Oceanic intraplate explosive eruptions fed directly from the mantle

Area of Science:

• Geochemistry and Volcanology
• Deep Earth Processes and Volatile Cycling

Background:

• Understanding magma volatile content is crucial for eruptive processes and deep Earth cycling, impacting planetary habitability.
• Previous research on magmatic volatiles has predominantly focused on subduction zones, with limited attention to intraplate volcanism and its global role.
• Mafic volcanoes, despite their abundance, are often underestimated for their explosive potential compared to silicic volcanoes.

Purpose of the Study:

• To investigate the volatile content and source of primitive magmas from Fogo volcano, Cabo Verde.
• To assess the role of oceanic intraplate mafic volcanism in global volatile cycles.
• To understand the mechanisms driving explosive eruptions in silica-undersaturated mafic systems.

Main Methods:

• Analysis of primitive melt inclusion (MI) data from Fogo volcano, focusing on host and melt major element compositions.
• Calculation of melt Mg# (Magnesium number) to identify primitive magma compositions.
• Determination of volatile concentrations (CO2, H2O, S, F, Cl) and oxidation state (NiNiO/NiNiO+1) in melt inclusions.

Main Results:

• Primitive melt inclusions from Fogo volcano (melt Mg# 70-71%) reveal oxidized and highly volatile-rich magmas.
• Volatile concentrations reach up to 2 wt% CO2, 2.8 wt% H2O, 6,000 ppm S, 1,900 ppm F, and 1,100 ppm Cl, classifying Fogo as a global endmember.
• Calculated magma storage depths indicate mantle origins (~20-30 km), with deep CO2 exsolution pressures up to ~800 MPa.

Conclusions:

• Oceanic intraplate explosive eruptions, exemplified by Fogo, sample volatile-rich mantle sources.
• High volatile concentrations, particularly CO2, inherited from the mantle source sustain these eruptions.
• Deep CO2 exsolution is the primary driver for magma ascent and explosivity in these systems, highlighting their significance in global volatile transport.