Retrograde phases of former bridgmanite inclusions in superdeep diamonds

Dmitry Zedgenizov, Hirioyuki Kagi, Eiji Ohtani, Tatsuki Tsujimori, Kazuki Komatsu

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

(Mg,Fe)SiO3 bridgmanite is the dominant phase in the lower mantle; however no naturally occurring samples had ever been found in terrestrial samples as it undergoes retrograde transformation to a pyroxene-type structure. To identify retrograde phases of former bridgmanite single-phase and composite inclusions of (Mg,Fe)SiO3 in a series of superdeep diamonds have been examined with electron microscopy, electron microprobe, Raman spectroscopy and X-ray diffraction techniques. Our study revealed that (Mg,Fe)SiO3 inclusions are represented by orthopyroxene. Orthopyroxenes in single-phase and composite inclusions inherit initial chemical composition of bridgmanites, including a high Al and low Ni contents. In composite inclusions they coexist with jeffbenite (ex-TAPP) and olivine. The bulk compositions of these composite inclusions are rich in Al, Ti, and Fe, which are similar but not fully resembling Al-rich bridgmanite produced in experiments on the MORB composition. The retrograde origin of composite inclusions due to decomposition of Al-rich bridgmanite may be doubtful because each of observed minerals may represent coexisting HP phases, i.e. bridgmanite or ringwoodite.

Original languageEnglish
Article number105659
Number of pages7
JournalLithos
Volume370-371
DOIs
Publication statusPublished - 1 Oct 2020

Keywords

  • Bridgmanite
  • Jeffbenite
  • Lower mantle
  • Superdeep diamonds
  • MATO-GROSSO
  • JUINA AREA
  • ALMANDINE-PYROPE PHASE
  • DEEP MANTLE
  • HETEROGENEITY
  • LOWER-MANTLE
  • MINERAL INCLUSIONS
  • SUBDUCTED BASALTIC CRUST
  • PEROVSKITE
  • TRANSITIONS

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