Extended Data Fig. 5: THERMOCALC pressure–temperature pseudosections of the incremental model components after KR4003 with spinel enabled.
From: Deep, ultra-hot-melting residues as cradles of mantle diamond
a, Ext1. b, Ext2. c, Ext2.5. Progressively more refractory compositions show increased spinel stability up to almost 7 GPa in Ext2.5, albeit at very low modal abundances (<0.007 at 5 GPa). Below 7 GPa, spinel replaces garnet or orthopyroxene as the last phase to coexist with olivine and melt. This unexpected high-pressure-stability spinel is attributed to increased MgO and Cr2O3 in the residue (over)stabilizing picrochromite in THERMOCALC21 (see Methods for more details). The effect on Cr2O3 in garnet is only observed close to garnet exhaustion, in which Cr-rich garnet (<13 wt% Cr2O3) converts to a spinel structure.
