Figure F22. Anhydrous major element compositions of gabbronorite samples from Hole 1270B, plotted in terms of oxide mole fractions (mole fractions calculated for SiO2, TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, with all Fe as FeO). Calcic amphibole end-members are tremolite/actinolite, hornblende, edenite, pargasite, and tschermakite. Chlorite end-member is clinochlore. The bold triangle encloses possible pyroxene gabbro and gabbronorite assemblages with calcic plagioclase. All of the Hole 1270B gabbronorites lie outside this triangle, indicating that they must have contained substantial proportions of igneous olivine (dashed lines) and/or Fe-Ti oxides (thin lines). Olivine could have been consumed by subsolidus or near-solidus oxidation reactions that produced pyroxene + magnetite. However, the high Ti contents of all Hole 1270B gabbronorites require substantial proportions of normative ilmenite and/or magnetite, so it is very likely that these rocks all contain igneous Fe-Ti oxides.
Next Figure | Table of Contents