Microstructures and structural phase transition in (Mg,Fe)SiO3 majorite

Naotaka Tomioka, Kiyoshi Fujino, Eiji Ito, Tomoo Katsura, Thomas Sharp, Takumi Kato

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

(Mg1-x,Fex)SiO3 majorites with the compositions of X=0.0-0.20 were synthesized at 20 GPa and 1950-2200 °C in a uniaxial split-sphere apparatus, and the recovered samples were examined by analytical transmission electron microscopy. Although the diffraction patterns of synthetic majorites in all the recovered specimens show a tetragonal (I41/a) symmetry, specimens quenched from temperatures above ~1950 °C show frequent pseudomerohedral twins and modulated "tweed" structures, while specimens quenched from temperatures below ~1950 °C show few or no twins. Right-angled pseudomerohedral twins domains occur without dislocations to relax strain at the domain corners. These observations suggest that twin and tweed structures in tetragonal majorite form by the cubic-tetragonal phase transition during quenching and that cubic majorite is stable at temperatures above ~1950 °C at 20 GPa. Natural majorites in shocked chondrites appear to be cubic. The difference between natural cubic majorites in shocked meteorites and synthetic tetragonal majorites is attributed to the faster cooling rate in natural samples.

Original languageEnglish (US)
Pages (from-to)7-14
Number of pages8
JournalEuropean Journal of Mineralogy
Volume14
Issue number1
DOIs
StatePublished - 2002
Externally publishedYes

Keywords

  • Majorite
  • Modulated structure
  • Phase transition
  • TEM
  • Twinning

ASJC Scopus subject areas

  • Geochemistry and Petrology

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