In slow spreading environments, oceanic crust is formed by a combination of magmatic and tectonic processes. Using full waveform inversion applied to active-source ocean bottom seismometer data, we reveal the presence of a strong lateral variability in the 40 – 48 Ma old oceanic crust at the slow-spreading Mid-Atlantic Ridge in the equatorial Atlantic Ocean. Over a 120 km-long section between the St Paul fracture zone and the Romanche transform fault, we observe four distinct 20-30 km long crustal segments. The segment affected by the St Paul FZ consists of three layers, 2-km thick layer with velocity <6 km/s, 1.5 km thick middle crust with velocity 6-6.5 km/s, and an underlying layer with velocity ~7 km/s in the lower crust. The segment associated with an abyssal hill morphology contains high velocity ~7 km/s from a shallow depth of 2 – 2.5 km below basement, indicating the presence of primitive gabbro. The segment associated with a low basement morphology seems to have 5.5 – 6.5 km/s velocity starting near the basement extending down to ~4 km depth, indicating chemically distinct crust. The segment close to the Romanche transform fault, a normal oceanic crust with velocity 4.5-5 km/s near the seafloor increasing to 7 km/s at 4 km depth indicates a magmatic origin. The four distinct crustal segments have a good correlation with the overlying seafloor morphology. The observed strong crustal heterogeneities could result from alternate tectonic and magmatic processes along the ridge axis, possibly modulated by chemical variations in the mantle.