3h) is made up of plagioclase, hornblende, augite,
orthopyroxene, quartz, magnetite, titanite, and apatite.
Orthopyroxene occurs as euhedral, medium- to large-sized grains.
Orthopyroxene compositions range from[Wo.sub.3][En.sub.72][Fs.sub.25] to [Wo.sub.2][En.sub.51][Fs.sub.47].
The more mafic andesite samples of the Ross Island Formation may have formed in a residue containing olivine +
orthopyroxene + clinopyroxene + amphibole [+ or -] plagioclase [+ or -] Fe-Ti oxide.
Within the kimberlites, the following mineral phases were identified: (1) lherzolitic, eclogitic and megacrystal garnet (megacrystal garnet was also found in some of the lamprophyres), (2) clinopyroxene which plots in Fipke's diamondiferous CPX domain (as does one lamprophyre), (3)
orthopyroxene with < 1% to 1.5% [Al.sub.2][O.sub.3], and (4) olivine with Fo contents of ~88-92 (some of the lamprophyres have two populations of olivine with clusters of similar high Fo values).
Shock effects are also present throughout the sample in the form of undulose extinction, irregular and planar fractures, slight mosaic patterns, and planar deformation features in
orthopyroxene.
Major element compositions of olivine,
orthopyroxene, clinopyroxene, plagioclase, amphibole and phlogopite has been analysed directly on polished thin and thick (130 [micro]m) sections at the Centro Nacional de Microscopia Electronica (Complutense University of Madrid) using a JEOL JXA-8900 M electron microprobe with four wavelength-dispersive spectrometers.
The minerals of these rocks consists of olivine, clinopyroxene,
orthopyroxene and chrome- spinel that have mesh and granular texture that altered to serpentine minerals and iron-oxid (Fig.
In the lowermost part, the metagabbro contains hornblende + clinopyroxene +
orthopyroxene + plagioclase [+ or -] quartz mineral assemblage indicating granulite-facies metamorphism.
They generally show a mineralogical assemblage of plagioclase + amphibole +
orthopyroxene [+ or -] clinopyroxene [+ or -] quartz + Fe-Ti oxides.