In a document published in the journal Geology, the scientists explain that over geological time, variations in atmospheric CO2 depended mainly on volcanic emissions, which are difficult to estimate because they are not directly related to the volume of magmas that erupted. Indeed, some volcanoes have exceptionally large emissions of CO2 compared to the amount that can be dissolved in their magmas. Mount Etna is perhaps the most striking example, contributing 10% (9,000 tonnes/day) of current global volcanic CO2 emissions. That’s three times more CO2 than a volcano like Kilauea in Hawaii emits, which erupts four times as much magma.
But the Nb/Ta ratios are very constant in many rocks and are only modified by a few geological processes, such as the infiltration of carbonate-rich magmas into the Earth’s mantle.
In this regard, the study revealed that the Etna and Mount Vulture magmas are characterized by extremely high Nb/Ta ratios, higher than any other active intraplate volcano. This means that the magmatic compositions testify to the presence of extremely carbon-rich lithospheric mantle domains beneath southern Italy. This carbon is “captured” during the melting of magmas.
The process is directly related to the complex geodynamic setting of the region: carbon-rich lithospheric mantle domains are located beneath the Hyblaean Plateau in southern Sicily. These domains are transported to the region under Etna by means of tectonic activity, in particular the retreat of the Ionian subduction plate. A symmetrical mechanism probably occurs on the other side of the Ionian plate, below Mount Vulture.
“The data also allow us to infer the contribution of these carbon-rich domains to the Earth’s atmosphere in the past, suggesting that Etna’s CO2 emissions during its ancient activity could have been even higher than ‘at present,’ Carsten Münker, co-author of the study, said in a press release. He and his team were responsible for high precision measurements including the two critical elements Nb and Ta.
In the opinion of Münker and colleagues, the innovative trace element approach used in this study represents a promising avenue to better estimate the contribution of carbon-enriched lithosphere to global volcanic CO2 emissions, both current and past. , which may have played a key role in climate change on our planet.
“Similar carbon-rich domains could be hidden beneath other volcanoes around the world, contributing to their CO2 emissions,” lead author Alessandro Bragagni noted in the memoir.