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The Youngest Volcanic Eruptions in East‐ FEATURE Feature The youngest volcanic eruptions in East- Central Europe—new findings from the Ciomadul lava dome complex, East Carpathians, Romania D. Karátson1, D. Veres2, S. Wulf3,4, 5 Violent explosive eruptions occurred between c. 51 and 29 thousand years R. Gertisser , E. ago—during the Last Glacial Maximum in East-Central Europe—at the Magyari6 & M. picturesque volcano of Ciomadul, located at the southernmost tip of the Inner Bormann7 Carpathian Volcanic Range in Romania. Field volcanology, glass geochemistry 1Eötvös University, Department of Physical of tephra, radiocarbon and optically stimulated luminescene dating, along Geography, Pázmány s. with coring the lacustrine infill of the two explosive craters of Ciomadul (St 1/C, H-1117 Budapest, Ana and Mohos), constrain the last volcanic activity to three subsequent Hungary eruptive stages. The explosivity was due to the silicic composition of the [email protected] 2 magma producing Plinian-style eruptions, and the interaction of magma Institute of Speleology, Romanian Academy, with the underlying, water-rich rocks resulting in violent phreatomagmatic Clinicilor 5, 400006 Cluj- outbursts. Tephra (volcanic ash) from these eruptions are interbedded with Napoca, Romania; 3GFZ contemporaneous loess deposits, which form thick sequences in the vicinity German Research Centre of the volcano. Moreover, tephra layers are also preserved in the older for Geosciences, Section Mohos crater infill, providing an important archive for palaeoclimate studies. 5.2 – Climate Dynamics and Landscape Evolution, Identifying the final phreatomagmatic eruption of Ciomadul at c. 29.6 ka, Telegrafenberg, D-14473 which shaped the present-day landform of the 1600-m-wide St Ana explosion Potsdam, Germany; crater, we were able to correlate related tephra deposits as far as 350 km 4Heidelberg University, from the source within a thick loess-palaeosol sequence at the Dniester Institute of Earth Sciences, Im Neuenheimer Feld Delta in Roxolany, Ukraine. A refined tephrostratigraphy, based on a number 234, D-69120 Heidelberg, of newly found exposures in the Ciomadul surrounding region as well as Germany; 5Keele University, correlation with the distal terrestrial and marine (e.g. Black Sea) volcano- School of Physical and sedimentary record, is expected from ongoing studies. Geographical Sciences, Keele, ST5 5BG, UK; 6Eötvös University, MTA- The Carpathian Basin, or geologically speaking twentieth century and recently discovered dinosaur MTM-ELTE Research Group the Carpatho-Pannonian Region (CPR), is not fossil finds in Transylvania (Romania) and the Bakony for Paleontology, Pázmány particularly well known for its volcanic activity. Mountains (Hungary), respectively, are more obvious s. 1/C, H-1117 Budapest, From a geological point of view, its valuable rare pieces of international recognition. In addition, the Hungary; 7 University of minerals (several of which were described in the torsion balance developed by the physicist Baron Cologne, Institute of eighteenth century from volcanic mountains), the Loránd Eötvös (1848–1919), which measured small Geography Education, unusual rock assemblage of the Ditrău Massif in the variations in gravity, should also be mentioned as Gronewaldstrasse 2, East Carpathians (which inspired A. Streckeisen for it provided a tool for exploration geophysicists to D-50931 Cologne, his famous petrographic classification), or the early discover the deep structure of the Carpathian Basin. Germany 60 © John Wiley & Sons Ltd, The Geologists’ Association & The Geological Society of London, Geology Today, Vol. 33, No. 2, March–April 2017 FEATURE (a) (b) The vicinity of Lake Balaton in Hungary, located rhyolite and dacite tuff sheets (mostly ignimbrites) Fig. 1. Tectonic and in the western part of the CPR, is amongst the best of Miocene age were also formed throughout the geographical setting of Ciomadul known examples of volcanic activity within the CPR. basin, resulting from colossal explosive eruptions in volcano (left) within the East Several tens of volcanic centres constitute the Bakony– extensional settings. However, with a few exceptions, Carpathian Volcanic Range (in Balaton Upland Volcanic Field that consists of maars, these latter formations have been subsided in the past red); volcanological sketch map tuff rings and amazing basalt buttes (e.g. Badacsony millions of years beneath the sedimentary infill of the (right). Figure simplified from Hill). However, in contrast to these and other Hungarian Plain and also in Transylvania due to syn- Karátson et al. (2016) after many authors. predominantly Pliocene to Early Pleistocene alkali and post-rift phases of basin formation. basaltic igneous centres, which are volumetrically The plate tectonic