2:30 PM - 2:45 PM
[SIT23-04] Experimental confirmation of a spineloid transitional olivine polymorph using ultrafine-grained aggregates of Mg2GeO4
Keywords:olivine-spinel transition, ω-olivine, mantle, laboratory, metastable, martensitic
The olivine-spinel transition in Mg2GeO4 occurs around 810°C, and all experiments were done in the stability field of olivine. The deformation curves, supported by Raman and XRD data, suggest that ω-olivine, expected by Poirier in 1981, and observed in Mg2GeO4 within a meteorite in 2017, transiently forms during the deformation. ω-olivine is a spineloid metastable olivine, which does not have any stability field in a P-T diagram, but it might have one in a P-T-σ diagram. It was reproduced in the stability fields of β-olivine (Guyot et al., 1991) of γ-olivine (Reynard et al., 1994). Here I show that it can also form in the stability of α-olivine.
It seems that the transition occurs only between 1000°C and 1150°C when the stress approaches 100 MPa, as a result of a competition between diffusional and displacive processes.
The existence of ω-olivine in stressed mantle regardless of stability fields could have major consequences on how we understand the solid-state olivine-spinel transition and related earthquakes triggering. Below 1200°C, if ω-olivine does not form then α-olivine is metastable.