Structure and metamorphism of Penfold Creek area, near Quesnel Lake, central British Columbia

The Quesnel Lake area lies within the Omineca Crystalline Belt, and is underlain by the northern extremity of the Shuswap Metamorphic Complex. Closely spaced and steeply dipping isograds mark the margins of the metamorphic belt. In the Penfold Creek area only one and a half miles separate the biotite and sillimanite isograds. Related to this sharp increase in metamorphic grade there is a marked change in the fold style from similar folds, showing a strong axial-plane cleavage, in the chlorite zone to tight refolded isoclines in the sillimanite zone. Three periods of deformation and two periods of prograde metamorphism have been recognized, with the first metamorphic period being associated with Phase 2 deformation and the second being post Phase 2. Mineralogical changes in pelitic and calcareous assemblages suggest that the increase in metamorphic grade was a function of both temperature and composition of the fluid phase, and that total pressure remained relatively constant. Compositional variations of major minerals in the pelitic rocks are consistent with a model of increasing P[sub H₂O] with increasing temperature, moreover they suggest that in the highest grades of meta-morphism P[sub H₂O] = P[sub Total]. An isoclinally folded granitic gneiss crops out along the shores of Quesnel Lake. It is believed to represent a metamorphosed granite sill which had been intruded into the surrounding Proterozoic sediments.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat