Paleovolcanological reconstruction of the Vepor andesite stratovolcano (Central Slovakia)

In the region of the Hercynian crystalline massive of the Veporic unit (East of the Central Slovakia Volcanic Field, CSVF) denudation remnants of the intrusive-extrusive bodies and volcanoclastic rocks of supposed Neogene age have already been identified in the past. Paleovolcanological reconstruction has been done of former extensive andesite volcano, later removed by intensive erosion, on the basis of the recent mapping (in the scale 1:3 000 – 1: 10 000), petrological and radiometric data.
   The region of central volcanic zone is exposed by deep denudation cut around the Magnetový vrch hill. The subvolcanic multi-stage diorite intrusion-pluton of cedar shape (K-Ar age:12.08 ±0.47 and 12.28 ±0.42 Ma, respectively) in its lower part in the valley at the level of the Rimavica river (500 m altitude) steeply intrudes into the complex of the Hercynian granite and metamorphic rocks. On the western margin the intrusion transforms into several sub-horizontal apophyses emplaced in form of the sills along the lithological boundary between Hercynian granite and Middle Triassic limestone and dolomite and higher within the Mesozoic complex (Magnetový vrch hill, 960 m altitude). Zones of magnetite scarns are evolved at the contact of carbonates with the diorite intrusion. The intrusion is later crosscut by dyke swarm of W-E to ENE-WSW direction. The dykes (K-Ar age: 11.94 ±1.0 Ma) are mostly formed by coarse grained amphibole hyperstene andesite porphyry. Dyke swarm of basaltic andesite to basalt (K-Ar age: 12.02 ±1.05 Ma) of ENE-WSW orientation at the SW slope of the Magnetový Vrch hill is most probably related to small parasitic volcano.
   Proximal volcanic zone. Deeper levels of the complex of intrusive-extrusive bodies of hyperstene amphibole andesites ±garnet (K-Ar age: 12.10 ±0.38 Ma) characterised by autometamorphic alteration are exposed by erosion. Direction of steep fan-like lineation (fluidality) and zones with autoclastic breccias near the margins indicate forms of dome-type alternatively tholoide-type. Another small-sized of amphibole andesites (K-Ar age: 12.25 ±0.5 Ma) to rhyodacites (K-Ar age: 12.53 ±0.42 Ma) in the northern part of the proximal zone confirms the presence of small parasitic volcanoes in the region of the former volcanic slope. One small parasitic volcano that survived denudation represented by volcanic neck and adjacent remnant of cinder cone (agglutinate pyroclastic deposits) was found.
   Distal volcanic zone of the Vepor stratovolcano is represented by denudation remnants of the volcanoclastic rocks that filled former paleo-valleys (canyons) of radial orientation with respect to central volcanic zone. More extensive remnant of NW-SE orientation is the Hajna Hora hill complex located on the NW from the proximal zone. A study of the paleovalley filling formed by pyroclastic and epiclastic volcanic rocks (block-and-ash flows, ashpumice flows and lahars) alternating with layers of epiclastic volcanic sandstones and conglomerates enable reconstruction of eruptive cycles and volcanic events. The filling of another radial paleo-valley on the west from the central volcanic zone represented by erosion relict of the lava flow of pyroxene andesite (K-Ar age: 11.56 ±0.43 Ma) of WSW orientation cover the peak area of the Klenovsky Vepor hill. The lava flow overlaid basal fluvial sediments. Pokorádz complex, formed by volcanoclastic and volcanosedimentary rocks, is located SE from central volcanic zone. Deposition of the volcanic material took place in the shallow fluvial-limnic environment. Tuffitic-sandy sedimentation with conglomerate layers was episodically interrupted by a mass transport in the form of gravitational flows, lahars and block-and-ash flows.
   On the basis of the field observations and K-Ar data it is possible to reconstruct the complex succession of the volcanic and intrusive events of the Vepor stratovolcano. The KAr ages suggest that the stratovolcano was active for a relatively short time during Lower Sarmatian, between 12.53 – 11.56 Ma. The radiometric ages are in a good agreement with biostratigraphic data.
   Acknowledgment: This work was supported by the project 16 06 supported by Ministry of Environment of Slovak Republic and by the Slovak Research and Development Agency under the contract No. APVV-0549-07. This work was also supported by the OTKA grant (Hungarian Scientific Foundation) K68153.