Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Solid Earth Discuss., 6, 2321–2370, 2014 www.solid-earth-discuss.net/6/2321/2014/ doi:10.5194/sed-6-2321-2014 SED © Author(s) 2014. CC Attribution 3.0 License. 6, 2321–2370, 2014 This discussion paper is/has been under review for the journal Solid Earth (SE). Magma storage and Please refer to the corresponding final paper in SE if available. plumbing of adakite-type Magma storage and plumbing of post-ophiolite intrusions adakite-type post-ophiolite intrusions in K. Jamshidi et al. the Sabzevar ophiolitic zone, NE Iran Title Page K. Jamshidi1,2, H. Ghasemi1, V. R. Troll2, M. Sadeghian1, and B. Dahren2 Abstract Introduction 1Faculty of Earth Sciences, Shahrood University, Shahrood, Iran 2Department of Earth Sciences, CEMPEG, Uppsala University, Uppsala, Sweden Conclusions References Received: 24 July 2014 – Accepted: 24 July 2014 – Published: 8 August 2014 Tables Figures Correspondence to: K. Jamshidi ([email protected]) J I Published by Copernicus Publications on behalf of the European Geosciences Union. J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 2321 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract SED Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous- Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite 6, 2321–2370, 2014 in composition. Here we investigate the magma supply system to these subvolcanic 5 intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium Magma storage and models, including amphibole thermobarometry, plagioclase-melt thermobarometry and plumbing of clinopyroxene-melt barometry. Based on the results of these thermobarometric models, adakite-type plagioclase crystallized dominantly at pressures of ∼ 350 (468–130) MPa, while amphi- post-ophiolite boles record both low pressures (∼ 300 MPa) and very high pressures (> 700 MPa) of intrusions 10 crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and K. Jamshidi et al. no plagioclase in the most primitive samples (Mg-andesites) is consistent with am- phibole fractionation from very hydrous magmas at deep crustal levels of the plumb- ing system, which may have been a key process to intensify adakite-type affinities Title Page 15 in this rock suite. Barometry, combined with frequent disequilibrium features, such as Abstract Introduction oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper Conclusions References crustal magma system that developed progressively stronger compositional modifica- Tables Figures tions during high-level magma storage. J I 20 1 Introduction J I The Sabzevar ophiolitic zone (SOZ) in northeast Iran is part of the eastern Tethyan Back Close ophiolite belt and represents a remnant of the Cretaceous Tethyan ocean lithosphere Full Screen / Esc which was obducted in late Cretaceous to early Paleocene time (Shojaat et al., 2003). The ophiolite belt contains ultramafic rocks (harzburgite, dunite and lherzolite), small Printer-friendly Version 25 masses of gabbro, and a thick sequence of submarine basaltic lavas (Shojaat et al., 2003; Khalatbari Jafari et al., 2013). The ophiolite is intruded by widespread subvol- Interactive Discussion 2322 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | canic stocks and dykes of intermediate to felsic compositions and the main purpose of this study is to investigate the compositional spectrum and ascent history of these SED post-ophiolite subvolcanic rocks. 6, 2321–2370, 2014 The detailed evolution and ascent history of the Sabzevar post-ophiolite rocks has 5 not been investigated previously and we present new major and trace element data on whole rocks plus major element data from the main minerals to improve our knowledge Magma storage and on the history of the post-ophiolite intrusive suite. We attempt to compare post-ophiolite plumbing of felsic rocks in the southern Sabzevar belt with dominantly intermediate ones in the adakite-type North and aim to test if differences between the post-ophiolite subvolcanic rocks of the post-ophiolite 10 two sectors exist. Finally, we hope to establish the P -T conditions of amphibole and intrusions plagioclase crystallization through mineral-melt equilibrium thermobarometry to help reconstruct the former plumbing system to these rocks. K. Jamshidi et al. Amphibole occurs as essential rock forming mineral in a wide variety of igneous and metamorphic rocks and is especially abundant in calc-alkaline igneous rocks. Experi- Title Page 15 mental studies have synthesized amphibole over a pressure range of up to 2300 MPa ◦ ◦ and 400 C to 1150 C in