Integrating Olivine Diffusion Chronometry With Monitoring Data to Decipher the Magma Dynamics at the Submarine Fani Maoré Volcano

Monitoring data are critical for understanding volcanic unrest and eruption, but they often lack the ability to constrain the pre‐eruptive magma processes. As such, an increasing number of studies couple monitoring data with petrological tools to obtain insights into the causes and durations of magmatic processes. The 2018–2020 eruption of the submarine Fani Maoré (FM) volcano, Comoros Archipelago, is an excellent location to correlate diffusion chronometry with real‐time monitoring data. Zoned olivine in FM testify that deep basanitic magma interacted with a more evolved reservoir. Diffusion modeling in olivine shows an increase in the magma interaction times (0.5–3 to ∼20 months) as the eruption progresses, implying that basanitic magma stalled near the more evolved reservoir. Additionally, two major intrusive events were identified—in March 2019 and March 2020. The first intrusion occurred as seismic and deformation signals decreased possibly due to enhanced mixing and unlocking of the more evolved mushy reservoir after intrusion. The second intrusion correlates with a change in the locations of seismic events before seismicity and deformation become minor, implying that this intrusion occurred before magma drainage and waning of the eruption. Lastly, by coupling diffusion geochronometry and geophysical monitoring, the magmatic reservoir at FM can be placed at a greater depth (∼30 km) than previously thought, which is consistent with seismic events. Hence, our integrated approach of petrologic tools and real‐time monitoring aids in providing new insights into the magma storage locations and magma‐mush interactions at submarine volcanos.