Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
Browse
15 results
Search Results
Item 40Ar/39Ar geochronology of Neogene phreatomagmatic volcanism 3 in the western Pannonian Basin, Hungary(Elsevier, 2007) Németh, Károly; Wijbrans, Jan; Martin, Ulrike; Balogh, KadosaNeogene alkaline basaltic volcanic fields in the western Pannonian Basin, Hungary, including the Bakony–Balaton Highland and the Little Hungarian Plain volcanic fields are the erosional remnants of clusters of small-volume, possibly monogenetic volcanoes. Moderately to strongly eroded maars, tuff rings, scoria cones, and associated lava flows span an age range of ca. 6 Myr as previously determined by the K/Ar method. High resolution 40Ar/39Ar plateau ages on 18 samples have been obtained to determine the age range for the western Pannonian Basin Neogene intracontinental volcanic province. The new 40Ar/39Ar age determinations confirm the previously obtained K/Ar ages in the sense that no systematic biases were found between the two data sets. However, our study also serves to illustrate the inherent advantages of the 40Ar/39Ar technique: greater analytical precision, and internal tests for reliability of the obtained results provide more stringent constraints on reconstructions of the magmatic evolution of the volcanic field. Periods of increased activity with multiple eruptions occurred at ca. 7.95 Ma, 4.10 Ma, 3.80 Ma and 3.00 Ma. These new results more precisely date remnants of lava lakes or flows that define geomorphological marker horizons, for which the age is significant for interpreting the erosion history of the landscape. The results also demonstrate that during short periods of more intense activity not only were new centers formed but pre-existing centers were rejuvenated.Item 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, GaborAbstract 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.Item Understanding the evolution of maar craters(Massey University., 2006-01-01) Haller, Miguel J.; de Wall, Helga; Martin, Ulrike; Nemeth, KarolyNo abstract availableItem 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, GaborThe 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.Item Influence of titanomagnetite composition on the magnetic anisotropy in a dyke-sill complex in Hungary(Massey University., 2006-01-01) Renk, Danny; de Wall, Helga; Martin, Ulrike; Nemeth, KarolyIn the last decades low-field magnetic susceptibility measurements have become an increasingly attractive method for geological studies which use the scalar values (bulk susceptibility) as well as the directional information, the anisotropy of magnetic susceptibility (AMS). Because of the potential for detecting weak fabric anisotropies, AMS has become a routine method for assessing flow directions in magmatic bodies. Sources of AMS in ferrimagnetic basaltic rocks are mainly titanomagnetites. After Jackson et al. (1998) and de Wall (2000), the magnetic susceptibility (MS) of titanomagnetite varies strongly with mineral composition and is in the low-field range strongly depending on the field amplitude of the inducing magnetic field. Here we present a systematic study to record the effects of field dependence on AMS of dykes, sills and lava flows. Variation in MS characteristics have been found indicative for lava emplacement and flow dynamics (Cañón-Tapia et al. 1997, Cañón-Tapia & Pinkerton 2000). The contribution of the effect of field dependence on MS and AMS in titanomagnetite-bearing volcanic rocks needs to be assessed for a reliable interpretation of AMS variations. The key study has been carried out at the Ság-hegy volcanic complex in the Little Hungarian Plain. It is composed of a phreatomagmatic tuff ring, formed during the pliocene-miocene period. After meteoric water supply ended, the phreatomagmatic eruptive style changed into an effusive behaviour and the tephra ring was filled with a lava lake and a dyke-sill complex transected the pyroclastic successions. We report AMS characteristics of sills, dykes and lavas from the lake interior and outflowing lava deposits. Furthermore we discriminated samples that represent the transition from dykes to sills and from intrusive (dyke) to effusive (lava flow) emplacement, respectively. The MS has been measured by a KLY-4S kappabridge (AGICO, Brno) which allows a record of the AMS at a high sensitivity and in various field amplitudes (2 to 450 A/m).Item MAAR conference in Hungary(Massey University., 2005-01-01) Martin, Ulrike; Nemeth, KarolyNo abstract availableItem Mio/Pliocene phreatomagmatic volcanism in the Western Pannonian Basin(Massey University., 2004-01-01) Martin, Ulrike; Nemeth, KarolyNo abstract availableItem 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, UlrikeNo abstract availableItem Quaternary phreatomagmatic volcanoes of southern Tenerife, Spain: Montana Pelada tuff ring and Caldera del Rey Maar.(Massey University., 2004-01-01) Martin, Ulrike; Nemeth, KarolyNo abstract availableItem Interaction between lava lakes and pyroclastic sequences in phreatomagmatic volcanoes: Haláp and Badacsony, Western Hungary.(Massey University., 2002-01-01) Martin, Ulrike; Nemeth, KarolyNo abstract available