Mineral chemistry and thermobarometry of plutonic, metamorphic and anatectic rocks from the Tueyserkan area (Hamedan, Iran)

Abstract

1 De part ment of Ge ol ogy, Bu-Ali Sina Uni ver sity, Hamedan, Iran Sepahi A. A., Borzoei K., Sa lami S. (2013) Min eral chem is try and thermobarometry of plutonic, meta mor phic and anatectic rocks from the Tueyserkan area (Hamedan, Iran). Geo log i cal Quar terly, 57 (3): 515-526, doi: 10.7306/gq.1108The study area is a part of the NW to SE strik ing Sanandaj-Sirjan meta mor phic belt in west ern Iran. The Alvand Pluton, consist ing of rocks that range in com po si tion from gab bro to gran ite, is the ma jor mag matic rock com plex of this area. Gabbroic rocks in clude ol iv ine gab bro, gab bro norite, norite and gab bro. Rocks around the Alvand Pluton were sub jected to dif fer ent P-T con di tions due to polymetamorphism. Com mon meta mor phic rocks are meta-pelites, but some meta-psammites, meta-basites and meta-car bon ates also oc cur. Slates, phyllites, schists, migmatites and hornfelses are ma jor rock units of meta-pelites in the meta mor phic se quence. Based on min eral chem is try, the high est tem per a ture of crystallisation (1300°C) was de ter mined for the ol iv ine gab bros, and the low est tem per a ture (950°C) was cal cu lated for the hornblende-bear ing gabbros. Clinopyroxene-plagioclase ba rom e try sug gests that pres sures near 5 to 6 kbars pre vailed dur ing the crystallisation of the var i ous mafic rocks. P-T es ti mates yield max i mum tem per a tures of 700-750°C at 5-6 kbars for the high-grade meta morphic rocks from the meta mor phic au re ole around the pluton. These re sults in di cate that the heat re leased from the Alvand Pluton (T = 950-1300°C), which in truded the meta mor phic rocks at mid dle and up per crustal lev els, was suf fi cient to cause par tial melt ing lead ing to for ma tion of the metatexites, diatexites and restite-rich S-type gran ites. Dur ing this pro cess, part of the deep-seated gab bro-dioritic rocks were trans ported to higher crustal lev els by vis cous, en clave-and crys tal-rich gra nitic mag mas of the par tial melt ing zone.

Geochemistry and Sr–Nd isotopic characteristics of ferroan-magnesian metaluminous granites of the NW Sanandaj–Sirjan zone, Iran: granite formation in a compressional–extensional setting during Late Jurassic time

“…For example, recently Azizi & Stern (2019) presented a propagating rift model to interpret Jurassic magmatism in the region, but on the basis of huge volumes of calc-alkaline plutonic rocks, this model may not be a model that correlates with geological observations. We agree with most other authors such as Torkian et al (2008), Shahbazi et al (2010), Agard et al (2011), Sepahi et al (2013, 2018) and Hassanzadeh & Wernicke (2016), who have argued for a subduction-related environment (continental arc or active continental margin) for a petrogenetic interpretation of the region in Jurassic time.…”

Deciphering the Jurassic–Cretaceous evolution of the Hamadan metamorphic complex during Neotethys subduction, western Iran

“…Sepahi et al (2009) and Saki 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). Based on amphibole composition and hornblende-plagioclase thermometry, thermobarometric calculations of Miri et al (2016) provided P-T conditions of 492-508 °C and 4.3-4.9 kbar for the cores of these minerals and 552-573 °C and 5.5-5.9 kbar for the outer rims, respectively.…”

Genesis of trondhjemite by low-pressure low-melt fraction anatexis of hornblende-gabbro at Alvand Plutonic Complex (Hamedan, NW Iran): insights from geochemical modelling

“…These geochronology studies suggest that CG gabbros emplaced at ≈161-167 Ma (Shahbazi et al 2010;Yang et al 2018). Furthermore, Sepahi et al (2013) used classic thermobarometry modelling to estimate emplacement temperatures of 1200-1300°C and 900-1100°C for Ol-gabbros and Hbl-gabbros, respectively, at crustal conditions of ≈ 5-6 ± 2.5 kbar for both.…”

“…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).…”