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An Upper Pliocene coarse pumice breccia generated by a shallow submarine explosive eruption, Milos, Greece

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Stewart, AL and McPhie, J (2004) An Upper Pliocene coarse pumice breccia generated by a shallow submarine explosive eruption, Milos, Greece. Bulletin of Volcanology, 66 (1). pp. 15-28. ISSN 0258-8900

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Abstract

The Filakopi Pumice Breccia (FPB) is a very
well exposed, Pliocene volcaniclastic unit on Milos,
Greece, and has a minimum bulk volume of 1 km3. It
consists of three main units: (A) basal lithic breccia (4–
8 m) mainly composed of angular to subangular, andesitic
and dacitic clasts up to 2.6 m in diameter; (B) very thickly
bedded, poorly sorted pumice breccia (16–17 m); and (C)
very thick, reversely graded, grain-supported, coarse
pumice breccia (6.5–20 m), at the top. The depositional
setting is well constrained as shallow marine (up to a few
hundred metres) by overlying fossiliferous and bioturbated
mudstone. This large volume of fine pumice clasts is
interpreted to be the product of an explosive eruption
from a submarine vent because: (1) pumice clasts are the
dominant component; (2) the coarse pumice clasts
(>64 mm) have complete quenched margins; (3) very
large (>1 m) pumice clasts are common; (4) overall, the
formation shows good hydraulic sorting; and (5) a
significant volume of ash was deposited together with
the coarsest pyroclasts.
The bed forms in units A and B suggest deposition
from lithic-rich and pumiceous, respectively, submarine
gravity currents. In unit C, the coarse (up to 6.5 m)
pumice clasts are set in matrix that grades upwards from
diffusely stratified, fine (1–2 cm) pumice clasts at the
base to laminated shard rich mud at the top. The coarse
pumice clasts in unit C were settled from suspension and
the framework was progressively infilled by fine pumice
clasts from waning traction currents and then by watersettled ash. The FPB displays important features of the
products of submarine explosive eruptions that result
from the ambient fluid being seawater, rather than volcanic gas or air. In particular, submarine pyroclastic
deposits are characterised by the presence of very coarse
juvenile pumice clasts, pumice clasts with complete
quenched rims, and good hydraulic sorting.

Item Type: Article
Keywords: Submarine explosive eruption, Volcaniclastic succession, Coarse rhyolitic pumice, Gravity currents, Suspension, Coarse lithic breccia
Journal or Publication Title: Bulletin of Volcanology
Page Range: pp. 15-28
ISSN: 0258-8900
Identification Number - DOI: 10.1007/s00445-003-0292-z
Additional Information:

The original publication is available at www.springerlink.com

Date Deposited: 09 Oct 2007 16:49
Last Modified: 18 Nov 2014 03:22
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