New research has revealed the intriguing connection between deep mantle earthquakes and the release of carbon dioxide (CO2) at the Mid-Atlantic Ridge (MAR), shedding light on the complex processes involved in magma migration beneath oceanic spreading centers. Conducted by Yu et al. and published on January 1, 2025, the study provides compelling evidence linking deep seismic activities—occurring at depths of 10 to 20 kilometers below the surface—directly to CO2 degassing from magma.
The significance of this study lies not only in the discovery of these deep earthquakes but also in their potential to transform our current understandings of the melting mechanisms and volatiles' roles during the formation of oceanic crust. Traditionally, it has been believed seismic events at these depths were less common, with expectations placing the maximum earthquake depth considerably lower. "We suggest the small pressure increase due to CO2 degassing from the ascending melt induces the earthquakes observed beneath the RC2 ridge axis," said the authors. Their findings suggest high concentrations of CO2—which ranged between 0.4 to 3.0 weight percent (wt%)—in the primary melts may significantly influence these events.
The study's methodology incorporated seismological data gathered from ocean-bottom seismometers deployed along the MAR, complemented by geochemical analyses of basalt samples acquired during the SMARTIES cruise held in 2019. This comprehensive approach enabled researchers to directly link the observed seismicity to the geochemical characteristics of the melts beneath the ridge. Previous studies had primarily focused on shallow seismic events, leaving the deep-seated processes nearly uncharted until now.
The deep earthquakes identified by the researchers are not merely anomalies; they provide insight to the geological processes occurring beneath the surface. These phenomena have potential ramifications for our knowledge of mantle dynamics and the overall volatility of melts beneath mid-ocean ridges. Further exploration may reveal more about how CO2 can act as both fluid and volatile, changing the mechanical properties of surrounding rocks and inducing seismicity at such remarkable depths.
The research team posits two key hypotheses for the observed seismic activity. The first is the dynamic interplay between CO2 degassing and pressure fluctuations within the ascending magmas, which can trigger earthquakes. According to the authors of the article, "These results indicate the penetrative influence of CO2 on deep earthquake activity at slow-spreading ridges." The second hypothesis raises the possibility of hitherto unexplored magma migration pathways or potential tectonic features facilitating these deep seismic events.
This study's results have opened avenues for future geological explorations and sparked scientific discourse around the dynamic and often volatile nature of the Earth's mantle, particularly beneath oceanic environments. Researchers also contend these insights can influence models predicting the geological behavior of unexplored regions within the MAR and other slow-spreading ridges worldwide.
With the MAR being characterized as one of the slowest spreading mid-ocean ridges, this research highlights the need for more focused investigations of hydrothermal systems and their interactions with the geological environment. Understanding the CO2 content and its impact on melt migration could help clarify the broader geological narrative, addressing questions ranging from earthquake genesis to the formation of new oceanic crust.
Researchers plan to extend their study, potentially influencing approaches to monitoring seismic activity and mitigating natural hazards associated with deep-seated earthquakes. Overall, this study marks significant progress, not only enhancing our comprehension of mid-ocean ridge dynamics but pointing to the unrevealed mysteries the deep Earth still holds.