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Complex variations during a caldera-forming Plinian eruption, including precursor deposits, thick pumice fallout, co-ignimbrite breccias and climactic lag breccias: The 184 ka Lower Pumice 1 eruption sequence, Santorini, Greece
Citation
Simmons, JM and Cas, RAF and Druitt, TH and Folkes, CB, Complex variations during a caldera-forming Plinian eruption, including precursor deposits, thick pumice fallout, co-ignimbrite breccias and climactic lag breccias: The 184 ka Lower Pumice 1 eruption sequence, Santorini, Greece, Journal of Volcanology and Geothermal Research, 324 pp. 200-219. ISSN 0377-0273 (2016) [Refereed Article]
Copyright Statement
Copyright 2016 Elsevier B.V.
DOI: doi:10.1016/j.jvolgeores.2016.05.013
Abstract
The 184 ka Lower Pumice 1 eruption sequence records a complex history of
eruption behaviours denoted by two significant eruptive phases: (1) a
minor precursor (LP1-Pc) and (2) a major Plinian phase (LP1-A, B, C).
The precursor phase produced 13 small-volume pyroclastic fallout, surge
and flow deposits, which record the transition from a dominantly
magmatic to a phreatomagmatic eruptive style, and exhibit a normal
(dacite to andesitic-dacite) to reverse (andesitic-dacite to dacite)
compositional zonation of juvenile pyroclasts in the stratigraphy.
Incipient bioturbation and variability in unit thickness and lithology
reflect multiple time breaks and highlight the episodic nature of
volcanism prior to the main Plinian eruption phase. The Plinian magmatic
eruption phase is defined by three major stratigraphic divisions,
including a basal pumice fallout deposit (LP1-A), an overlying
valley-confined ignimbrite (LP1-B) and a compositionally zoned
(rhyodacite to basaltic andesite) lithic-rich lag breccia (LP1-C), which
caps the sequence. This sequence records the initial development of a
buoyant convective eruption column and the transition to eruption column
and catastrophic late-stage caldera collapse events. Similarities in
pyroclast properties (i.e., chemistry, density), between the Plinian
fallout (LP1-A) and pyroclastic flow (LP1-B) deposits, indicate that
changes in magma properties exerted no influence on the dynamics and
temporal evolution of the LP1 eruption. Conversely, lithic breccias at
the base of the LP1-B ignimbrite suggest that the transition from a
buoyant convective column to column collapse was facilitated by
mechanical erosion of the conduit system and/or the initiation of
caldera collapse, leading to vent widening, an increase in magma
discharge rate and the increased incorporation of lithics into the
eruption column, causing mass overload. Lithic-rich lag breccia deposits
(LP1-C), which cap the eruption sequence, record incremental,
high-energy caldera collapse events, whereby downfaulting occurred in
discrete jumps, resulting in variable magma discharge rates and the
development of a fissure vent system.
Item Details
Item Type: | Refereed Article |
---|---|
Keywords: | Lower Pumice 1 (LP1), Santorini caldera, precursory eruption, Plinian eruption, ignimbrite, collapse breccias |
Research Division: | Earth Sciences |
Research Group: | Geology |
Research Field: | Volcanology |
Objective Division: | Energy |
Objective Group: | Energy exploration |
Objective Field: | Geothermal exploration |
UTAS Author: | Cas, RAF (Professor Ray Cas) |
ID Code: | 115234 |
Year Published: | 2016 |
Web of Science® Times Cited: | 17 |
Deposited By: | Earth Sciences |
Deposited On: | 2017-03-10 |
Last Modified: | 2017-11-02 |
Downloads: | 0 |
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