Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
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Item 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 VIIn 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.Item Deltaic density currents and turbidity deposits related to maar crater rims and their importance for palaeogeographic reconstruction of the Bakony-Balaton Highland Volcanic Field, Hungary(Massey University., 2001) Nemeth KThe Bakony-Balaton Highland Volcanic Field (BBHVF), active in the late Miocene, is located in the Central Pannonian Basin and consists of around 100 mostly alkaline basaltic eruptive centers. After volcanism, lake deposition took place inside the maar craters. Above the primary volcaniclastic deposits, thick maar-lake volcaniclastic sediments occur. The steeply dipping (25-35o), 25-30 cm thick, coarse-grained, inverse-to-normal graded beds of reworked tuff represent the foresets of large Gilbert-delta fronts built into the maar crater lakes of the BBHVF. The coarse-grained beds were deposited by low-density granule debris flows and grain flows. 10-15 cm thick beds of fine-grained, cross-bedded reworked volcaniclastic sandstone and mudstone beds are interbedded, probably deposited by turbulent sediment gravity flows. The delta fronts usually indicate transportation from north to south, suggesting a strong north-south trending fluvial system, active during or, shortly after volcanism in the BBHVF. The juvenile fragments of the deltaic sediments are often highly vesiculated, rounded/semirounded glassy lapilli. These suggest that the maar volcanism was related to widespread Strombolian-type explosive volcanism after the maar-forming phreatomagmatic events. Deposits derived from scoria cones were easily washed into the steep walled maar basins and deposited by debris flows into the maar lakes.