Plate motion and plume-induced subduction initiation

Abstract

Impingement of a hot buoyant mantle plume head on the lithosphere is one of the few scenarios that can initiate a new subduction zone without requiring any pre-existing weak zones. This mechanism can start subduction and plate tectonics on a stagnant lid and can also operate during active plate tectonics where plume-lithosphere interactions is likely to be affected by plate motion. In this study, we explore the influence of plate motion on lithospheric response to plume head-lithosphere interaction including the effect of magmatic weakening of lithosphere. Using 3d thermo-mechanical models we show that the arrival of a new plume beneath the lithosphere can either (1) break the lithosphere and initiate subduction, (2) penetrate the lithosphere without subduction initiation, or (3) spread asymmetrically below the lithosphere. Outcomes indicate that lithospheric strength and plume buoyancy control plume penetration through the lithosphere whereas the plate speed has a subordinate influence on this process. However, plate motion may affect the geometry and dynamics of plume-lithosphere interaction by promoting asymmetry in the subduction zone shape. When a sufficiently buoyant plume hits a young but subductable moving lithosphere, a single-slab modern-style subduction zone can form instead of multiple subduction zones predicted by stagnant lid models. In the case of subduction initiation of older moving oceanic lithosphere, asymmetrical cylindrical subduction is promoted instead of more symmetrical stagnant lid subduction. We propose that the eastward motion of the Farallon plate in Late Cretaceous time could have played a key role in forming one-sided subduction along the southern and western margin of the Caribbean and NW South America.