Magnetotelluric evidence for a melt-rich magmatic reservoir beneath Mayotte
Article Date: 2025-10-30
Article URL: https://www.nature.com/articles/s41586-025-09625-4
Article Image: not provided
Summary
This Nature paper reports 3D magnetotelluric (MT) imaging across the Mayotte seismo-volcanic region and identifies a strongly conductive body beneath the island. The conductivity and geometry are interpreted as a melt-rich magmatic reservoir — a relatively large, partially molten region in the crust or uppermost mantle. Authors combine land and marine MT soundings, robust processing and 3D inversion, then compare model conductivities with laboratory-based conductivity laws and petrological constraints to estimate melt fraction, volatile content and the reservoir’s likely role in the 2018–ongoing Mayotte submarine eruption and associated crustal deformation.
Key Points
- 3D magnetotelluric imaging reveals a pronounced conductive anomaly beneath Mayotte consistent with a melt-rich reservoir.
- The conductive body is spatially correlated with regions of intense seismicity and previously observed deformation from the 2018–2019 crisis.
- Comparison with experimental conductivity models suggests appreciable melt fractions and/or hydrous melts rather than solely saline fluids or clay-rich rocks.
- The reservoir geometry supports a transcrustal magmatic system interpretation and helps reconcile seismic, petrological and geodetic observations from the Mayotte event.
- Results imply a significant mobile magmatic component (melt-rich mush) that could feed submarine eruptions and drive long-term deformation.
- The study demonstrates the power of combined land/marine MT plus laboratory constraints to map melt beneath ocean islands.
Content summary
The authors deployed a combined land and marine magnetotelluric dataset across Mayotte, processed the data with robust tools and performed full 3D inversions. The resulting resistivity models show a low-resistivity body at depths consistent with a mid-to-lower crustal to lithosphere-asthenosphere location. By testing conductivity scenarios (variations in melt fraction, melt composition, water/CO2 content and temperature) against laboratory-derived conductivity laws, they favour an interpretation involving a melt-rich reservoir or high-porosity mush rather than only hydrous minerals or brines.
The paper places the MT results alongside seismic tomography, local earthquake distributions and surface deformation to build a coherent picture: a large-scale magmatic system underpins the 2018 seismo-volcanic crisis and subsequent submarine eruptive activity. The authors discuss implications for magma storage architecture (mush vs melt-dominated zones), volatile supply and potential eruptive behaviour, and they highlight how MT can detect melt that is otherwise seismically ambiguous.
Context and relevance
Mayotte attracted global attention after intense seismic swarms and an exceptional submarine eruption beginning in 2018. Determining whether deep magma drained or whether melt remains stored is crucial both for scientific understanding and hazard assessment. This MT study adds a direct geophysical constraint on melt presence and distribution, complementing seismic, petrological and geodetic studies. It also advances methodology for mapping melt beneath ocean islands and rift-related volcanism — a growing focus given increasing offshore monitoring and interest in submarine eruptions.
For researchers, the work refines models of transcrustal magma plumbing and melt retention. For local authorities and hazard modellers, evidence of a sizeable melt-rich reservoir changes how future unrest scenarios might be framed (rate and style of eruption, potential for renewed submarine activity, and longer-term crustal adjustment).
Why should I read this?
Short version — this paper actually shows where the goo is. If you care about the Mayotte crisis, volcanic hazards, or how geophysicists detect melt under islands, it saves you time by pulling MT, lab data and seismic/geodetic results together into one convincing picture. Also handy if you want a clear example of how magnetotellurics can reveal melt that seismic methods alone might miss.
Author style
Punchy: the authors don’t just run an inversion and stop — they test competing conductivity explanations and explicitly link the MT image to the eruption and seismicity. If you follow volcano monitoring or subsurface melt dynamics, this paper is highly relevant and worth reading in detail.