Figure F41. Anhydrous major element compositions of hydrothermally altered peridotite samples from Sites 1268, 1270, 1271, and 1272, 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 Figure 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#. Most serpentinized dunites and harzburgites from Site 1272 have <25 wt% normative orthopyroxene and so do not require metasomatic increases in Si/(Mg + Fe) during alteration. Substantial divergence of two Site 1272 peridotite compositions from the MgO + FeO to SiO2 mixing line is due to the presence of carbonate alteration in veins and perhaps also in the serpentinite matrix.
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