Figure F32. Anhydrous major element compositions of hydrothermally altered peridotite samples from Sites 1268, 1270, and 1271 compared to anhydrous compositions of end-member minerals (speciation as for Fig. F23). Tick marks along the vector connecting olivine and pyroxene indicate variations in normative orthopyroxene (opx) content in terms of weight percent orthopyroxene/(orthopyroxene + olivine), assuming olivine Mg# = orthopyroxene Mg#. Most serpentinized dunites and harzburgites from Site 1271 have <30 wt% normative orthopyroxene and so do not require metasomatic increases in Si/(Mg + Fe) during alteration. Substantial divergence of the Site 1271 peridotite compositions from the MgO + FeO to SiO2 mixing line is due to the presence of interstitial gabbroic material, originally including plagioclase and/or igneous amphibole, especially in the impregnated dunite sample. Site 1270 dunites also include relatively abundant Cr-Al spinel.

Figure F32. Anhydrous major element compositions of hydrothermally altered peridotite samples from Sites 1268, 1270, and 1271 compared to anhydrous compositions of end-member minerals (speciation as for Fig. F23). Tick marks along the vector connecting olivine and pyroxene indicate variations in normative orthopyroxene (opx) content in terms of weight percent orthopyroxene/(orthopyroxene + olivine), assuming olivine Mg# = orthopyroxene Mg#. Most serpentinized dunites and harzburgites from Site 1271 have <30 wt% normative orthopyroxene and so do not require metasomatic increases in Si/(Mg + Fe) during alteration. Substantial divergence of the Site 1271 peridotite compositions from the MgO + FeO to SiO₂ mixing line is due to the presence of interstitial gabbroic material, originally including plagioclase and/or igneous amphibole, especially in the impregnated dunite sample. Site 1270 dunites also include relatively abundant Cr-Al spinel.