The extensive fast seismic anomalies in the mantle transition zone beneath East Asia are often interpreted as stagnant Pacific slabs, and a reason for the widespread tectonics since the Mesozoic. Previous hypotheses for their formation mostly emphasize vertical resistances to slab penetration or trench retreat. In this study, we investigate the origin of these stagnant slabs using global-scale thermal-chemical models with data-assimilation. We find that subduction of the Izanagi-Pacific mid-ocean ridge marked the transition of mantle flow beneath western Pacific from being surface-driven Couette-type flow to pressure-driven Poiseuille-type flow, a result previously unrealized. This Cenozoic westward mantle wind driven by the pressure gradient independently explains seismic anisotropy in the region. We conclude that the mantle wind is the dominant mechanism for the formation of stagnant slabs by advecting them westward while the pressure gradient holds them in the transition zone.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)