Subduction of Oceanic FracTure zones : the role of slab hydration on the short- to long-term dynamics of subduction zones – SOFT

Recent observations suggest that oceanic fracture zones (OFZ) have a major influence on the dynamic of subduction zones with production of more earthquakes and lavas with distinct composition in regions where OFZ are subducting. The goal of SOFT is to understand how and why OFZ control the short-term (seismic) and long-term (tectonic) dynamic of subduction zones. The hypothesis that will be tested is that the distinct geochemical cycle and seismogenic behaviour where OFZ are subducting result from higher hydration and/or alteration of the oceanic lithosphere due to intense and deep hydrothermal circulation on Oceanic Transform Faults (OTF), the seismically active portions of OFZ.
To tackle those questions and unknowns, SOFT comprises 3 complementary parts. The composition and rheology of the lithosphere on OTF and OFZ will first be constrained from an integrated (petrological-geochemical-(micro)structural) characterization of crustal and mantle samples exhumed from different depths of Atlantic and Pacific TF zones (0 to ~30km depth). The impact of subduction of this hydrated lithosphere on the long-term dynamics and geochemical cycle of subduction zones will be evaluated through 2D and 3D geodynamic models that include the effect of metamorphic reactions and fluids. Last, the influence of OFZ on the seismic dynamics of subduction will be estimated from the (1) analysis of worldwide historic large earthquakes to determine their impact on coseismic rupture nucleation and propagation and (2) characterization of along-strike variations in seismicity across the Lesser Antilles arc where OFZ are being subducted to assess their role on the extent, distribution, spatiotemporal evolution and characteristics of produced seismicity.
Through integration of these different parts, SOFT will be a unique interdisciplinary opportunity to constrain the respective impact of slab hydration and dehydration reactions on the seismic and tectonic dynamic of subduction zones.