Browsing by Author "Csillag, Gabor"

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    Depositional record of a Pliocene nested multivent maar complex at Fekete-hegy, Pannonian Basin, western Hungary.
    (Massey University., 2002-01-01) Martin, Ulrike; Nemeth, Karoly; Auer, Andreas; Breitkreutz, Christoph; Csillag, Gabor
    No abstract available
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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.
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    Pitfalls in erosion level calculation based on remnants of maar and diatreme volcanoes (Les pièges de la reconstitution des topographies d'érosion initiales fondée sur les vestiges des maars et diatrèmes volcaniques)
    (Massey University., 2007-01-01) Nemeth, Karoly; Martin, Ulrike; Csillag, Gabor
    Abstract Erosion estimates based on geometrical dimension measurements of eroded maar/diatreme volcanoes are useful methods to determine syn-volcanic surface level and syn-volcanic bedrock stratigraphy. However, such considerations on volcanic architecture should only be employed as a first-order approach to determine the state of erosion. We demonstrate, on both young and eroded maar/diatreme volcanoes, that establishing the volcanic facies architecture gives vital information on the environment in which the volcano erupted. In 'soft' rocks, maar volcanoes are broad and underlain by 'champagne glass'-shaped diatremes. In contrast, the crater wall of maar volcanoes that erupted through "hard rocks" will be steep, filled with lacustrine volcaniclastic deposits and underlain by deep diatremes. Résumé L'estimation de l'érosion fondée sur la géométrie des volcans de type maar-diatrème est une méthode applicable à la reconstruction de la surface syn-volcanique et de la stratigraphie de la série sous-jacente. Toutefois les considérations relatives à l'architecture volcanique doivent seulement être utilisées comme une première approche pour déterminer le niveau initial de la surface aujourd'hui érodée. Nous démontrons que la détermination des faciès volcaniques, tant dans les maars-diatrèmes récents que dans les systèmes érodés de ce type, donne des informations fondamentales sur la nature des roches encaissantes au sein desquelles l'éruption volcanique s'est produite. Dans les roches encaissantes meubles, les maars sont larges avec un diatrème sous-jacent en forme de « coupe de champagne». Au contraire, au sein de roches plus résistantes, les cratères de maars sont entourés de parois raides et bien souvent remplis de dépôts lacustres d'origine volcanoclastique qui masquent des diatrèmes profonds.
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    Pliocene crater lake deposits and soft sediment deformation structures associated with a phreatomagmatic volcano, Pula maar, western Hungary.
    (Massey University., 2002-01-01) Nemeth, Karoly; Martin, Ulrike; Csillag, Gabor
    No abstract available