Journal Articles

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Lepusztult maar/diatrema szerkezetek a Bakony-Balaton Felvidék Vulkáni Területröl (Eroded maar/diatrema structures from the Bakony-Balaton Highland Volcanic Field).
(Massey University., 2003-01-01) Nemeth, Karoly; Martin, Ulrike; Csillag, Gabor
The Bakony - Balaton Highland Voclanic Field (BBHVF) is a Late Miocene/Pliocene alkaline basaltic intraplate monogenetic volcanic field comprises variable eroded maars, tuff rings, cinder cones and valley-ponded lavaflows/fields. Large volcanic edifices are relatively well studied in volcanological point of view but smaller occurrences of pyroclastic rocks have not yet been dealt with at Bakony - Balaton Highland Voclanic Field. However, their presence could give a good reference for erosion rate calculations of the syn-volcanic (Pliocene) landscape and develop better understanding of the eruption mechanism of phreatomagmatic volcanoes. Five, small volume pyroclastic rock occurrences have been mapped and studied. Each of these pyroclastic rock locations are ellipsoid in plane and seems to exhibit angular contact with the pre-volcanic rock units. The identified pyroclastic rocks are predominantly lapilli tuffs and minor pyroclastic breccias. They are rich in accidental lithic fragments picked up from the former conduit wall-forming rock units. All of the lapilli tuffs are rich in juvenile fragments. Juvenile fragments are both tachylite and sideromelane glass shards, indicative for variable degree of magma/water interaction as well as variable travelling time through air by the clasts. The two major types of juvenile fragments are 1) clear, light yellow, slightly microvesicular, and microcrystalline sideromelane glass shard and 2) strongly oriented, textured, trachytic textured, dark colour, slightly vesicular lava, and/or tachylite glass shards. The presence of this type of juvenile fragments, especially the presence of sideromelane, suggests sudden cooling and fragmentation of the intruding melt due to phreatomagmatic magma/water interaction. The composition of the volcanic glass shards is predominantly tephrite, phonotephrite (light colour, chilled, microlite-poor shards) or trachybasalt (trachytic texture, microlite-rich shards). However, the composition and texture of the glass shards are often affected by variable degree of palagonitization, which proccess clearly occurs in larger glass shards, leaving intact only the interior of the shards, and creating darker yellow rim around the glass shard. The glass shards, both sideromelane and tachylite, contain a large number of entrapped sedimentary clasts, vesicle-filling xenoliths. These xenoliths are both 1) pre-volcanic fluvio-lacustrine, shallow marine silts, sand or mud and 2) pyroclastic unit-derived fragments. Their presence marks the importance of the interaction and possible pre-mixing prior to phreatomagmatic fragmentation and disruption of the bedrocks by the intruding alkaline basaltic magma and water-rich slurry. The slurry is inferred to be a volcanic conduit-filling mixture of fluvio-lacustrine/shallow marine siliciclastic and pyroclastic debris, rich in water from different sources, such as ground-water, valley floor occupied swamp, creek, or small lake water. The lapilli tuffs contain both shallow-level pre-volcanic and deep-level basement rock fragments, indicating that the explosion locus migrated during eruption and sampled a thick section of the pre-volcanic rock units. Sedimentary clasts are common from the immediate pre-volcanic rock unit (Pannonian sand), regardless that they are already eroded in the areas or just represented by thin veneers. This finding suggests that these sediments were widespread in syn-volcanic time. Based on the textural characteristics, field relationships and the micro-textures of the studied pyroclastic rock exposures, they are interpreted to be deeply eroded sub-surface structures of phreatomagmatic volcanoes. According to the unsorted, chaotic features of these pyroclastic rocks, they are inferred to be exposed lower diatremes. Steeply dipping beds of near-vent base surge and air-fall beds interpreted to be collapsed and later subsided blocks of crater-rim deposits.
Interaction between lava lakes and pyroclastic sequences in phreatomagmatic volcanoes: HalÃ¡p and Badacsony, Western Hungary.
(Massey University., 2002-01-01) Martin, Ulrike; Nemeth, Karoly
No abstract available
High level sill and dyke intrusions initiated from rapidly buried mafic lava flows in scoria cones of Tongoa, Vanuatu (New Hebrides), South Pacific
(Massey University., 2006-01-01) Nemeth, Karoly; White, James D. L.
Scoria cones are generally considered to grow rapidly in days to weeks or months. During their growth lava flows may be fed onto the cone surface from lava-lake breaches, or form by coalescence of spatter; such flows are preserved interbedded with scoria lapilli and ash beds. On Tongoa, an island of the Vanuatu volcanic arc in the South Pacific, a series of scoria cones developed during the Holocene, forming a widespread monogenetic volcanic field. Half sections of scoria cones along the coast expose complex interior architecture cone architectures. On the western side of Tongoa Island a scoria cone remnant with steeply crater-ward dipping beds of scoria ash and lapilli contains various dm-to-m thick lava flows, which are connected by irregular dikes cutting obliquely across the beds of the cone. The lava flows are coherent igneous bodies with well-developed flow top and basal breccias. The lavas interbedded with the cone-forming layers are part of a larger (up to 7 m thick) body that is connected to dykes and sills of irregular geometries that intrude the cone's pyroclastic layers. This 3D relationship suggests that the lava flows were buried quickly under the accumulating scoriaceous deposits. This allowed subsequent escape of magma from the fluid interiors of flows, with the magma then squeezed upward or laterally into the accumulating pyroclastic pile. Movement of the pile above the partly mobile lava, and potential destabilisation during intrusion into the pile of lava squeezed from the flows, may signal the onset of localised cone failures, and could be implicated in development of major cone breaches (e.g. Paricutin).
Subaqueous volcanism and their depositional processes, their relationship to subaerial volcanism: review
(Massey University., 1999-01-01) Nemeth, Karoly
A vizalatti vulkanizmus jelenségei és üledékképződési folyamatai, kapcsolatai a szárazföldi vulkáni folyamatokkal: attekintes (Subaqueous volcanism and their depositional processes, their relationship to subaerial volcanism: review)
Peperites and soft sediment deformation textures of a shallow subaqueous Miocene rhyolitic cryptodome and dyke complex, Pálháza, Hungary
(Massey University., 2006-01-01) Nemeth, Karoly; Pecskay, Zoltan; Martin, Ulrike; Gmeling, Katalin; Molnar, Ferenc; Cronin, Shane J.
Miocene rhyolitic shallow intrusions, cryptodomes and domes emplaced into soft, wet sediment in shallow subaqueous environment form a large intrusive complex in the NE side of the Tokaj Mts. at Pálháza in NE-Hungary. The intrusive complex show interaction textures with the host sediment where blocky peperites formed in a dm-scale, however, irregular contacts closely resembling globular mega-peperites are prominent in the tens of metres scale. The more than 200 m thick succession of intrusive complex interpreted to be a generally steadily growing shallow dyke, cryptodome, and dome complex in a shallow subaqueous environment, similar to those reported from Ponza, Italy.

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