Euhedral or subhedral orthopyroxene (0.5-2.0 mm) occurred as isolated crystals or glomeroporphyritic aggregates, displaying bronzite ([En.sub.82-86]) or hypersthene ([En.sub.64-79]) core compositions (Table 5 in Appendix A Supplementary Material, and Fig.
These lines of evidence include: (a) chilled magmatic enclaves which probably represent the material that mingled with felsic magma, causing thermal and compositional disequilibrium; (b) presence of more and less silicic amphiboles in the same sample, some of them showing reaction textures and inverse zoning; (c) bronzite and hypersthene orthopyroxenes displaying augitic reaction rims, and (d) sieved plagioclase crystals and their occurrence together with clear normal plagioclase, as well as oscillatory zoning of sieved plagioclase.
Using the electron microprobe technique, it was found that the measured value for Cr in the Smithsonian hypersthene
was 0.53 [+ or -] 0.02 (standard deviation) mass fraction % (compared to the nominal value of 0.51 %).
These volcanics are quartz normative (6.83-10.00%) with dominant normative plagioclase (43.88-56.41%) and sub-ordinate normative hypersthene
In general, the obtained crystallisation sequences are rather similar to the real ones observed in the studied rocks; the presence of orthopyroxene in the model (not recognised in the rocks) is probably related to the high [Al.sub.2][0.sub.3] contents of the rocks and is coherent with their normative hypersthene
The most fundamental characteristic of tholeiites is the presence of a low-Ca pyroxene (e.g., hypersthene
), most commonly in the matrix, locally as phenocrysts (Fig.
All are hypersthene
normative and show relatively high contents of Ti[O.sub.2] (2.3-3.4 wt%) and high [P.sub.2][O.sub.5] (1.4-2.1 wt%).
Petrographic examination and microprobe analyses of the ultramafic rocks within the Greendale Complex show that they contain tschermakitic hornblende (magnesiohastingsite) which poikilitically encloses olivine, hypersthene
, clinopyroxene (augite, endiopside, diopside), and chromite.
is faintly coloured and pleochroic from pale green to pale reddish brown.
Petrological studies of lava flows show several varieties of andesites and dacites, which include hypersthene
, hornblende, lamprobolite andesites and hornblende biotite dacite.