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Pillow lava and spasmodic submarine fire fountaining in the middle Miocene marginal basin, Sado Island, Japan


Fujibayashi, N and Asakura, K and Hattori, T and Allen, S, Pillow lava and spasmodic submarine fire fountaining in the middle Miocene marginal basin, Sado Island, Japan, Island Arc, 23, (4) pp. 344-364. ISSN 1038-4871 (2014) [Refereed Article]

Copyright Statement

Copyright 2014 Wiley Publishing Asia Pty Ltd

DOI: doi:10.1111/iar.12091


The Sawasaki basalt unit of the Ogi Basalt Member is a middle Miocene submarine volcano formed in a marginal basin, cropping out on the coast of the Ogi Peninsula, Sado Island, Japan. It is approx. 100 m thick, more than 4 km wide, and is composed of pillow lavas (Sawasaki pillow lava) and overlying fire fountain deposits (Sawasaki pyroclastic rocks). The Sawasaki pillow lava is a pile of nearly-horizontal lava flows. Massive sheet lavas and lava pods grade into pillow lavas. The flat surfaces of the sheet lavas suggest that they spread over a summit plain. The margin of the Sawasaki pillow lava is dominated by thin elongated pillow lobes (2030 cm across) dipping at 4560, contrast with the large pillows (40100 cm across) in the core. The proximal lithofacies of the Sawasaki pyroclastic rocks is scoria agglomerate which is composed of tens of stratified beds. Individual beds have a range of clast sizes and abundance of subaqueous bombs (sometimes up to >70%), which suggests that they were formed by submarine spasmodic fire fountain eruptions. Progressive aggradation from a turbulent flow allowed settling of well-preserved fluidal-shaped subaqueous bombs in a fines-depleted matrix. The basal layer shows lamina, scour and imbrication of scoria clasts. The thick scoria agglomerate beds with large subaqueous bombs, derived from energetic fire fountains, were emplaced during transition to higher degrees of hydrovolcanic fragmentation. Alternating scoria lapilli tuff and tuff beds in the distal area may represent the coupled topset and foreset beds formed by deposition from dilute, turbulent flows, and cascading of volcanic debris from the crest of the volcanic hill.

Item Details

Item Type:Refereed Article
Keywords:back-arc basin, basalt, Ogi Basalt, pillow lava, Sawasaki basalt, scoria agglomerate, spasmodic fire fountain, submarine explosive eruption, submarine volcanic hill
Research Division:Earth Sciences
Research Group:Geology
Research Field:Volcanology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Allen, S (Dr Sharon Allen)
ID Code:98512
Year Published:2014
Web of Science® Times Cited:3
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2015-02-18
Last Modified:2017-11-02

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