Mid-Ocean Ridges and Their Geomorphological Features

Abstract

Most of the Earth's surface is paved by oceanic crust formed along mid-ocean ridges, a ~65,000km long volcanic chain, and one of the most prominent morphologic features on the planet. Seafloor morphology is thus shaped, at large spatial scales (tens to hundreds of km) by the overall ridge geometry, and in particular by both transform faults and non-transform discontinuities that dissect the ridge axis, defining ridge segments, and leave off-axis wakes in seafloor morphology. At smaller scales (tens of km and less) morphological variability is primarily controlled by the relative importance of tectonic and volcanic processes on-axis, in addition to hydrothermal activity on very local scales. While spreading rate is classically invoked as a primary control on ridge segmentation and seafloor morphology, the strongest controls are in fact melt supply to the ridge axis and on-axis lithospheric thickness. Fast-spreading ridges (>60mm/year) show relatively consistent and homogeneous morphologies, dominated by volcanism with limited tectonic reshaping by normal faults. With decreasing spreading rate, the variability in seafloor morphology increases, and encompasses seafloor similar to that formed at fast-spreading ridges wherever magma supply is important, and amagmatic spreading dominated by faulting, while also displaying significant variations at the scale of individual ridge segments. In all cases, tectonic deformation is pervasive, and fault-bounded abyssal hills formed on-axis are ubiquitous throughout the seafloor. Seafloor relief is also modified by mass wasting, which is particularly active along tectonic scarps (e.g., normal faults, walls of rift and transform valleys), and by sedimentation of pelagic or continental origin. This article provides an overview of seascapes formed at mid-ocean ridges and interprets them as the interaction of relief-creating and relief-reworking processes on a range of scales.