11:45 AM - 12:00 PM
[SIT20-11] Core-mantle interaction evidence from SiO2 dispersal in Earth's lower mantle
Keywords:SiO2, core, mantle
As the Earth accreted and progressively grew its core, Si and O probably dissolved into the metal and were kept there for some time. As the core subsequently cooled, SiO2 would have been expelled due to oversaturation, a process that could continue today. On account of SiO2's low density with respect to the lowermost mantle, we examine the process of SiO2 accumulation at the core-mantle boundary (CMB) and its incorporation into the mantle by buoyant rise. Diapirs formed by the viscous Rayleigh-Taylor instability in the SiO2 collected at the CMB would cause them to be swept into the mantle as inclusions of 100 m - 10 km diameter today, using estimates of SiO2 viscosity in the lower mantle. Under early Earth conditions of rapid heat loss after core formation, smaller, ~1 km diameter diapirs could have risen independently of mantle flow to a level of neutral buoyancy in the lower mantle, trapping them there. SiO2 presence could account for small-scale scattering in the lower mantle due to the bodies' large velocity contrast with peridotite.