Crustal Accretion, Significant Mantle Uplift, and Exhumation along Non-transform Discontinuities: Equatorial Mid-Atlantic Ridge (7º 10’ – 0º 50’ N)

Abstract

The exhumation and exposure of mantle rocks is a common process that takes place during the tectono-magmatic evolution of a newly created lithosphere along slow- and ultraslow-spreading oceanic ridges, such as the Equatorial Mid-Atlantic Ridge. A geophysical survey conducted in 2012 and 2013 between the Bogdanov (7º 10’ N) to the St. Paul (0º 50’ N) fracture zones revealed lower crust and upper mantle rocks exposures through asymmetric accretion along low-angle normal faults, i.e., the Oceanic Core Complexes, laterally associated with other morpho-tectonic features. The dataset consists of multi-beam bathymetry (100 m/pixel) and ship gravity (1,750 m/pixel) covering an area of 40,000 km². Seismicity and satellite free-air anomaly data are included. Three oceanic transform faults and nine non-transform offsets were identified and mapped along the ridge axis. Oceanic Core Complexes are characterized by corrugated and non-corrugated massifs, back-tilted ridges indicating detachment breakaways, and various detachment morphologies. These features typically exhibit bathymetric patterns that are roughly parallel to the accretion direction, positive Bouguer anomalies, and low seismic activity. Twelve Oceanic Core Complexes consistently occur at non-transforming discontinuities and asymmetric accretion segments. These mantle outcroppings indicate a low melt supply during the recent tectono-magmatic evolution of this region of the Mid-Atlantic Ridge.