Tectono-Magmatic Evolution of the Southern Reykjanes Ridge, North Atlantic, From ∼11 M.y. to Present

Our understanding of the geological evolution of mid-ocean ridges in response to tectonic reconfigurations and associated mantle processes is hampered by a lack of exploration in off-axis areas. A notable exception is the Reykjanes Ridge, where multibeam bathymetry, magnetics, and gravity surveys have been conducted up to ∼150 km from the ridge axis. Previous work shows that the ridge has undergone a major reorganization following changes in spreading direction, resulting in the progressive formation and then elimination of transform faults from north to south under the influence of the regional mantle melting anomaly. Notably, this process is incomplete near the southern termination of the ridge, providing a window into the processes of crustal accretion and segmentation prior to and immediately following this reorganization. Here, we employ remote-predictive geological and structural mapping methods linked to chrono-magnetic data to elucidate changes in segment morphology, magma supply, and structural fabrics along the southern ∼200 km of the ridge over the past ∼11 M.y. We identify two new fracture zones and three new non-transform discontinuities, with elimination of transform motion occurring between ∼9.7 and 4.2 Ma, which is later than previously thought. Transform elimination coincides with rift propagation and the emergence of a new magmatically robust segment at ∼58°N at ∼9.7–8.2 Ma. This transition is also associated with a reorientation of seafloor fabric from dominantly N-trending to NE-trending, associated with the dissection of axial volcanic ridges by the oblique (NE-trending) plate boundary, resulting in more crustal accretion to the North American plate overall.