A model of buoyant ridge subduction: effects of ridge width, buoyancy and obliquity

The subduction of buoyant ridges has commonly been invoked as a mechanism to produce flat subduction, cessation of arc magmatism, increased seismicity and orogenic shortening. Whilst the spatial correlation of ridges with flat slabs and amagmatic arcs in the East Pacific is strong, the correlation in the West Pacific is significantly weaker. To constrain the relative ridge buoyancy and widths required to obtain flat subduction, we perform 3D coupled finite and boundary element simulations of the subduction of plates containing ridges of various widths and densities. We show that plateau geometry and buoyancy exert independent controls on slab morphology and magmatic arc migration. A further influence comes from obliquity of the ridge to the trench, which can also lead to trench rotation. As an example, 400km-wide ridges of 45o and 63o obliquity replicate pseudo-flat subduction, and an anti-correlation between the ridge at the trench and shallow dip. We conclude that the strong versus weak correlation between ridge subduction and flat slabs occurring in the West and East Pacific respectively, may be due, in part, to differences in the relative buoyancy of eastern and western Pacific ridges compared to the underlying slab and in part to differences in buoyant ridge obliquity.