An examination of 339 topographic profiles crossing the world mid-ocean ridge system indicates that the axial topographic signature is correlated to both the local spreading rate and the absolute depth of the ridge axis. The spreading rate (which controls the temperature structure at the ridge axis) and the depth of the ridge axis (which is an indicator of crustal thickness) are both expected to influence the rheology of the axial lithosphere, which in turn should control the shape of the axial topographic signature. The topographic signature of the axis is determined by fitting an axial high or an axial valley on a trend that follows the thermally driven subsidence of the ridge flanks. At a given axial depth the transition between an axial valley and a high takes place abruptly, over a relatively small change in spreading rate (approximately 15 mm/yr).
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