title: Multiple seismic reflectors in Earth's lowermost mantle.
abstract: The modern view of Earth's lowermost mantle considers a D″ region of enhanced (seismologically inferred) heterogeneity bounded by the core-mantle boundary and an interface some 150-300 km above it, with the latter often attributed to the postperovskite phase transition (in MgSiO3). Seismic exploration of Earth's deep interior suggests, however, that this view needs modification. So-called ScS and SKKS waves, which probe the lowermost mantle from above and below, respectively, reveal multiple reflectors beneath Central America and East Asia, two areas known for subduction of oceanic plates deep into Earth's mantle. This observation is inconsistent with expectations from a thermal response of a single isochemical postperovskite transition, but some of the newly observed structures can be explained with postperovskite transitions in differentiated slab materials. Our results imply that the lowermost mantle is more complex than hitherto thought and that interfaces and compositional heterogeneity occur beyond the D″ region sensu stricto.
authors.affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Shang
authors.forename: Sang-Heon
authors.initials: SH
authors.lastname: Shim
authors.forename: Maarten
authors.initials: M
authors.lastname: de Hoop
authors.forename: Robert
authors.initials: R
authors.lastname: van der Hilst
mesh_terms: D017610:Calcium Compounds / Q000737:chemistry; D018481:Convection; D018534:Earth, Planet; D055593:Geological Phenomena; D017633:Magnesium Silicates / Q000737:chemistry; D008962:Models, Theoretical; D010087:Oxides / Q000737:chemistry; D014025:Titanium / Q000737:chemistry
chemical_list: D017610:Calcium Compounds; D017633:Magnesium Silicates; D010087:Oxides; C059910:perovskite; D014025:Titanium
keywords: mantle convection; mineral physics; seismic imaging