Causes of oceanic crustal thickness oscillations along a 74‐Myr Mid‐Atlantic Ridge flow line

International audience1. We conducted one of the longest continuous geophysical surveys along a 74-Myr 15 spreading-parallel flow line across the Mid-Atlantic Ridge. 16 2. Spectral densities of bathymetry and gravity data show concurrent peaks at 390-, 550-, 17 and 950-kyr periods, and diffuse power at >1 Myr. 18 3. A negative correlation between fault spacing and gravity-derived crustal thickness 19 suggests a link between magma input and fault style. 20 21 Abstract: 22 Gravity, magnetic, and bathymetry data collected along a continuous 1400-km-23 long spreading-parallel flow line across the Mid-Atlantic Ridge indicate significant 24 tectonic and magmatic fluctuations in the formation of oceanic crust over a range of 25 timescales. The transect spans from 28 Ma on the African Plate to 74 Ma on the North 26 American plate, crossing the Mid-Atlantic Ridge at 35.8 ºN. Gravity-derived crustal 27 thicknesses vary from 3-9 km with a standard deviation of 1 km. Spectral analysis of 28 bathymetry and residual mantle Bouguer anomaly (RMBA) show diffuse power at >1 29 Myr and concurrent peaks at 390, 550, and 950 kyr. Large-scale (>10-km) mantle thermal 30 and compositional heterogeneities, variations in upper mantle flow, and detachment 31 faulting likely generate the >1 Myr diffuse power. The 550-and 950-kyr peaks may 32 reflect the presence of magma solitons and/or regularly spaced ~7.7 and 13.3 km short-33 wavelength mantle compositional heterogeneities. The 390-kyr spectral peak corresponds 34 to the characteristic spacing of faults along the flow line. Fault spacing also varies over 35 longer periods (>10 Myr), which we interpret as reflecting long-lived changes in the 3