Figure 4
Variation in ∆logƒO2 as a function of pressure/depth for samples from this study. Pressure was converted to depth assuming Depth (km) = P (GPa)*32.4. Thin horizontal lines connect ƒO2 values determined from garnet (solid) and spinel (open) equilibria from the same garnet-spinel peridotite xenolith. The dashed line demarcates the occurrences of type A and B garnets with respect to those with type C and D signatures. The grey and yellow fields encompass the depleted and enriched samples reported for the Slave craton (Yaxley et al.41; Creighton et al.42). The thick solid line illustrates the predicted variation for pre-metasomatic (primitive) mantle peridotite along a 40 mW/m2 geotherm from Luth and Stachel38. The position of the graphite-diamond (gr-dia) transition was adopted from Kennedy and Kennedy43. EMOG and EMOD represent the positions of equilibria controlling carbonate stability in harzburgitic bulk compositions: enstatite + magnesite = forsterite + graphite (G) or diamond (D) + O2 from Luth and Stachel38, computed for a 40 mW/m2 geotherm. The black cross in the lower right hand corner illustrates the estimated uncertainties in the ƒO2 and pressure calculations.
