A carbon-rich lithospheric mantle as a source for the large CO2 emissions of Etna volcano (Italy)

Alessandro Bragagni,Riccardo Avanzinelli,Carsten Münker,Filippo Mastroianni,Sandro Conticelli

doi:10.1130/g49510.1

Abstract

Abstract Etna volcano in Italy releases an exceptional amount of CO2 (9083 t/day) and contributes to 10% of global volcanic emission. The reasons for its extreme CO2 degassing are not yet understood. Using high-precision high field strength element (HFSE) concentrations in magmas from volcanoes in southern Italy, we show that the high Nb/Ta of Etna (up to 26) reveals a mantle source affected by carbonatite metasomatism, which is likely responsible for the large CO2 fluxes. As observed at Etna, carbon-rich mantle domains influence CO2 degassing also outside of continental rifts and therefore play a fundamental role in explaining volcanic CO2 fluxes in different geodynamic settings. Collectively, our study demonstrates that HFSE ratios in magmatic rocks are viable tracers for volcanic carbon degassing that can be used to study present-day settings and, possibly, past emissions.

Highlights

INTRODUCTIONVolcanism represents the main input for atmospheric CO2. The highly heterogeneous CO2 flux of present-day volcanoes testifies to the presence of multiple sources, which must be identified to infer longterm variations in CO2 fluxes
Over geological time, volcanism represents the main input for atmospheric CO2
Etna volcano in Italy releases an exceptional amount of CO2 (9083 t/day) and contributes to 10% of global volcanic emission

Summary

INTRODUCTION

Volcanism represents the main input for atmospheric CO2. The highly heterogeneous CO2 flux of present-day volcanoes testifies to the presence of multiple sources, which must be identified to infer longterm variations in CO2 fluxes. Because Etna is located between oceanic and continental lithosphere, it is plausible that carbon-rich SCLM metasomatism influences the CO2 degassing of Etna To evaluate this possibility, we report high-precision concentrations of high field strength elements (HFSE) that have been demonstrated to be sensitive to carbonatite metasomatism (e.g., Green, 1995; Pfänder et al, 2012). The OIB-like Nb/Ta of Pantelleria indicates that the high Nb/Ta is not a common feature of the regional asthenosphere, but affects only Etna and Monte Vulture These two volcanoes share a peculiar tectonic setting, being on the opposite edges of the subducting Ionian slab. Because mantle domains affected by carbonatite-like metasomatism can contain carbon on the order of few weight percent (Foley and Fischer, 2017), the SCLM represents a viable source for the anomalously high CO2 fluxes recorded at Etna

A CARBON-RICH SCLM BENEATH ETNA

Findings

CONCLUSIONS