Phase transformations in the earth's mantle and subducting slabs: Implications for their compositions, seismic velocity and density structures and dynamics

摘要: Phase transformations in model mantle compositions and those subducting slabs have been reviewed to a depth of 800 km on the basis recent high-pressure experimental data. Seismic velocity density profiles these also calculated using other mineral physics The nature seismic for pyrolite composition was found generally agree with determined by observations (e.g. PREM). locations discontinuities at 400 670 correspond almost exactly depths where olivine component denser phases take place. Moreover, steep gradients velocity/density observed between are qualitatively consistent expected from successive complementary pyroxene-garnet composition. Further, values well upper transition region within uncertainties attached calculations observations. Pyrolite or peridotite thus most likely represent above depth, although some degrees chemical heterogeneity may exist region. sharp discontinuous increases velocities this be attributed either phase transformation perovskite-bearing assemblage changes. Density subducted along adequate geotherms assuming that composed former oceanic crust underlain thicker harzburgitic layer. It is shown substantially less dense than surrounding below km, while it trapped region, forming geochemically enriched layer mantle-lower boundary. Thick cool penetrate into lower mantle, but chemically derived buoyancy result strong deformation formation megalith structures around discontinuity. These detected tomography studies subduction zones.