Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: a case study from Ciomadul volcano (SE Carpathians)

Abstract

10 Abstract Ciomadul is the youngest volcano in the Car-11 pathian-Pannonian region produced crystal-rich high-K 12 dacites that contain abundant amphibole phenocrysts. The 13 amphiboles in the studied dacites are characterized by large 14 variety of zoning patterns, textures, and a wide range of 15 compositions (e.g., 6.4-15 wt% Al 2 O 3 , 79-821 ppm Sr) 16 often in thin-section scale and even in single crystals. Two 17 amphibole populations were observed in the dacite: low-Al 18 hornblendes represent a cold (\800°C) silicic crystal 19 mush, whereas the high-Al pargasites crystallized in a hot 20 ([900°C) mafic magma. Amphibole thermobarometry 21 suggests that the silicic crystal mush was stored in an upper 22 crustal storage (*8-12 km). This was also the place where 23 the erupted dacitic magma was formed during the remo-24 bilization of upper crustal silicic crystal mush body by hot Author Proof We investigate the implications of our study for using 91 amphibole to constrain the subvolcanic plumbing systems 92 of andesitic to dacitic arc volcanoes in general. Finally, we 93 discuss the origin, conditions, and processes lead to com-94 monly observed bimodal amphibole populations in inter-95 mediate mixed magmas erupted at composite arc 96 volcanoes. Our study highlights that different amphibole 97 thermobarometers can produce essentially different results, 98 which may lead to false interpretations on the magma 99 evolution and architecture of the magma storage system 100 without clear textural control and crystal growth stratigra-101 phy. We point out the deficiency of the Ridolfi's thermo-102 barometric model that yields always the same p-T 103 evolution path for amphiboles along their stability curve. Geological setting105 Ciomadul volcano is located at the southeastern edge of the 106 Carpathian-Pannonian region, and this is the youngest 107 volcano of this area (Szakács and Seghedi 1995; Szakács 108 et al. 2002;Vinkler et al. 2007;Harangi et al. 2010; Kar-109 átson et al. 2013). It is found at the southern termination of 110 the Cȃlimani-Gurghiu-Harghita (CGH) andesitic-dacitic 111 volcanic chain (Fig. 1) 120 et al. 1987;Szakács et al. 1993; Mason et al. 1996). Vol-121 canic eruptions in Ciomadul could have started around 122 200 ka, and the last volcanic event occurred at 123 31,000 ± 260 cal BP. Initially, the volcanism was mostly 124 effusive and a lava dome complex developed called here 125 ''old Ciomadul.'' Later, the volcanic activity became more 126 explosive and as a result of successive phreatomagmatic 127 and subplinian eruptions, the edifice of the ''old Ciomadul'' 128 was partially destroyed and two deep explosive craters 129 were formed (Szakács and Seghedi 1995; Karátson et al. 130 2013). The erupted magma remained fairly homogeneous 131 through time and shows high-K dacitic composition (Sza-132 kács and Seghedi 1986; Vinkler et al. 1997). The geody-133 namic background of the CGH volcanism and particularly 134 the volcanic activity of southern Harghita and Ciomadul is 135 still hi...

The latest explosive eruptions of Ciomadul (Csomád) volcano, East Carpathians — A tephrostratigraphic approach for the 51–29 ka BP time interval

“…At Ciomadul, these magmas are considered -fairly homogenous‖ in composition through time by most authors (SiO 2 =63-68 wt%; K 2 O=3.0-3.5 wt%: Szakács and Seghedi, 1986;Vinkler et al, 2007;Kiss et al, 2014). However, Vinkler et al (2007) pointed out that the pumiceous pyroclastic sequence exposed at Băile Tuşnad (Tusnádfürdő; locality BTS hereafter; Fig.…”

“…Typical rocks of Ciomadul are porphyritic dacites, with a mineral assemblage consisting of plagioclase, amphibole and biotite, occasional clinopyroxene, orthopyroxene, quartz, K-feldspar and olivine, as well as accessory minerals of apatite, titanite, zircon and allanite (Jánosi, 1983;Szakács and Seghedi, 1986;Mason et al, 1996;Kiss et al, 2014).…”

A mineral and cumulate perspective to magma differentiation at Nisyros volcano, Aegean arc

“…Such magmas often display a bimodal distribution of amphibole compositions with a low-temperature population in equilibrium with the felsic host and a high-temperature population derived from the mafic recharge magma (Fig. 6; e.g., Coombs et al 2013;Kent 2014;Kiss et al 2014). Rare amphibole crystals in the HPRD (rhyo)dacites are resorbed and compositionally distinct from low-T amphibole but overlap with hightemperature compositions found in the enclaves, and thus appear to be derived from the mafic enclaves (Wyers and Barton 1989).…”

Neoproterozoic Rosetta Gabbro from northernmost Arabian–Nubian Shield, south Jordan: Geochemistry and petrogenesis

“…Cationic substitutions in amphiboles are temperature-sensitive as deduced from natural and experimental assemblages (e.g. Blundy and Holland, 1990;Holland and Blundy, 1994;Shane and Smith, 2013;Kiss et al, 2014). Shane and Smith (2013) concluded that nearly all of Al atomic substitutions in amphiboles can be accounted for by temperature-sensitive edenite and Ti tschermak exchange mechanisms with a minor role played by the pressure sensitive Al-tschermak substitution, consequently Alamphibole barometers can produce erroneous results.…”