Extended Data Fig. 1: The stable mineral assemblage for a high-pressure serpentinite.
From: Mantle wedge oxidation from deserpentinization modulated by sediment-derived fluids
X(O2)-P/T (along a thermal gradient, see Methods) pseudosection7 for a representative Ca-poor high-pressure serpentinite from CdA (sample Al98-05a35) with sulphur and carbon content from ref. 27 (these values were confirmed by new, duplicate analyses) and ferric iron from this work (see Supplementary Table 1). The vertical line represents the intrinsic deserpentinization for a fixed O2 content of the system (Path I), corresponding to the bulk O2 for sample Al98-05a (15.602 mol/kg is used instead of the measured 15.672 mol/kg for better agreement with the observed sequence of mineral assemblages at CdA; it likely reflects the amount of ferric iron in antigorite, not accounted for in the available solid solution models89). The horizontal path (IIa) shows schematically the evolution if the system is externally infiltrated by fluids equilibrated with metasedimentary rocks with a high reducing capacity (graphite-bearing metapelite). The quantitative evolution along path IIa is shown in Fig. 3b in the main text (see also Supplementary Figure 6 for the evolution of the speciation in the fluid). Path IIb corresponds to the prograde evolution after the graphite metapelite-infiltrated deserpentinization potentially followed by CdG.
