Figure F25. Anhydrous major element compositions of hydrothermally altered peridotite samples from Sites 1268 and 1270, plotted in terms of mole fraction of SiO2 vs. mole fraction of MgO + FeO, compared to anhydrous compositions of end-member minerals (speciation as for Fig. F22). Tick marks along the vector connecting olivine and pyroxene are for variations in normative orthopyroxene content in terms of weight percent orthopyroxene/(orthopyroxene + olivine), assuming olivine Mg# = orthopyroxene Mg#. All but two of the serpentinized peridotites from these sites have >30 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.
