Determining clast and magnetic fabric of a subaqueous lahar deposit as a tool for reconstructing paleoflow directions and emplacement processes.

Flow-related fabric of a subaqueously emplaced laharic deposit (Rám Hill Pumiceous Sandstone) were investigated around the middle Miocene Keserűs Hill lava dome group (northern Hungary). A twofold methodology, consisting of image analyis on rock surfaces and low-field anisotropy of magnetic susceptibility (AMS), was used to determine large-scale flow paths and emplacement processes. In addition, comparative measurements of magnetic anisotropy were performed by using an MFK1-FA multifunction kappabridge with 3D rotator (Studynka et al. 2014) at Agico, Inc. (Brno, Czech Republic). The results indicate a very good agreement between the azimuths of a-axis of the most elongated clasts from image analysis and the orientation of K1 susceptibilities from the measurements of the two laboratories. This agreement of fabric direction obtained by the two different methods allows to draw the following implications: 1) Fabric direction-derived large-scale flow paths show a near-radial pattern around the proposed eruption centre (Karátson et al. 2007) of the Keserűs Hill lava dome group (Fig. 1). Thus, our new data on paleoflow directions quantitatively confirm the former, one central vent-dominated volcano-structural reconstruction which was proposed on the basis of facies analysis. 2) Aggradation from multiple lahar pulses is presumable due to the vertical variation of shear direction within the exposures

Vulkanológiai kutatások az észak-magyarországi andezitvulkáni hegységekben = Volcanological research in the North Hungarian andesite volcanic mountains

A kutatómunka az észak-magyarországi vulkáni hegységekben korábban - más OTKA- és FKFP-pályázatok, valamint nemzetközi együttműködések segítségével - megkezdett vulkanológiai és vulkángeomorfológiai vizsgálatok folytatására, összegzésére irányult. Súlypontja a Visegrádi-hegység vulkanizmusának és a Dunakanyar - részben ezzel kapcsolatos - felszínfejlődésének a kutatása volt, emellett kutatómunkát végeztünk a Mátra középső és keleti részén, és összehasonlító tanulmányokat folytattunk az Eperjes-Tokaji-hegységben és a Keleti-Kárpátok vulkáni vonulatában. A pályázatban résztvevő, illetve a publikációkban társszerző kutatók a földtudomány igen különböző területeit képviselték, így a munka során sokféle módszert tudtunk alkalmazni (terepi vulkanológia, morfometria, DEM-elemzés, K/Ar-kormeghatározás, paleomágneses vizsgálatok, őslénytan stb.). A kutatómunka eredményeként eddig 11 publikáció jelent meg/áll megjelenés alatt, ebből 5 nemzetközi folyóiratban, 3 nemzetközi, 1 hazai konferencián, valamint 2 könyvfejezet formájában. | This research has continued the volcanological and volcanic geomorphological investigations that were initiated in the North Hungarian volcanic mountains supported by other OTKA and FKFP projects as well as international cooperations. Its main focus was the volcanism of the Visegrád Mountains and its relationship to the relief evolution of its northern foreground - the Danube Bend -; further research was done in the Mátra Mountains, and comparative studies were made in the Tokaj-Eperjes(Slánské) as well as East Carpathian volcanic mountains. The participating researchers and other co-authors of the project represented various aspects of earth sciences. As a consequence, many independent methods have been applied during the research, e.g. field volcanology, morphometry, DEM analysis, K/Ar geochronology, paleomagnetic investigations, paleontology etc. As a result, 11 publications have been or about to be published so far, out of this 5 articles in international journals, 4 presentations in conferences (3 in international forums, 1 in Hungary), and 2 book chapters

Egy összetett alsó-miocén piroklasztit sorozat Észak-Magyarországról: az alsó-riolittufa vulkanoszedimentológiája: A complex Lower Miocene pyroclastic succession in Northern Hungary: volcanic sedimentology of the Lower Rhyolite Tuff

