This project proposes to conduct a multi-scale seismic investigation of the tectono/magmatic setting of the Rainbow hydrothermal field, located within a non- transform discontinuity of the Mid-Atlantic Ridge (36°14’N). The main goals are (1) to determine the nature, geometry, and location of the heat source driving high- temperature circulation at Rainbow; (2) to determine the structure and origin of the ultramafic massif that hosts the hydrothermal field; and (3) to image large (detachment) and small-scale faults and investigate how they link to the heat source and control hydrothermal fluid focusing and discharge.