Fig. 2
From: Reduced and unstratified crust in CV chondrite parent body
Oxygen fugacity vs. temperature plot of the stability field of hedenbergite and andradite. Both single phases: andradite and/or hedenbergite, are stable over a range of log fO2 and T, and poorly constrained their conditions of formation17. Nevertheless, this thermodynamic framework is consistent with the present subdivision of CV3 chondrites into andradite-bearing oxidized (CVOx) and kirschsteinite-bearing reduced (CVRed) subgroups and their inferred different conditions of formation. When the two phase assemblage andradite + hedenbergite is considered, the redox conditions of formation of the Ca-Fe-rich secondary phases could be a bit more restricted but the temperature remains still poorly constrained. Low silica activity of CV3 chondrites is an overlooked key parameter controlling the stability field of the Ca-Fe-rich secondary phase assemblages: the gray arrow indicates the effect of decreasing the silica activity of the system on the stability field of andradite
