Large volume phreatomagmatic ignimbrites from the Colli Albani volcano (Middle Pleistocene, Italy)

摘要: Abstract In this paper we describe four large volume, ash- and accretionary lapilli-rich, phreatomagmatic compound ignimbrite units, mafic in composition, from Colli Albani volcano, south of Rome. The that form the ‘Pisolitic Tuffs’ succession, are separated by paleosols represent earliest explosive volume eruptive episodes Quaternary Alban Hills volcano. occurrence phreatomagmatic–phreatoplinian eruptions implies availability quantities water interacting with rising magma. paleogeography area below volcano has been reconstructed analysis stratigraphic data more than a thousand bore-holes distributed around allowed to identify NW-trending NE-trending paleotopographic lows underlie central interpreted as extensional tectonic basins. These filled Lower Middle Pleistocene, pre-volcanic lacustrine fluvial deposits suggest at least part volcanic hosted lake or lagoon. absence sedimentary xenoliths Pisolitic Tuffs low vesicularity scoria shards interacted poorly fragmented magma very shallow level, triggering explosivity eruptions. We was mostly surficial related presence lagoon lake. environment, it is likely vents were subaqueous allowing continuous access conduit. Considering minimum calculated products for succession >37 km3 each eruption unit averages approximately 10 km3, caldera collapse, which would have persistence Taupo-like phreatoplinian activity. After last eruption, however, fragmentation style ignimbrites became magmatic, suggesting extinction after date. Each units show basal fallout overlain complex association aspect ratio surge ignimbrites. Phreatomagmatic pyroclastic flow found distances 40 km important facies variation according paleotopography. To west flows reached Tyrrhenian coast emplaced stratified on flat topography, reflect both spreading an unconfined topography their interaction areas. By contrast, east where confined within paleovalleys, main thick massive.