Dynamics of Plate Tectonics and Mantle Convection - Chapter 20: Mid-Ocean Ridges: Geodynamics Written in the Seafloor

Mid-ocean ridges are divergent plate boundaries where new oceanic crust and lithosphere form through a complex interplay of magmatic, hydrothermal, and tectonic processes. Magma is generated tens of km below the ridge by adiabatic decompression of upwelling asthenosphere. It ascends and collects at the ridge axis, where it is emplaced as oceanic crust, bringing heat that fuels hydrothermal convection. Repeated intrusions of melt into the lithosphere accommodate a sizeable fraction of plate divergence, thereby modulating the properties of faults that take up the remaining fraction. This chapter uses simple analytical models to draw connections between the thermal state of the sub-ridge asthenosphere, its magmatic productivity, and the thermomechanical properties of young oceanic lithosphere, which deforms in the presence of magma to shape the Earth's seafloor. This provides first-order guidelines to interpret the ∼200Myr-long seafloor record in terms of the transient dynamics of the upper mantle.