The volcaniclastics of the lower rhyolite tuff in the Nógrád Basin (near Nemti) and in the Western Bükk Foreland (near Ostoros) preserve a complex explosive volcanic history. Although the two successions exhibit similar complexity, they are rather different. Hence, a layer-based physical volcanological investigation of the lower rhyolite tuff was required in order to better constrain on its usefulness as a marker horizon and to localize the vents which produced this pyroclastic complex

Egy összetett kitörési eseménysorozat nyomai a Bükkalján (Észak-Magyarország): a Kács Egység: Signs of complex eruption events at the Bükk Foreland (Northern-Hungary): the Kács Member

A stratified, complex volcanic succession occuring at Kács (Bükk Foreland Volcanic Area, Northern-Hungary) belonging to the Lower Pyroclastic Complex was documented in detail in this work. The tephra-generating volcanic processes were inferred based on the volcanological and granulometric features of the deposits as follows: at least three Plinian eruptions (I-III) produced fallout tephra separated by paleosol horizons recording inter-eruptive quiescence periods. Several features of the earliest eruption sequence suggest a phreatomagmatic eruption style. Regional correlation attempts are supported by paleomagnetic rotation data, which helped the classification of the sequence right below to the Middle Pyroclastic Complex

A Miocene Phreatoplinian eruption in the North-Eastern Pannonian Basin, Hungary: The Jató Member

A Middle Miocene, ~8 m thick pyroclastic succession, reported from the Bükk Foreland Volcanic Area (BFVA) in Northern Hungary (Central Europe) specified here as the Jató Member, was produced by silicic phreatomagmatism (Phreatoplinian sensu lato). Two well-preserved outcrops ~8 km apart and inferred to be within ~10–50 km from source represent the discontinuously exposed, layered, paleosol-bounded, phreatomagmatic JatóMember. They show an identical phenocrystal assemblage of feldspar, biotite and amphibole without weathered zones or signs of erosion, that suggest deposition in one eruption phase lasting hours to months. The succession contains three subunits: 1) subunit A, 1.8 m thick, a series of well-sorted fine to coarse ash or lapilli tuff layers with constant thickness; 2) subunit B, 2.1 m thick, a series of normal-graded layers with an upper fine-grained zone containing abundant ash aggregates with a coarser-grained core and distinctively finer-grained outer rim; 3) subunit C, 4.5 m thick, a massive, poorly to well-sorted coarse ash with gas escape structures and ash aggregates at its base. The upward change of these lithofacies implies an initially sustained dry fallout-dominated deposition of ash and pumice lapilli resulting in subunit A. Subsequently, multiple wet and dilute Pyroclastic Density Currents (PDCs) dispersed subunits B and C. The general abundance of PDC-related ash aggregates in the middle-upper part of the succession (particularly in subunit B), and the transformation of a fall-dominated to a collapsing depositional regime producing wet dilute PDCs, imply the increasing influence of water during the eruption (Phreatoplinian sensu lato). The presence of water is related to an epicontinental sea duringMiddle to LateMiocene in the Carpatho-Pannonian region. The transition from an initial dry magmatic phase generated fallout activity followed by the emplacement of wet PDCs' rich in ash aggregates, when external water infiltrated from a surrounding lake or sea water entered the vent.ÚNKP-16-3 New National Excellence Program of the Ministry of Human Capacities and the National Talent Program – Young Talents of the Nation (NTPNFTÖ- 18-B-0130). Thisworkwas supported by theHungarian Scientific Research Fund project nos. K105245, K115472, K128625, K131894, K128122 and by the European Union and the State of Hungary, cofinanced by the European Regional Development Fund in the project of GINOP - 2.3.2 - 15 - 2016 - 00009 ICER. KN's contribution and field work were possible by the fund available under the Erasmus+ International Credit Mobility, - ELTE –Massey University Research Cooperation Program. Balázs Bradák acknowledges the financial support of project BU235P18 (Junta de Castilla y León, Spain) and the European Regional Development Fund (ERD)