caa a22 4500 386402183 CHVBK 20180307112204.0 cr unu---uuuuu 161130e198903 xx s 000 0 eng 10.1017/S0016756800006270 doi S0016756800006270 pii (NATIONALLICENCE)cambridge-10.1017/S0016756800006270 Explosive volcanism on Santorini, Greece [Elektronische Daten] Santorini volcanic field has had 12 major (1-10 km3 or more of magma), and numerous minor, explosive eruptions over the last ~ 200 ka. Deposits from these eruptions (Thera Pyroclastic Formation) are well exposed in caldera-wall successions up to 200 m thick. Each of the major eruptions began with a pumice-fall phase, and most culminated with emplacement of pyroclastic flows. Pyroclastic flows of at least six eruptions deposited proximal lag deposits exposed widely in the caldera wall. The lag deposits include coarse-grained lithic breccias (andesitic to rhyodacitic eruptions) and spatter agglomerates (andesitic eruptions only). Facies associations between lithic breccia, spatter agglomerate, and ignimbrite from the same eruption can be very complex. For some eruptions, lag deposits provide the only evidence for pyroclastic flows, because most of the ignimbrite is buried on the lower flanks of Santorini or under the sea. At least eight eruptions tapped compositionally heterogeneous magma chambers, producing deposits with a range of zoning patterns and compositional gaps. Three eruptions display a silicic-silicic + mafic-silicic zoning not previously reported. Four eruptions vented large volumes of dacitic or rhyodacitic pumice, and may account for 90% or more of all silicic magma discharged from Santorini. The Thera Pyroclastic Formation and coeval lavas record two major mafic-to-silicic cycles of Santorini volcanism. Each cycle commenced with explosive eruptions of andesite or dacite, accompanied by construction of composite shields and stratocones, and culminated in a pair of major dacitic or rhyodacitic eruptions. Sequences of scoria and ash deposits occur between most of the twelve major members and record repeated stratocone or shield construction following a large explosive eruption. Volcanism at Santorini has focussed on a deep NE-SW basement fracture, which has acted as a pathway for magma ascent. At least four major explosive eruptions began at a vent complex on this fracture. Composite volcanoes constructed north of the fracture were dissected by at least three caldera-collapse events associated with the pyroclastic eruptions. Southern Santorini consists of pryoclastic ejecta draped over a pre-volcanic island and a ridge of early- to mid-Pleistocene volcanics. The southern half of the present-day caldera basin is a long-lived, essentially non-volcanic, depression, defined by topographic highs to the south and east, but deepened by subsidence associated with the main northern caldera complex, and is probably not a separate caldera. Copyright © Cambridge University Press 1989 Druitt T. H. Department of Geology, University of Wales, P.O. Box 914, Cardiff CF1 3YE, U.K. Mellors R. A. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K.. Pyle D. M. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K.. Sparks R. S. J. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K.. Geological Magazine Cambridge University Press 126/2(1989-03), 95-126 0016-7568 126:2<95 1989 126 GEO https://doi.org/10.1017/S0016756800006270 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S0016756800006270 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Druitt T. H. Department of Geology, University of Wales, P.O. Box 914, Cardiff CF1 3YE, U.K NATIONALLICENCE 700 1- Mellors R. A. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K NATIONALLICENCE 700 1- Pyle D. M. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K NATIONALLICENCE 700 1- Sparks R. S. J. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K NATIONALLICENCE 773 0- Geological Magazine Cambridge University Press 126/2(1989-03), 95-126 0016-7568 126:2<95 1989 126 GEO CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge