Abstract

3D full waveform inversion (FWI) has been applied to the seismic refraction data of the MARINER (Mid-Atlantic Ridge INtegrated Experiment at Rainbow) experiment to create a robust high-resolution model of the seismic velocity structure of the Rainbow massif. The Rainbow massif is an oceanic core complex located on a non-transform discontinuity (NTD) in a magma-starved region of the mid-Atlantic Ridge at 36ºN. Despite the low magmatic input, the core complex hosts a high-temperature hydrothermal vent field  (>340°C) that requires a long-lived magmatic heat source. The FWI results show that deep within the massif, ∼3-8 km below the seafloor, lies a low-velocity body that represents a partially molten sill complex. The sill complex extends north to the AMAR Minor N segment suggesting an increased magmatic input into this segment, forcing the NTD to migrate southwards. Extensive magmatic intrusion into the core complex was likely responsible for termination of slip on the detachment fault. We model hydrothermal fluid flow inside the Rainbow massif using the Imperial College Finite Element Reservoir Simulator (IC-FERST). The model geometry, thermal properties, flow properties and boundary conditions are informed by the seismic constraints. We show that the high temperatures within the core of the Rainbow massif prevent serpentinization from taking place and govern the location of the serpentinization front.