Eruptive history of the Late Quaternary Ciomadul (Csomád) volcano, East Carpathians, part I: timing of lava dome activity

Abstract

Located at the southern tip of the Intra-Carpathian Volcanic Range in Romania, and composed of a dozen dacitic lava domes, the Ciomadul (Csomád) volcanic complex is the youngest eruptive centre of the Carpatho-Pannonian Region. Whereas, in the last decade, the explosive history of Ciomadul since 50 ka has been well constrained by numerous studies, the chronology of the dome sequence still lacks robust chronological constraints and an extended analysis of all available data. Here, we apply a detailed K-Ar dating approach to refine the chronology of the lava dome eruptions, using the unspiked K-Ar Cassignol-Gillot technique. Our dating focused on the most voluminous central part of the lava dome complex. New eruption ages were determined following a strict separation (of 10 g) of groundmass from about 3 kg of unaltered sample rocks, thereby isolating material whose Manuscript Click here to access/download;Manuscript;Lahitte_BUVO-D-18-00067_R3.doc Click here to view linked References cooling was contemporaneous with the eruption. The newly applied methodology, mainly consisting of a double full preparation, first at larger grain size (~ 0.4 mm) and then at < 100 µm, provides an appropriate procedure to separate suitable material to obtain the K-Ar age of the eruption, i.e. the sample's groundmass, in which there is no risk of the presence of older, inherited crystals. Our new geochronological data set gives an improved insight into the temporal construction of the Ciomadul volcanic complex, where (due to the method applied here) all ages are younger than those from previous studies that used whole-rock K-Ar ages. Our new results show that Ciomadul's volcanic activity began with the construction of the southeastern, peripheral domes from ca. 850 ka to 440 ka. After a ca. 250 ky long repose period, the activity resumed in the northern part at around 200 ka, with subsequent domes emplaced between 200 and 130 ka, aligned roughly north-south in the westerncentral part of the complex. Following a 30 ky long quiescence period, the eastern-central domes formed between 100 and 60 ka. In addition to the chronological history of lava dome volcanism, we also investigated the sequence of crystallisation of mineral phases present in the lavas with respect to the modification of eruption ages. Ages obtained on pure minerals (plagioclase, amphibole and biotite) are systematically older than those obtained on groundmass, showing that most of them formed up to 1.85 Myr before eruption in a longlived, pre-Ciomadul magmatic system. Crystal size distributions (CSD) data support the age contrasts between juvenile groundmass and older inherited minerals. After injection of new magma and convective mixing with crystal clots, ascent of the resulting led to eruptions of material representing contrasting ages.

Geochronological evolution of the potentially active Iliniza Volcano (Ecuador) based on new K-Ar ages

“…Groundmass fraction is preferred for dating since it is the potassium-enriched phase that crystallizes last following the eruption, and thus incorporated the initial argon with atmospheric isotopic ratio. Furthermore, the use of groundmass avoids the possible contamination by inherited 40 Ar* contained in phenocrysts, which could skew ages in young volcanic products (e.g., Singer et al, 1998;Harford et al, 2002;Renne et al, 2012;Lahitte et al, 2019). Samples were prepared following the protocols detailed in Bablon et al (2018), where analytical procedures, standards used, and uncertainty calculations are also supplied.…”

The westernmost Late Miocene–Pliocene volcanic activity in the Vardar zone (North Macedonia)

“…The homogeneity and purity of the final fraction were checked under the binocular microscope. The prepared groundmass fractions of the volcanic rocks were then dated with the unspiked Cassignol-Gillot K-Ar technique (Cassignol and Gillot 1982;Gillot and Cornette 1986;Gillot et al 2006), which is wellsuited to date volcanic products over a wide time range with high precision (e.g., Samper et al 2007;Bablon et al 2018;Lahitte et al 2019;Dibacto et al 2020). Independent K and Ar measurements were performed on the separated, unaltered groundmass fractions in the Laboratoire GEOPS (Geosciences Paris-Saclay, Orsay, France).…”

“…At least two independent age determinations were realized for each sample and the final age is obtained as the mean of individual age determinations. The relative uncertainty on each determination is obtained as the quadratic sum of all independent sources of uncertainty, i.e., the K content (1%), the calibration of the mass spectrometer (1%), and the amount of radiogenic argon (e.g., Quidelleur et al 2001;Gillot et al 2006;Lahitte et al 2019). Ages are reported with 1σ level uncertainties in Table 1.…”

Fingerprinting the Late Pleistocene tephras of Ciomadul volcano, eastern–central Europe

“…2) in eastern-central Europe. It formed over the last 1 Myr with its last eruptions at around 30 ka (Vinkler et al, 2007;Harangi et al, 2010Harangi et al, , 2015Szakács et al, 2015;Karátson et al, 2016Karátson et al, , 2019Molnár et al, 2018Molnár et al, , 2019Lahitte et al, 2019). It is a volcanic complex, where volcanism started with intermittent lava dome extrusion events (1000-300 ka; Molnár et al, 2018).…”