Iblean diatremes 3: volcanic processes on a Miocene carbonate platform (Iblean Mountains, SE-Sicily): a comparison of deep vs. shallow marine eruptive processes

Abstract

Evolution and magma fragmentation processes of two contrasting, well-exposed diatreme complexes interbedded with Late Miocene calcareous marine sediments in distinct sedimentary environments of a carbonate platform (Iblean Plateau, Sicily) are compared with each other. The nephelinitic Cozzo Molino diatreme (CMD) to the east developed in shallow water (0-80 m water depth); the alkali basaltic Valle Guffari seamount (VGS) to the west grew on a deeper water carbonate ramp (150-200 m water depth). We focus on the dominant boundary conditions inferred to have governed depth of magma fragmentation and subaqueous emplacement mechanisms: water depth, physical nature of host rocks, magma composition, and inferred differences in initial volatile concentrations. There are gross similarities in the composition of the two moderately evolved magmas. The low-viscosity magmas in both diatremes were laden with xenoliths originating from mantle to lower crustal sites. Although similar, the eastern shallow water CMD was likely more volatile-rich, with magma fragmented prior to reaching the surface and the surrounding tephra cone was partly emergent. The eruptions of the entirely submarine VGS diatreme complex in the deeper water environment were dominated by interaction of soft sediment and alkali basaltic magma or a pre-fragmented volatile-particle mixture. Eruption columns were, thus, strongly damped and the submarine complex never pierced the water surface.

The architecture of submarine monogenetic volcanoes – insights from 3D seismic data

“…Similar feeder relationships are inferred beneath other submarine volcanoes (e.g. Suiting & Schmincke, ). Since there are few sills within the dataset, we infer that dykes formed the dominant mechanism of magma transport to the paleosurface.…”

Geochemistry and eruptive behaviour of the Finca la Nava maar volcano (Campo de Calatrava, south-central Spain)

“…magmatic fragmentation (Clement 1982;Stoppa 1996;Field and Scott Smith 1998;Sparks et al 2006;Wilson and Head III 2007;Cas et al 2008;Mattsson and Tripoli 2011;Berghuijs and Mattsson 2013)]. This latter hypothesis is usually applied to silica-undersaturated, CO 2 -rich, magma compositions such as kimberlites, carbonatites, melilitites and nephelinites rising quickly from the mantle to the surface (Sparks et al 2006;Brown et al 2009;Suiting and Schmincke 2009;Mattsson and Tripoli 2011;Suiting and Schmincke 2012). Furthermore, an often observed phenomenon is the drying out of the eruption due to the decrease in water supply, which leads to a shift of the mode of fragmentation from a phreatomagmatic to a magmatic one (Lorenz 1986;Németh et al 2001;Geshi et al 2011).…”