Geomorphology of Oceanic Spreading Centers

The morphology of mid-ocean and back-arc spreading centers is largely modulated by the local rate of plate divergence through its impacts on the supply of magma and the strength of the lithosphere. At fast-spreading rates (∼>90 mm/year) oceanic spreading centers are characterized by an axial high, with a summit trough, and flanked by a faulted horst-and-graben terrain. At slow spreading rates (∼<40 mm/year) the axis is marked by a rift valley, with an axial volcanic ridge along its floor, and flanked by predominantly inward-facing normal faults. Along the axis, oceanic spreading centers display a hierarchical pattern of segmentation. The lowest order of segmentation is defined by oceanic transform faults, with higher orders of segmentation marked by non-transform discontinuities that include overlapping spreading centers, oblique rift zones, deviations from linearity and volcanic gaps.