Journal Articles

Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915

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Subject: search.filters.subject.Diatreme

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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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    Cenozoic diatreme field in Chubut (Argentina) as evidence of phreatomagmatic volcanism accompanied with extensive Patagonian plateau basalt volcanism?
    (International Union of Geological Sciences, 2007) Nemeth K; Martin U; Haller MJ; Alric VI
    In Patagonia, Argentina, at the northern border of the Patagonian Cenozoic mafic plateau lava fields, newly discovered diatremes stand about 100 m above the surrounding plain. These diatremes document phreatomagmatic episodes associated with the formation of the volcanic fields. The identified pyroclastic and intrusive rocks are exposed lower diatremes of former phreatomagmatic volcanoes and their feeding dyke systems. These remotely located erosional remnants cut through Paleozoic granitoids and Jurassic/Cretaceous alternating siliciclastic continental successions that are relatively easily eroded. Plateau lava fields are generally located a few hundreds of metres above the highest level of the present tops of the preserved diatremes suggesting a complex erosional history and potential interrelationships between the newly identified diatremes and the surrounding lava fields. Uprising magma from the underlying feeder dyke into the diatreme root zone intruded the clastic debris in the diatremes, inflated them and mingled with the debris to form subterranean peperite. The significance of identifying diatremes in Patagonia are twofold: 1) in the syn-eruptive paleoenvironment, water was available in various "soft-sediments", commonly porous, media aquifer sources, and 2) the identified abundant diatremes that form diatreme fields are good source candidates for the extensive lava fields with phreatomagmatism facilitating magma rise with effective opening of fissures before major lava effusions.
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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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    Large hydrovolcanic field in the Pannonian Basin: general characteristics of the Bakony- Balaton Highland Volcanic Field, Hungary.
    (Massey University., 1999-01-01) Nemeth, Karoly; Martin, Ulrike
    No abstract available
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    Eroded porous-media aquifer controlled hydrovolcanic centers in the South Lake Balaton region, Hungary: The Boglar volcano
    (Akad�miai Kiad�, 1999) Nemeth K; Martin U; Philippe M
    The volcanic centers next to Balatonboglar township represent 3.5 Ma old products of post-extensional alkaline basaltic volcanism in the Pannonian Basin (eastern Central Europe). They are small, eroded volcanic centers located on the southern shore of Lake Balaton and genetically related to the Bakony-Balaton Highland Volcanic Field eruptive centers. The relatively small area (500 m x 500 m) contains at least 2 eruptive centers, which are probably related to each other and have built up a complex volcano, called the Boglar Volcano. The volcanic rocks overlie the older Pannonian clastic sedimentary sequence and represent the topographic highs in this area. The areas of lower elevation around the eruptive centers are covered by Pleistocene to Holocene swamp, lake and river clastic sediments, which strongly suggest intense erosion during the last few million years. All volcanic rocks around Balatonboglar are volcaniclastic. There is no evidence of lava flow occurrence. The volcaniclastic sediments have been divided into two lithofacies associations. The largest amount of volcaniclastic rocks is located in the center of the local hills and has been interpreted as a phreatomagmatic crater fill lapilli tuff. They contain large amphibole megacrysts and small olivine crystals. The second lithofacies association is interpreted as lahar deposits. This sequence contains an unusually large amount of fossil tree trunks, which are identified as Abies species. Within a small area in the western hills small outcrops show evidence of maar-lake clastic sediment occurrence. On the hilltops debris shows intimate interaction processes between clastic sediments and basaltic melt. We interpret this to mean that the eruptive centers of Boglar Volcano were formed under subaerial conditions, with explosions fueled by intensive interaction between water-saturated Pannonian sand and uprising basaltic magma.