Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, northeast Iran

Abstract

Abstract. Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, northeast Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclasemelt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ∼ 350 (130 to 468) MPa, while amphiboles record both low pressures (∼ 300 MPa) and very high pressures (> 700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process in intensifying adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, implies that final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

Petrology, petrogenesis, and geochronology review of the Cenozoic adakitic rocks of northeast Iran: Implications for evolution of the northern branch of Neo‐Tethys

“…The specific focus of this analysis is magmatism in the northern part of the CISZ, which includes smaller magmatic belts, such as Torud–Ahmad Abad, Abbas Abad–Davarzan‐Sabzevar, and Qouchan–Esfarayen (Yousefi, 2017; Yousefi, Sadeghian, Samyari, & Ghasemi, 2017). These areas have also been mentioned by Jamshidi et al (2015) and Gardideh et al (2018), where recent research has been carried out in these regions as well.…”

“…The association of these hypabyssal magmatic rocks and melting Neo‐Tethys oceanic plate has been widely accepted by researchers (Ghasemi & Rezaei Kahkhaei, 2015; Jamshidi et al, 2015; Yousefi, Sadeghian, Samyari, & Ghasemi, 2017; Yousefi, Sadeghian, Wanhainen, et al, 2017). According to geothermobarometry of some phenocrysts, such as amphibole, plagioclase, and pyroxene, in these adakites in some of these regions, the depth of the beginning of magma crystallization (before shallow emplacement) is estimated to be <30 km (Jamshidi et al, 2015; Yousefi, Sadeghian, Wanhainen, et al, 2017). Our focus is on the three neighbouring areas, where magmatism occurred, that is, Sabzevar, Qouchan‐Esfarayen, and south to southeast Shahrood.…”

“…Also Maghdour‐Mashhour, Esmaeily, Shabani, Chiaradia, and Latypov (2015) have pointed to volcanic and plutonic rocks that outcrop in central (Urumieh–Dokhtar Magmatic Assemblage, UDMA) and north–northeastern Iran (Alborz Magmatic Belt, AMB); they proposed that this magmatism marked the beginning of subduction of the Neo‐Tethyan oceanic lithosphere beneath the south–southwestern border of the Turkish–Iranian high plateau and was approximately simultaneous with the closure of Palaeotethys in southern Eurasia during the Late Permian–Early Triassic. In several parts of the Central Iran Structural Zone (CISZ), there are numerous intrusions with intermediate to felsic compositions with adakitic geochemical signatures (Gardideh, Ghasemi, & Sadeghian, 2018; Jamshidi, Ghasemi, Miao, & Sadeghian, 2018; Jamshidi, Ghasemi, Troll, Sadeghian, & Dahren, 2015; Yousefi et al, 2017).…”

Oxygen isotope heterogeneity of arc magma recorded in plagioclase from the 2010 Merapi eruption (Central Java, Indonesia)

“…However, several lines of evidence allow us to rule out this possibility. First, plagioclase crystallizing from adakite-type magmas usually has lower anorthite contents (An 27-80 ) (e.g., Prouteau and Scaillet, 2003;Jamshidi et al, 2015) than the 2010 Merapi plagioclase cores. Second, it seems to be problematic to produce the anorthite-rich plagioclases (An ≥90 ) by closed-system crystallization of the bulk-rock 2010 Merapi basaltic andesite at any crustal depths, as shown by Costa et al (2013).…”

Plagioclase Hosted Melt Inclusion in Hypabyssal Rocks in Torud-Ahmad Abad Magmatic Belt

“…1). different parts of the collision zone (Jamshidi et al, 2015;Motaghi et al, 2012;Shabanian et al, 2012). During the Mesozoic and Cenozoic, central Iran was a tectonically dynamic region.…”