The magnetic signature of oceanic core complexes

The magnetic signature of Oceanic Core Complexes (OCCs) remains elusive. Only a few magnetic surveys exist, and their interpretation is complex due to the multiple rock types, insufficient coverage and resolution, and magmatic processes subsequently modified by tectonic deformation. For some of the best studied OCCs along the Mid-Atlantic Ridge at 13°N, this is further complicated by the fact that N-S trending magnetized features near the magnetic Equator generate low amplitude anomalies. We present two magnetic data sets to unravel the deep structure of the OCCs and their magmatic variability. The first case, from the high-resolution bathymetric and magnetic surveys of the MAR 13°N OCCs, reveals magnetized bodies within the OCC domal structure, interpreted here as gabbro bodies and truncated dykes. The second case is from sea-surface magnetic anomalies collected over large OCCs of the Carlsberg Ridge that unambiguously record geomagnetic reversals, pointing instead to a continuous gabbro layer and truncated dykes as the most likely source of magnetization. Our results underline the major role of gabbro bodies and truncated dykes, cooled in the neovolcanic zone and carried off-axis as the footwall progressively exhumes, in shaping the magnetic anomalies observed above OCCs, and the variability in the emplacement of these bodies among different detachment systems.