Ridge jumps and propagations in the South Atlantic Ocean

Abstract

THE normal pattern of mid-ocean-ridge divergent plate boundaries comprises straight spreading segments with narrow zones of crustal accretion, bounded by transform faults where these segments are offset. Normally the configuration of spreading segments and transform faults is stable for long periods, but in places on fast and medium-rate spreading ridges the transform offsets have propagated along the ridge axis as some spreading segments have grown at the expense of adjacent ones^1–7. Although such behaviour has hitherto not been well documented on slow-spreading ridges, we have mapped multiple ridge jumps and propagating rifts in two areas of the slow-spreading (18 mm yr⁻¹ half rate) South Atlantic ridge crest. We attribute this anomalous behaviour in the South Atlantic to the presence of hotspots near our study areas, causing elevated asthenospheric mantle temperatures and lateral mantle flow, with consequent excess volcanism and disruption of the normally well focused melt delivery processes at the ridge crest.