interpretation of this superb but insignificant and scattered throughout the basin as extinct volcanic activity is rather complex, almost to monogenetic fields, there is an almost continuous, the same extent as that of Italy. Apart from the alkali much more voluminuous Inner Carpathian Volcanic basalts that resemble the peri-Alpine occurrences of Range. This range extends from the Northwest to deep mantle origin, there is a strong calc-alkaline the East Carpathians through present-day Slovakia, character of many volcanic fields, indicating Hungary, Ukraine, and Romania. The c. 650 km-long contemporaneous or inherited subduction. The CPR chain of volcanic mountains, up to 1500–2000 m in consists of two continental micro-plates, the so-called elevation, was active from Miocene to latest Pleistocene Alpine-Carpathian-Pannonian ‘ALCAPA’ and the times. Associated, intense hydrothermal ore Tisza-Dacia, which moved to their present position mineralisation produced rich gold and silver reserves due to the closure of the Tethys by the northward (e.g. Telkibánya in North Hungary) which were used pushing African plate. As a result, subduction of for coinage in medieval times. In addition, extensive land-locked oceanic basins, collision along the Fig. 2. View of the Ciomadul lava dome complex from the north. © John Wiley & Sons Ltd, The Geologists’ Association & The Geological Society of London, Geology Today, Vol. 33, No. 2, March–April 2017 61 FEATURE orogen, and extension in internal (e.g. back-arc) areas were responsible for triggering the above- mentioned wide variety of Neogene to Quaternary volcanism. The youngest volcanic segment of the CPR extends along the inner side of the East Carpathians (Fig. 1), from the northern Călimani to the southern Harghita Mountains, where typical calc-alkaline, intermediate (mostly andesitic) volcanic activity shows a well-defined age progression from 10 million to 30 thousand years ago. This atypical along-arc migration of volcanism has been interpreted as a result of oblique subduction that forced the zone of magma genesis to move progressively southward. Ciomadul: Late Pleistocene explosive activity within the past 50 ky The youngest volcanic activity within the East Carpathians, and that of the entire CPR, occurred at the very end of the arc at Ciomadul (or with its original Hungarian name, Csomád) volcano (Fig. 2). At the chain terminus of South Harghita, this biotite, and occasional clinopyroxene, orthopyroxene, Fig. 3. Fresh dacite of touristic, pine-forest covered mountain is a complex quartz, K-feldspar and olivine. Geochemically, the Ciomadul’s lava dome rock. of scattered or superimposed 1000–1300 m high dacites belong to the potassium-rich rocks of the lava domes rather than a single volcanic edifice. The South Harghita volcanic segment. highest, amalgamated part of the volcano (1301 m Showing a ‘youthful’ morphology and being rich at Ciomadul Mare) hosts scenic twin craters—lake St in gas emanations (mofettes), the relatively young Ana and Mohos peat bog—the formation of which is age of the volcano was already noticed in the past interpreted as truncating a central dome complex by centuries. Modern stratigraphic studies based on late-stage explosive eruptions. The rim of the eastern sedimentary relationships verified this view, but Mohos crater as well as the southern flanks of St reliable age constraints for an unambigously Late Ana crater are mostly composed of unconsolidated Pleistocene activity have only been provided in the era volcaniclastic, mostly pyroclastic deposits (volcanic of radiometric dating. It turned out that, subsequent ash and pumice). to predominantly effusive lava dome activity, the Ciomadul’s rock type is porphyritic dacite (Fig. 3), last, mostly explosive eruptions of Ciomadul occurred with a mineral assemblage of plagioclase, amphibole, within the past c. 50 ky. Such young volcanism, rather unique in Central Europe, has attracted a (a) (b) Fig. 4. Outcrops showing pyroclastic units from the latest explosive eruptions of Ciomadul. a. A proximal gully at the outlet of Mohos crater reveals thick pyroclastic layers overlain by volcano-sedimentary and lacustrine successions. Inset in the lower left corner shows large grain size and poor sorting of clasts from the lowermost ‘M3’ pumiceous block-and-ash flow deposit, related to explosive lava dome destruction. b. Erosional gully at a medial distance from the source with well-preserved pyroclastic-flow and -surge units, overlain by the latest c. 29.6 ka phreatomagmatic tephra. 62 © John Wiley & Sons Ltd, The Geologists’ Association & The Geological Society of London, Geology Today, Vol. 33, No. 2, March–April 2017 FEATURE growing interest by geoscientists, and, in the past decade, a number of international research teams
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