<p> Coronite amphibolites located near the western contact of the. Whitestone Lake Anorthosite were studied in the field and laboratory in order to determine their origin. The corona textures consisted of garnet cores surrounded by complete rims of plagioclase, which in turn were occasionally surrounded by partial or complete rims of garnet or pyroxene. The development of coronas is also accompanied by an increase in pyroxene in the rock, and the development of cryptic zoning in both garnets and plagioclases. Whole rock X-Ray Fluorescence and mineral electron-probe analyses were determined for suites of samples collected. The analyses suggest that corona development occurred isochemically as the result of a contact metamorphism induced by anorthosite emplacement and mineral reactions have been proposed. Microprobe analyses of the garnets led to the establishment of models for the production of garnets in mafic assemblages and models for the observed cryptic zoning in the garnets~ It was concluded that the coronites represent the transition from almandine amphibolite facies to clinopyroxene subfacies of granulite metamorphism of garnetiferous amphibolites. This transition results from the thermal metamorphism induced by the emplacement of the Whitestone lake anorthosite. </p> / Thesis / Doctor of Philosophy (PhD)

The conclusions of this thesis rest on comprehensive geological, chemical and petrographical analyses of both the Whitestone anorthosite and the contiguous rocks. The anorthosite is believed to have been intruded as a magma of anorthositic composition just after the acme of the last regional metamorphism. Various textural and mineralogical features, ostensibly metamorphic, are interpreted as being due to an extravagantly long magmatic end-game. / Thesis / Doctor of Philosophy (PhD)

<p> The Whitestone Anorthosite is a relatively small anorthosite body (160 km2 ) located within the Parry Sound structural domain, Western Grenville Province, Ontario. Both the anorthosite and the surrounding gneisses have been affected by a granulite grade metamorphic event which predates the Grenville Orogeny. The outer margin of the anorthosite body has been strongly deformed and recrystallized and is characterized by a pervasive metasomatic alteration consisting of garnet, scapolite, hornblende, apatite, biotite, sphene, carbonate and opaques. The country rock gneisses exhibit a corresponding discontinuous, and highly variable, reaction aureole. Pre-existing mafic gneisses are particularily affected, being characterized by the breakdown of orthopyroxene and hornblende, an increase in garnet, clinopyroxene, apatite and opaques, and enrichment in Fe, Ti and P. </p> <p> The metasomatic alteration exhibited by the Whitestone Anorthosite is thought to be due to a combination of two processes: 1. Mechanical mixing at the anorthosite/country rock contact during intense deformation (tectonic assimilation), and 2. Widespread absorption of mobile components (predominantly volatiles) from both included material and the surrounding gneisses. </p> <p>The formation of the country rock reaction aureole is a continuous solid state metamorphic process, whereby mobile components are preferentially leached from the rock leaving a mafic restite. Post-deformation cooling of the anorthosite, combined with an increased volatile flux, has imparted a polygonal mosaic texture suggestive of contact metamorphism. The typical garnet-clinopyroxene assemblage exhibited by mafic gneisses within the reaction aureole, is a consequence of the increased Fe/Mg ratio which stabilizes this assemblage at lower P, T conditions. The temperature of final equilibration and recrystallization is estimated to be 750 ± 70 °C, based on clinopyroxene-garnet geotherrnometry. </p> <p> A similar metasomatic interaction, to the one outlined in this thesis, is to be expected at all anorthosite/country rock contacts which have been overprinted by granulite metamorphism. </p> / Thesis / Master of Science (MSc)