Episodes of dormancy and eruption of the Late Pleistocene Ciomadul volcanic complex (Eastern Carpathians, Romania) constrained by zircon geochronology

Abstract

Ciomadul is the youngest volcanic system in the Carpathian-Pannonian Region recording eruptive activity from ca. 1 Ma to 30 ka. Based on combined zircon U-Th and (U-Th)/He geochronology, Ciomadul volcanism is divided into two main eruptive periods: Old Ciomadul (1 Ma-300 ka; OCEP) and Young Ciomadul Eruptive Period (160-30 ka; YCEP). OCEP activity comprises Eruptive Epochs 1-3, whereas new ages for eight lava domes and four pyroclastic units belonging to the YCEP lead to its further subdivision into two eruptive epochs: Eruptive Epochs 4 and 5. The extrusion of most of the lava domes occurred between 160 and 90 ka (Eruptive Epoch 4) during three eruptive episodes at ca. 155 ka, 135 ka and 95 ka (Eruptive Episodes 4/1, 4/ 2 and 4/3, respectively) along a NE-SW lineament, which is perpendicular to the regional NW-SE trend of the Călimani-Gurghiu-Harghita volcanic chain. Eruptive Epoch 5 occurred after a ca. 40 kyr of quiescence at ca. 55-30 ka, and is mainly characterized by explosive eruptions with a minor lava dome building activity. All of the dated pyroclastic outcrops, together with the lava dome of Piscul Pietros, belong to the older Eruptive Episode 5/1, with an eruption age of 55-45 ka. The eruption centers of Eruptive Epoch 5 are located at the junction of the conjugated NW-SE and NE-SW lineaments defined by the older eruptive centers. The whole-rock geochemistry of all studied samples is fairly homogeneous (SiO 2 = 63-69 wt%, K 2 O = 3-4 wt%). It also overlaps with the composition of the lava domes of the Old Ciomadul Eruptive Period, implying a monotonous geochemical characteristic for the past 1 Myr. The eruption rates for the Ciomadul volcanism were determined based on the erupted lava dome volume calculations, supplemented with the eruption ages. The activity peaked during the Eruptive Epoch 4 (160-90 ka), having an eruption rate of 0.1 km 3 /kyr. In comparison, these values are 0.05 km 3 /kyr for the YCEP (160-30 ka) and 0.01 km 3 /kyr for the overall Ciomadul volcanism (1 Ma-30 ka). Based on the geochemical characteristics, the quiescence periods and the lifetime of the complex, as well as the relatively small amount of erupted material, this volcanic system can be placed in a subduction-related post-collisional geodynamic setting, which shows strong chemical similarities to continental arc volcanism. The commonly found long repose times between the active phases suggest that the nature of a volcano cannot be understood solely based on the elapsed time since the last eruption. Instead, comprehensive geochronology, coupled with the understanding of the magma storage behavior could be a base of hazard assessment for volcanic fields, where the last eruptions occurred several 10's of thousand years ago and therefore they are not considered as potentially active.

Noble Gas and Carbon Isotope Systematics at the Seemingly Inactive Ciomadul Volcano (Eastern‐Central Europe, Romania): Evidence for Volcanic Degassing

“…The last eruption in Ciomadul occurred 30 ka (Harangi et al, 2010;Molnár et al, 2019), yet there is an intense CO 2 degassing with a minimum flux of 8.7 × 10 3 t/year (Kis et al, Geochemistry, Geophysics, Geosystems In addition, previous investigations (Althaus et al, 2000;Vaselli et al, 2002;Túri et al, 2016) highlighted the outgassing of mantle-derived volatiles at Ciomadul volcano. He isotopic ratios in the fluids collected in this study are up to 3.1 R a similar to those obtained from previous studies (Figure 4 and Table 3).…”

“…It is part of a postcollisional volcanic belt, which comprises a series of andesitic to dacitic volcanoes, developed parallel with the Carpathian orogeny. Ciomadul is part of a lava dome field and this central volcanic complex involves 8-14 km 3 of high-K dacitic lavas (Karátson & Timár, 2005;Molnár et al, 2019;Szakács et al, 2015). Ciomadul is part of a lava dome field and this central volcanic complex involves 8-14 km 3 of high-K dacitic lavas (Karátson & Timár, 2005;Molnár et al, 2019;Szakács et al, 2015).…”

“…This central volcano is surrounded by further isolated lava domes (Baba Laposa, Haramul Mic, Dealul Mare, Büdös-Puturosul and Bálványos; Molnár et al, 2018, Figure 2). Volcanism at the Ciomadul volcanic dome field started around 1 Ma, while the most voluminous Ciomadul volcanic structure has developed over the last approximately 160 kyr (Molnár et al, , 2019. During the first volcanic stage, the intermittent lava dome extrusions were separated by relatively long dormant periods even exceeding 100 kyr.…”

“…Volcanism at the Ciomadul volcanic dome field started around 1 Ma, while the most voluminous Ciomadul volcanic structure has developed over the last approximately 160 kyr (Molnár et al, , 2019. The second volcanic stage was characterized by initial lava dome effusion and then, after approximately 40 kyr of quiescence, a more explosive volcanic activity occurred (from 57 to 30 ka, Harangi et al, 2010;Karátson et al, 2016;Molnár et al, 2018Molnár et al, , 2019Moriya et al, 1995Moriya et al, , 1996Vinkler et al, 2007). The second volcanic stage was characterized by initial lava dome effusion and then, after approximately 40 kyr of quiescence, a more explosive volcanic activity occurred (from 57 to 30 ka, Harangi et al, 2010;Karátson et al, 2016;Molnár et al, 2018Molnár et al, , 2019Moriya et al, 1995Moriya et al, , 1996Vinkler et al, 2007).…”

“…The Ciomadul dacites have U and Th concentrations of 3 and 15 ppm, respectively (Molnár et al, , 2019Vinkler et al, 2007). Thus, the primary magmas of Ciomadul could be also characterized by such isotope ratio.…”