Phase transitions in orthopyroxene (En90) to 49 GPa from single-crystal X-ray diffraction

摘要: Abstract Synchrotron-based high-pressure single-crystal X-ray diffraction experiments were conducted on ∼Mg0.9Fe0.1SiO3 (En90) orthopyroxene crystals at room temperature to a maximum pressure of 48.5 GPa. The sample was compressed in diamond anvil cell with neon pressure-transmitting medium and gold calibrant. In addition the previously described β-opx transition (designated HPCEN2 previous studies), we observe two further phase transitions 29.9 GPa 40.3 GPa. However, do not γ-opx recently an Fe-rich composition. structures both new phases solved space group Pca21. While their Mg–O layers remain pyroxene-like, Si–O transform stepwise fashion akimotoite-like sheets, sites 4-, 4+1-, or 6-fold coordination, depending specific structure layer. Due increased coordination number, designate α- β-post-orthopyroxene (α-popx β-popx). α-popx has one layer that is entirely tetrahedral, contains tetrahedra 4+1-coordinated Si distorted square pyramids. β-popx retains mixed 4- found α-popx, while other adopts fully octahedral coordination. show progressive transformation towards arrangement akimotoite, potentially important earth’s zone. Metastable transformations pyroxenes are interest for understanding possible metastability geological environments such as subducting slabs meteorite impacts.