Coronite Amphibolites from the Whitestone Area, Parry Sound, Ontario

Abstract

<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>