Figure F13. A. Anhydrous major element compositions of hydrothermally altered peridotite samples from Site 1268, plotted in terms of mole fraction of SiO2 vs. mole fraction of MgO + FeO, compared to anhydrous compositions of end-member minerals (speciation is SiO2, TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, with all Fe as FeO). B. Expanded plot of A, with weight percent pyroxene proportions added. Talc-altered peridotites approach the composition of end-member talc. Even serpentinized peridotites have ~25 wt% normative orthopyroxene, indicative of substantial addition of SiO2 and/or loss of MgO + FeO. Slight divergence of the peridotite compositions from the MgO + FeO to SiO2 mixing line is due to the minor presence of other oxides, mainly in the form of a few percent Cr-Al spinel in most peridotite samples.
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