hornblende-gabbros in the northern Alvand batholith (Hamedan, NW Iran). These leucosomes occur in a metatexite migmatite as patches, net-structures, veinlets, and dikes at scales ranging from a few millimetres to a few metres. They have high SiO2 (mean ≈ 78 wt%) and Na2O (4–5 wt%) with low Al2O3 (<15 wt%), K2O (<1.5 wt%), Sr (33–267 ppm), Eu (0.31–0.62 ppm) and heavy REE (<4 ppm) contents similar to typical low-Al2O3 trondhjemites. Batch-melting models indicate these leucosomes are the result of ≈1-2% partial melting of the hornblende-gabbro, whereas thermobarometric modelling constrains their petrogenesis in the field of hornblende hornfels-facies metamorphism (pressure ≈3.0–4.5 kbar and temperature ≈700-750°C). On a wider scale, our results document natural trondhjemites generated in the upper crust by amphibole-dehydration melting of a mafic source at temperature conditions close to the solidus, filling the existing gap of data in low-pressure (P < 5kbar) and low-temperature (T < 800°C) amphibole-dominated partial melting experiments. The genesis of these trondhjemites is then discussed with respect to the Mesozoic evolution of the Alvand plutonic complex.
... Many Ghasemi and Talbot 2006) showing the location of the study area; b geologic map of the Alvand complex (after Amidi and Majidi 1977) and locations of the studied migmatites; c authors (e.g. Baharifar et al. 2004;Sepahi et al. 2004;Sepahi et al. 2009;Saki 2011;Saki et al. 2012;Baharifar et al. 2019) have studied the geological setting, mineral chemistry and formation of the pelitic migmatites. It has been concluded that formation of these migmatites was associated with intrusion of mafic magmas into the meta-pelites during the Middle Jurassic (e.g. ...
... Metamorphism is dominantly Buchantype facies series (e.g. Baharifar et al. 2004;Sepahi et al. 2009), however, Barrovian-type metamorphism has been reported in some places (e.g. Hassanzadeh et al. 2008). ...
... The high T/low P (HT/LP) metamorphism in the area is characterized by chlorite, biotite, garnet, andalusite, staurolite, sillimanite, and sillimanite-K-feldspar zones. These zones crop out irregularly due to intense deformation related to thrusting after regional metamorphism (Sepahi et al. 2009). Contact metamorphic rocks including cordierite-, andalusiteand garnet-bearing hornfelses formed next to the Alvand pluton. ...
Subduction of Neo-Tethys oceanic lithosphere beneath the Iranian plate during the Mesozoic formed several igneous bodies of ultramafic to intermediate and felsic composition. Intrusion of these magmas into a regional metamorphic sequence (the Sanandaj-Sirjan Zone) caused partial melting and formation of migmatites with meta-pelitic protoliths. The Alvand complex (west Iran) is a unique area comprising migmatites of both mafic and pelitic protoliths. In this area, the gabbroic rocks contain veins of leucosome at their contact with pyroxenite and olivine gabbro. These leucosomes are geochemically and mineralogically different from leucosomes of the meta-pelitic migmatites and clearly show properties of I-type granites. Microscopic observations and whole rock compositions of the mafic migmatite leucosomes show that migmatization occurred through partial melting of biotite, hornblende and plagioclase. Thermobarometric calculations indicate 800 °C and 3.7 kbar for partial melting, although phase diagram modeling demonstrates that the presence of water could decrease the solidus temperature by about 40 °C. Our results suggest an asthenospheric magma upwelling as the source of heat for partial melting of the gabbroic rock during subduction of Neo-Tethys oceanic crust under the western edge of the Iranian plate. The present study also reveals relationships between migmatization and formation of S- and I -type granites in the area.
... The study area is located in the Sanandaj-Sirjan zone (Fig. 1); the metamorphic rocks of two ages mainly consist of Paleozoic to early Mesozoic and Mesozoic to early Cenozoic (Aliani et al. 2012). The Metapelitic rocks are abundant in this area and comprise phyllites, mica-schists, garnet-schists, garnet-andalusite-(± sillimanite/± kyanite)schists, garnet-stauroliteschists and garnet-sillimanite-(± kyanite)-schists (Sepahi et al. 2009). Soils in Bahar county are mainly calcareous and clays in the soils consist of illite, smectite, chlorite, and vermiculite, and small amounts of kaolinite and quartz (Jalali 2007a). ...
The application of chemical and organic fertilizers to agricultural lands increases nutrient pools and affects soil and water quality. Understanding changes in groundwater quality due to the anthropogenic activities over time is important to human and ecosystem health. In 2017, we resampled 58 wells monitored in the year 2000 to evaluate the rate of changes in groundwater quality and water quality indices over time in response to agricultural and industrial activities and climate changes. The groundwater in two sampling years was dominated by Ca–HCO3 water type. The mean groundwater pH, electrical conductivity (EC), calcium (\({\text{Ca}}^{2 + }\)), magnesium (\({\text{Mg}}^{2 + }\)), and sodium (\({\text{Na}}^{ + }\)) concentrations did not significantly change over time, while a significant buildup in bicarbonate \(({\text{HCO}}_{3}^{ - } )\) (189–305 mg l−1), nitrate (\({\text{NO}}_{3}^{ - }\)) (41–56 mg l−1), chloride (\({\text{Cl}}^{ - }\)) (57–77 mg l−1) and a significant decrease in sulfate (\({\text{SO}}_{4}^{2 - }\)) (159–91 mg l−1) and potassium (\({\text{K}}^{ + }\)) (3–2 mg l−1) was observed. In 2000, 45% of the water samples were classified as high salinity hazard, and this value increased to 52% by 2017, indicating that salinity of the water samples increased over 17 years. In 2000, only 25% of the total area had a \({\text{NO}}_{3}^{ - }\) value greater than 50 mg l−1; and this value increased sharply to 62% by 2017, indicating that \({\text{NO}}_{3}^{ - }\) concentrations significantly increased with approximately 2.2% annually in groundwater, over 17 years. Approximately, 55% of the groundwaters with \({\text{NO}}_{3}^{ - }\) concentration values of less than 40 mg l−1 in 2000 shifts one to four categories upward in 2017. The percentage of water samples which was shifted to the next category with \({\text{NO}}_{3}^{ - }\) concentration higher than 50 mg l−1 and approaching the limit of the World Health Organization was doubled in 2017 compared with 2000. High application of chemical and manure fertilizers in excess of crop needs should be avoided in the studied area to prevent continued increases in groundwater \({\text{NO}}_{3}^{ - }\) concentrations.
... However, no supporting age data for the proposed Late Cretaceous metamorphic event are available. Sepahi et al. (2009) andSaki et al. (2012) calculated peak metamorphic conditions of ~ 650-750 °C and ~ 2-4 kbar by means of conventional thermobarometry methods in migmatites occurring adjacent to the Alvand composite pluton. Maximum P-T conditions of 700-750 °C at 5-6 kbars were recently presented for the high-grade metamorphic mafic rocks from the metamorphic aureole around the pluton (Sepahi et al. 2013). ...
