The thermal equation of state of (Mg, Fe)SiO3 bridgmanite (perovskite) and implications for lower mantle structures. Issue 11 (21st November 2015)

• Record Type: Journal Article
• Authors: Wolf, Aaron S.; Jackson, Jennifer M.; Dera, Przemeslaw; Prakapenka, Vitali B.
• Is Part Of: Journal of geophysical research. Volume 120:Issue 11(2015:Nov.)
• Page Start: 7460
• Page End: 7489
• Publication Date: 2015-11-21
• Subjects: bridgmanite -- perovskite -- equation of state -- LLSVP -- mantle geotherm; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2015JB012108
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: The high‐pressure/high‐temperature equation of state (EOS) of synthetic 13% Fe‐bearing bridgmanite (Mg silicate perovskite) is measured using powder X‐ray diffraction in a laser‐heated diamond anvil cell with a quasi‐hydrostatic neon pressure medium. We compare these results, which are consistent with previous 300 K sound speed and compression studies, with a reanalysis of Fe‐free Mg end‐member data from Tange et al. (2012) to determine the effect of iron on bridgmanite's thermoelastic properties. EOS parameters are incorporated into an ideal lattice mixing model to probe the behavior of bridgmanite at deep mantle conditions. With this model, a nearly pure bridgmanite mantle composition is shown to be inconsistent with density and compressibility profiles of the lower mantle. We also explore the buoyant stability of bridgmanite over a range of temperatures and compositions expected for Large Low‐Shear Velocity Provinces, concluding that bridgmanite‐dominated thermochemical piles are more likely to be passive dense layers externally supported by convection, rather than internally supported metastable domes. The metastable dome scenario is estimated to have a relative likelihood of only 4–7%, given the narrow range of compositions and temperatures consistent with seismic constraints. If buoyantly supported, such structures could not have remained stable with greater thermal contrast early in Earth's history, ruling out formation scenarios involving a large concentration of heat producing elements. Key Points: High P‐T equation of state of 13% and 0% Fe bridgmanite (perovksite) is obtained Pure bridgmanite mantle is inconsistent with PREM at any Fe content Buoyant stability of LLSVPs favors passive chemical piles over metastable domes