Generation of morphotectonic fabric on the Mid‐Atlantic Ridge flanks, 28° to 29°N: Implications for the limits of tectonic deformation and abyssal hill formation

Abstract

High‐resolution multibeam bathymetry is used to analyze the morphotectonic fabric of a 35,000‐km2 zone of the Mid‐Atlantic Ridge crest between 28° and 29°N. Interpolated isochrons at 1 Myr intervals derived from a kinematic reconstruction provide a temporal framework for the structural analysis. The axial valley within the survey area is offset by three non‐transform discontinuities dividing the axis into en echelon segments. The flanks display a predominantly ridge‐parallel fabric of elongate abyssal hills crosscut by several discordant zones. Throughout the zone faulting is the predominant factor in generating the morphotectonic fabric. Analysis of fault scarp distribution places the limit of active tectonic deformation between 2 and 3 Ma (25 to 35 km on either side of the spreading axis). Fault scarp relief on the ridge flanks varies with a period of approximately 2 Myr which corresponds to the wavelength of abyssal hills within the area. We propose an interpretation in which abyssal hill formation occurs periodically (∼2 Myr) within the ridge mountains as the lithosphere transitions from the dynamic supported regime near the axis to the isostatic regime of the flanks at ∼2–3 Ma (∼25–35 km from the axis).