Emplacement history of a low-viscosity, fountain-fed pantelleritic lava flow

Stevenson, Richard J.; Briggs, R. M.; Hodder, A. P. W.

doi:10.1016/0377-0273(93)90030-u

Cited by 34 publications

(35 citation statements)

References 32 publications

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“…To document textural variation throughout the exposed thickness of the Ben Lomond flow, the following physical parameters were measured: density, porosity, void aspect ratio, spherulite size, and microlite length, following the methods described in Stevenson et al (1993 information, together with the superposition of textures, can be used to document the sequence of events during the emplacement of the lava flow. For all textural parameters, measurements were taken from the top, middle, and base of each unit to be fully representative of any textural variation within each unit.…”

Section: Methodsmentioning

confidence: 99%

Physical volcanology and emplacement history of the Ben Lomond rhyolite lava flow, Taupo Volcanic Centre, New Zealand

Stevenson

Briggs

Hodder

1994

New Zealand Journal of Geology and Geophysics

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Currently, there are two contrasting models concerning the state in which rhyolite lava reaches the surface: (1) the permeable foam model, where the lava reaches the surface as an expanded foam and collapses into dense obsidian during lava flow; and (2) the traditional model, where decreased load pressure leads to vesiculation of the upper surface of the dome.In order to test these models, textural parameters were documented on outcrops of the Ben Lomond rhyolite dome, which has two flow lobes comprising an eroded dome (c. 100 ka old) cut by the Whangamata Fault. A composite stratigraphy of the upper 60 m of the flow, assembled from three sections (roadcut, airstrip and fault scarp), comprises, irom the flow top: finely vesicular pumice, black aphyric obsidian, and a spherulitic transition zone above a central crystalline rhyolite core. An explosion breccia occurs as a pod at a depth of c. 35 m and cross-cuts the upper two units us an inverted cone-shaped deposit-an infilled explosion pit.Eight physical parameters (density and porosity, void aspect ratios, spherulite size and proportion, microlite size and abundance, and volatile contents) were measured throughout the exposed thickness of the flow. Results show that primary vesicles-those that deform pre-existing flow banding-are most numerous within the finely vesicular pumice layer but are suppressed c. 10-15 m below the surface. Vesicularity and volatile contents are anomalously high in explosion breccia fabrics. Furthermore, microlites are ubiquitous in the flow but absent in the explosion breccia. Incomplete degassing of the ascending magma took place, resulting in volatiles being distributed within the flow thickness during lava emplacement. The lava flow carapace revesiculated during extrusion (primary vesiculation), whereas secondary vesiculation (spherulites and lithophysae) was associated with groundmass crystallisation of the flow centre, causing localised volatile enrichments responsible ior the formation of explosion breccias. An emplacement model, formulated for the Ben Lomond dome, shows that

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Section: Methodsmentioning

confidence: 99%

Physical volcanology and emplacement history of the Ben Lomond rhyolite lava flow, Taupo Volcanic Centre, New Zealand

Stevenson

Briggs

Hodder

1994

New Zealand Journal of Geology and Geophysics

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“…There are many possible mechanisms of magmatic banding, including magma segregation (Onikiyenko 1970), convection and fractionation in the magma reservoir (Geshi 1999;Weinberg et al 2001;Barbey et al 2008), magma fragmentation and then welding owing to the large shear rate of flowing magma (see Stevenson et al 1993;Smith 1996;Gonnermann & Manga 2005), shearing of mingled magma in turbulent flow (Seaman 1995;Perugini et al 2003a,b), repetition of fracturing and healing during magma ascent within a volcanic conduit (Tuffen et al 2003;Rust et al 2004), magma cooling inward from the contacts (Huppert & Sparks 1989), and so forth. In the study case, the banding is generally considered as a product of magma mingling (R. F. Weinberg, personal communication).…”

Section: Origin Of Magmatic Bandingmentioning

confidence: 99%

The diversity of flow structures in felsic dykes

Tian

Shan

2011

JGS

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Numerous structures and textures, which can be related to magma flow, were observed in felsic dykes intruding late Mesozoic granitoid plutons in the Jiaodong peninsula, in eastern Shandong province, eastern China. These flow structures may be classified into two categories, interior and peripheral. The former group includes magmatic bands, various types of folds (e.g. injection, sheath, similar and disharmonic folds), rotation of phenocrysts, magmatic foliation or lineation, and crenulation, whereas the latter includes hot tool marks and quarrying structures. Magmatic banding resulted from shearing of mingled magma during magma flow in the dykes. The magma seemed to flow rapidly, probably triggering turbulence in some thick dykes. Interaction at the contact between the hot, moving magma and the cold, stationary wallrock sometimes produced the peripheral structures. A few measurements of hot tool marks and of magmatic lineation reveal a roughly horizontal flow of magma within these dykes. For the dominant NE-SW-striking dyke set in the Laoshan granitoid pluton, the felsic magma probably ascended on or to the SW of the pluton to feed the dyke swarm, and then flowed laterally to drive the horizontal propagation of dykes.

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“…These eruption styles have been attributed to the high viscosity of silicic magma. However, in some cases, silicic magma has been interpreted as erupting and behaving as low viscosity magma, such as basaltic magma (e.g., Stevenson et al, 1993) and the products are interpreted as spatter deposits and rheomorphic pyroclastic deposits (terminology after . In general, spatter is produced by strombolian and Hawaiian style fountaining events and deposits are characterized by fountain-fed (clastogenic) lavas and spatter cones and ramparts such as 1986 eruption of Izu-Oshima volcano (Sumner, 1998).…”

Section: Introductionmentioning

confidence: 99%

Eruption and emplacement of the Yamakogawa Rhyolite in central Kyushu, Japan: A model for emplacement of rhyolitic spatter

Furukawa

Kamata

2014

Earth Planet Sp

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The Yamakogawa Rhyolite, which erupted in the early Quaternary period in central Kyushu, Japan, comprises seven units, three contain of which spatter and stretched pumice. Our fieldwork shows that these are the deposits of strombolian fire-fountains and rheomorphic tuff. Such deposits derived from silicic magma have been previously described and still are controversial. Some of the reasons given for their formation were exclusively peralkaline composition and high-magmatic temperature. The chemical analyses of the Yamakogawa Rhyolite show nonperalkaline composition and low-magmatic temperature. Moreover, the mineral assemblage of the Yamakogawa Rhyolite suggests that its water content was indistinguishable from other rhyolitic deposits. This is the first report that demonstrates that eruption of silicic magma as fire-fountain and pyroclastic flow with rheomorphism is not, necessarily, restricted to peralkaline composition, high-magmatic temperature and low-water content rhyolite.

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Emplacement history of a low-viscosity, fountain-fed pantelleritic lava flow

Cited by 34 publications

References 32 publications

Physical volcanology and emplacement history of the Ben Lomond rhyolite lava flow, Taupo Volcanic Centre, New Zealand

Physical volcanology and emplacement history of the Ben Lomond rhyolite lava flow, Taupo Volcanic Centre, New Zealand

The diversity of flow structures in felsic dykes

Eruption and emplacement of the Yamakogawa Rhyolite in central Kyushu, Japan: A model for emplacement of rhyolitic spatter

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