Kolumbo submarine volcano (Greece): An active window into the Aegean subduction system

Abstract

Submarine volcanism represents ~80% of the volcanic activity on Earth and is an important source of mantle-derived gases. These gases are of basic importance for the comprehension of mantle characteristics in areas where subaerial volcanism is missing or strongly modified by the presence of crustal/atmospheric components. Though, the study of submarine volcanism remains a challenge due to their hazardousness and sea-depth. Here, we report 3He/4He measurements in CO2–dominated gases discharged at 500 m below sea level from the high-temperature (~220 °C) hydrothermal system of the Kolumbo submarine volcano (Greece), located 7 km northeast off Santorini Island in the central part of the Hellenic Volcanic Arc (HVA). We highlight that the mantle below Kolumbo and Santorini has a 3He/4He signature of at least 7.0 Ra (being Ra the 3He/4He ratio of atmospheric He equal to 1.39×10−6), 3 Ra units higher than actually known for gases-rocks from Santorini. This ratio is also the highest measured across the HVA and is indicative of the direct degassing of a Mid-Ocean-Ridge-Basalts (MORB)-like mantle through lithospheric faults. We finally highlight that the degassing of high-temperature fluids with a MORB-like 3He/4He ratio corroborates a vigorous outgassing of mantle-derived volatiles with potential hazard at the Kolumbo submarine volcano.

Breathing modes of Kolumbo submarine volcano (Santorini, Greece)

“…1). These observations are in complete agreement with other sets of data and visual observations258.…”

“…In that aspect, an exploration campaign in 2010 and 2011 focused –among other things– on the intense vent activity and the continuous exchange of gases and hydrothermal fluids. In the water column, important anomalies in temperature and conductivity depth profiles were also recorded5678. Detailed investigation of the vent activity of a submarine volcano is usually performed in terms of the study of the 3 He/ 4 He ratio, as this is one of the most powerful geochemical tracers to define the origin of volatiles released from the solid earth and the magmatic/mantle features.…”

Volatile contents of mafic-to-intermediate magmas at San Cristóbal volcano in Nicaragua

“…13b). The few measurements made in FI from other volcanoes as well as most of the measurements in fumarole gases show 3 He/ 4 He within the MORB range, as also observed in several other arc volcanoes (Hilton et al, 2002;Di Piazza et al, 2015;Rizzo et al, 2016). This implies that the variable sediment input from the subducting slab (highlighted by Ba/La) and the extent of mantle melting do not involve 4 He-bearing rocks.…”

A distinct source and differentiation history for Kolumbo submarine volcano, Santorini volcanic field, Aegean arc

“…Hence, it is highly unlikely that the 1650 AD pumice are derived from the same shallow magmatic system from which the Kameni dacites are tapped. This is supported by the distinct He isotope composition of gasses emitted from vents in the Kameni islands and the Kolumbo hydrothermal system (3–4 Ra and 7.0–7.1 Ra, respectively) [ Rizzo et al ., ]. A scenario in which the 1650 AD pumices represent evolved residual magma of the 3.6 ka rhyodacitic Minoan eruption can also be precluded on the basis of large trace element and isotope differences (Figures and ).…”