Phase transition zone width implications for convection structure

Abstract

In the Ringwood pyrolitic (pyroxene‐olivine) model, the upper mantle consists of peridotite (90%) and eclogite (10%). Peridotite includes olivine (60%), orthopyroxene (25%), clinopyroxene, and garnet. Eclogite contains clinopyroxene (60%), garnet (30%), and other minor admixtures. The lower mantle consists of silicate perovskite (Mg 0.9 Fe 0.1 )SiO 3 (75%), magnesiowustite (Mg 0.8 Fe 0.2 )O (15%), and calcium perovskite (CaSi)O 3 (10%) [Davies, 1999]. With an increase in pressure and temperature, the mantle material experiences phase transitions. Since it has a multicomponent composition, the transition does not occur in a jumpwise manner but is distributed over an interval of pressures ∆ p or depths d = ∆ p /( ρ g ) . At a depth of 410 km, olivine is transformed into wadsleyite with a density jump of δρ / ρ 0 = 0.07 at a phase equilibrium curve slope of γ = dp / dT = 1.6‐3.0 MPa/K; the width of the phase transition zone is d = 13 km. At a depth of 520‐580 km, wadsleyite is transformed into