It is estimated that ~75% of Earth’s volcanism occurs on the seafloor, especially at divergent plate boundaries like the East Pacific Rise and the mid-Atlantic Ridge (Crisp, 1984). These features are known as mid-ocean ridges (MORs), which are large-scale lineaments marking areas of seafloor spreading where lavas are extruded onto the seafloor, and subseafloor dike emplacement is common. A metaphor commonly ascribed to this process is “conveyor belt,” where newly formed oceanic crust, invariably of basaltic composition, moves inexorably away from the axis of the MORs as the forces of plate tectonics take hold. Conversely, at the other...

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