Formation conditions of the young flat-slab in the wedge subduction zone

Abstract

A wedge subduction can initiate after a ridge subduction and is characterized by the young and thin part of the plate subducting first. A series of 2D geodynamical models were built to investigate the factors in the development of a young flat-slab during the wedge subduction process after a ridge subduction. The factors include the convergence rate, the half spreading rate of the ridge, the initial subduction angle, and the thickness of the overriding plate. The results show that a flat-slab generally forms before the slab age reaches 40 Myr, except in special cases, for instance, when convergence rate≤1 cm/yr, the half spreading rate is low, or the initial subduction angle≥55°. The wedge subduction slab is prone to flatten because the young wedge subduction slab is naturally accompanied by buoyancy anomaly and has the potential to flatten at the relatively low convergence rate. There is no evidence as to whether a flat-slab exists south of Chile Triple Junction. According to the simulation results, the tomographic evidence, and the oceanic age distribution, it can be inferred that, from 46.5°S to ∼50°S, the wedge subduction is in the initiation stage and the formation of a flat-slap is impossible. Near 50–52°S, the slab possibly flattens when the initial subduction angle is 20–30°. From ∼52°S to ∼55°S, when the initial subduction angle is 20–40°, a flat subduction is likely to occur.