calc-alkaline compositions (Blundy and Holland, 1990) and Abstract Introduction amphibole has therefore considerable potential as an indicator of crystallization condi- Conclusions References tions, both as geothermometer and geobarometer (Blundy and Holland, 1990; Ridolfi, 2010). Tables Figures 20 The composition and growth morphology of igneous feldspar usually reflects pro- gressive changes in crystallization conditions that give a reliable record of crystalliza- J I tion dynamics of an associated melt and its thermal and compositional history (e.g. Troll and Schmincke, 2002; Slaby and Götze, 2004). In the studied rocks, amphibole and J I plagioclase are found most widely in the northern suite of intermediate rocks and we Back Close 25 employed the thermobarometers of Ridolfi and Renzulli (2012) for selected amphiboles Full Screen / Esc to determine crystallization and storage conditions for these rocks. Plagioclase-liquid thermobarometry (Putirka, 2008) and clinopyroxene-melt barometry (Putirka, 2008) Printer-friendly Version were employed in order to complement and test the results from amphibole thermo- barometry. Interactive Discussion 2323 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 Geological setting SED The Sabzevar ophiolite zone is ∼ 200 km long and ∼ 10 km wide and represents a tec- tonically dismembered ophiolite complex, located along the northern boundary of the 6, 2321–2370, 2014 Central Iranian microcontinent (Shojaat et al., 2003). Plate tectonic reconstructions 5 suggest that the Sabzevar ophiolite was part of the Tethyan Ocean that formed during Magma storage and Cretaceous rifting from a narrow but deep seaway, separating the Central Iranian mi- plumbing of crocontinent from the Eurasian plate. The ophiolite was emplaced during an episode adakite-type of northeast dipping subduction (i.e. closure) of the Tethyan seaway (the Sabzevar post-ophiolite Ocean) in Upper Cretaceous–early Paleocene time (Shojaat et al., 2003). The em- intrusions 10 placement of the Sabzevar ophiolitic belt was followed by lasting post-ophiolite volcan- ism from at least the Eocene (∼ 40 Ma) to the end of the Pliocene (∼ 2.3 Ma) (Lensch K. Jamshidi et al. et al., 1977; Spies et al., 1983; Shojaat et al., 2003). This Eocene volcanism is ex- pressed in central and in northern Iran (Berberian and King, 1981; Berberian et al., 1982; Bina et al., 1986; Stampfli and Borel, 2002; Agard et al., 2005; Shabanian et al., Title Page 15 2012) and Eocene volcano-sedimentary rocks cover extensive areas in the Sabzevar Abstract Introduction region. Since the Oligocene, volcanism has been intermittent (Jahangiri, 2007) and, for ∼ 10 Ma focussed predominantly on the Turkish-Iranian plateau (e.g., Berberian and Conclusions References Berberian, 1981; Keskin et al., 1998; Azizi and Moinevaziri, 2009). The Oligo-Miocene Tables Figures sedimentary rocks are composed of marine flysch-type facies in their lower parts, while 20 younger facies are of continental origin and contain, in some parts, extremely high per- J I centages of volcanic detritus. These sedimentary rocks are tectonically imbricated, often steeply dipping and penetrated by Oligocene alkali-olivine-basalt magmatism J I (Ghasemi et al., 2011). Following the Eocene volcanic and volcano-sedimentary and Back Close the Oligocene volcanic activity, magmatism recommenced in the region and continued Full Screen / Esc 25 to the end of the Pliocene. In the Sabzevar belt, characteristically, post-ophiolite subvol- canic rocks occur in the north and in the south of the ophiolite zone (Fig. 1) and mag- matism comprised intermediate rocks in the northern part, while felsic rocks dominate Printer-friendly Version the southern part (Fig. 2). Fragments of host rocks, including serpentinized harzbur- Interactive Discussion 2324 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | gites, tuffaceous siltstone and marl are found in some intrusions as xenoliths (Fig. 3). Large volumes of detritus originated from these intrusive domes, forming Pliocene- SED Pleistocene conglomerates (Fig. 3d), which indicate that the studied domes eventually 6, 2321–2370, 2014 outcropped at the Earth’s surface around the Miocene-Pliocene boundary (Salehine- 5 jad, 2008). Magma storage and plumbing of 3 Method adakite-type post-ophiolite 3.1 Analytical techniques intrusions Twenty-three fresh whole rock samples from the northern sector and 24 samples from K. Jamshidi et al. the southern sector were selected for major and trace element analysis at AMCE an- 10 alytical laboratory, Vancouver, Canada.