We present results from 3D processing of 2D seismic data shot along 100 m-spaced profiles in a 1.8 km wide by 24 km long box during the SISMOSMOOTH 2014 cruise. The study is aimed at understanding the oceanic crust formed at an end-member mid-ocean ridge environment of nearly zero melt supply. Three distinct packages of reflectors are imaged: (1) south-facing reflectors which we propose correspond to the damage zone induced by the active axial detachment fault. Reflectors in the damage zone have dips up to 60° and are visible down to 5 km below the seafloor; (2) series of north-dipping reflectors in the hanging wall of the detachment fault. These reflectors may correspond to damage zone inherited from a previous, north-dipping detachment fault, or small offset recent faults, conjugate from the active detachment fault, that served as conduits for isolated magmatic dykes; (3) discontinuous but coherent flat-lying reflectors at shallow depths (< 1.5 km below the seafloor), and at depths between 4 and 5 km below the seafloor. Comparing these deeper flat lying reflectors with the wide-angle velocity model obtained from ocean bottom seismometers (OBSs) data next to the 3D box shows that they correspond to parts of the model with P-wave velocity of 6.5-8 km/s suggesting that they occur in the transition between lower crust and upper mantle. The 4-5 km layer with crustal P-wave velocities is interpreted as primarily due to serpentinization and fracturation of the exhumed mantle-derived peridotites in the footwall of active and past detachment faults.