Corrugated slip surfaces formed at ridge–transform intersections on the Mid-Atlantic Ridge

Abstract

The strips of ocean crust formed at the inside corners of both transform and non-transform offsets on the Mid-Atlantic Ridge are punctuated by topographic highs—the 'inside-corner highs'^1–3—where plutonic rocks (including gabbros and peridotites) are frequently found^4,5. Current tectonic models consider the inside-corner highs to be lower-crust and upper-mantle materials that have been exhumed by low-angle detachment faults dipping away from the inside corner to beneath the ridge axis^3,6–8. But much of the evidence for the existence of such faults has hitherto been circumstantial. Here we present sonar images of two ridge–transform intersections on the Mid-Atlantic Ridge (near 30° N), which show that both active and 'fossil' inside-corner highs are capped by planar, dipping surfaces marked by corrugations and striations oriented parallel to the plate spreading direction. Although these surfaces may be the low-angle detachment faults envisaged by the models, they dip at much shallower angles than expected. This could be explained by the lubricating presence of serpentinized peridotite, fragments of which have been dredged from both surfaces. Alternatively, these slip surfaces may instead represent failure surfaces in serpentine-lubricated landslide zones.