Open Collections

Abstract

This dissertation investigates the petrogenesis of the Fir carbonatite system (Monashee Mountains of British Columbia), which is particularly interesting because of its high degree of deformation, the relatively minor presence of associated silicate rocks and its comparably high content of Ta. A detailed examination of the rock textures and microstructures shows that the two main fabrics, a primary gneissic and a secondary fine-grained, foliated fabric, are the results of plastic flow and dynamic recrystallization during deformation. The primary fabric developed under peakmetamorphic conditions and was overprinted by retrograde mylonitic shear zones. The microtextural record and the equilibration temperatures are compared to regional marbles that share the same tectonometamorphic history. Both lithologies reveal a very similar petrological record indicative of metamorphic equilibration, however, some calculated temperatures in the carbonatites (∼700 °C) exceed the peak-metamorphic conditions (620 - 650 °C), which indicates that the magmatic crystallization temperatures are preserved despite amphibolite-facies metamorphism. Apart from minor calcium and sodium amphiboles the Fir system contains predominantly the sodium-calcium amphiboles winchite and katophorite which define two major mineralogical facies. The amphiboles have high F contents (