Fig. 3: Metamorphic \(f_{\mathrm{O}_2}\).
From: Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks
Values were calculated thermodynamically using coexisting mineral compositions measured with an electron probe microanalyser. HM, haematite–magnetite reaction; HIR, haematite–ilmenite–rutile reaction. The other reaction symbols are defined in the Methods. Red symbols are assemblages in garnet interiors and blue symbols are assemblages in matrix and/or garnet rims. The vertical red shaded band shows the approximate range of arc magma ΔFMQ values4,5. The grey arrows denote \(f_{{{{\mathrm{O}}}}_2}\) decrease during metamorphism. Italic sample types on the left denote those preserving evidence for synmetamorphic reduction (Fig. 2). Min denotes a minimum \(f_{{{{\mathrm{O}}}}_2}\) estimate. Calculations were done at Cycladic pressure–temperature conditions of 500 °C and 1.5 GPa, except for sample (2), for which 400 °C and 1.0 GPa were used. The \(f_{{{{\mathrm{O}}}}_2}\) corresponding to \(f_{{{{\mathrm{H}}}}_2{{{\mathrm{S}}}}} = f_{{{{\mathrm{SO}}}}_2}\) isofugacity is shown for 500 °C and 1.5 GPa and for subarc conditions of 700 °C and 3.0 GPa. Orange-to-yellow background shading represents an increase in oxygen fugacity from left to right. The ±1σ standard deviation (SD) uncertainty on the oxygen fugacity estimates is shown in the legend. See Methods for calculation details and sample descriptions, and Supplementary Table 1 for ΔFMQ values.
