Abstract

Major and minor element microprobe analyses were obtained for plagioclase, olivine, augite, and hypersthene in a suite of rocks from 2.2 km of stratigraphy at Windimurra Hills toward the east of the Windimurra Complex. The Windimurra Hills section is a repetitive sequence of lithologies dominated by anorthosites, troctolites, gabbronorites, and olivine-gabbronorites. The constituent phases exhibit a limited range of major element compositions throughout the succession, i.e. (mean per sample), olivine = Fo (sub 67-56) ; augite (MgO/MgO + FeO) = 76-70; hypersthene (MgO/MgO + FeO) = 70-65; plagioclase = An (sub 79-72) . Minor element concentrations (wt %) in the mafic silicates are as follows: Ni in olivine = 0.22-0.03; Cr in augite = 0.17-0.03; Cr in hypersthene = 0.09-0.02. Variations in compositions with stratigraphic height are irregular and the complete ranges in compositions are locally expressed over the smallest sampling interval. There is a slight trend toward iron enrichment in the mafic silicates upward through the section. Both major and minor element concentrations display a subtle change in trends above the first appearance of significant cumulus Ti magnetite about halfway through the section.Comparisons with data for the Stillwater Complex suggest that, apart from the absence of magnetite at Stillwater, the Windimurra Hills section is a sequence similar to the Middle Banded series.

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