Magmato-Tectonic Interactions during Seafloor Spreading – MaTISS

Two thirds of Earth's surface formed along the global mid-ocean ridge (MOR) system, where divergence between 2 tectonic plates is accommodated by magmatic accretion and faulting. The relative contribution of magmatism to seafloor spreading is thought to be the primary control on the texture of the ocean floor, and structure of the underlying lithosphere. The current geodynamic paradigm however does not explain how magmatic and tectonic strain partition at a MOR. The MaTISS project seeks to solve this issue by rethinking seafloor spreading as the cumulative sum of discrete magmatic and tectonic events (e.g., magmatic intrusions and fault slip) that influence one another. Our goal is to document such "quantum" events of seafloor spreading, and model their mechanical interactions.

To this end, MaTISS supports an ambitious 3-yr long experiment of seafloor seismo-geodesy across a segment of the Southeast Indian Ridge at 37ºS and its abutting transform fault (full spreading rate: 6.5 cm/yr). Every year between 2024 and 2027, an OHA-GEODAMS cruise (with ship time already secured from the French Oceanographic Fleet: IR* FOF) will return to 37ºS to maintain a seafloor observatory comprising 15 acoustic beacons for direct-path ranging, 2 drift-controlled pressure gauges, 5 hydrophones, and 7 ocean bottom seismometers. These will respectively measure relative seafloor displacements (horizontal and vertical), monitor the regional and local seismicity, and probe the structure of the sub-seafloor. A key novelty of the MaTISS project is that it will jointly monitor an oceanic transform fault and its adjacent spreading segment, shedding new light into the possible synchronicity of deformation between these two systems.

The data will be analyzed with Bayesian inversions to infer the source of deformation transients (e.g., diking, fault slip, or sill inflation). We will then use mechanical modeling to determine whether these spreading events inhibit or promote each other. Finally, we will assess the extent to which short-term interactions between spreading events shape the long-term partitioning of magmatic and tectonic strain encoded in the morphology of the ridge.

In conclusion, the MaTISS project will define a new state of the art in seismo-geodetic seafloor monitoring. For the first time, techniques commonly used on land will be applied to characterize the deformation associated with seafloor spreading.