Contact metamorphism in the Kwoiek area of British Columbia; an end member of the metamorphic process

Compositional zoning in garnets from this high-pressure contact metamorphic area is a result of depletion of the constituent elements of garnet from a homogeneous matrix, the composition of which thus changes when the garnet grows. Garnet, as well as staurolite, and possibly ilmenite that do not equilibrate internally are termed 'refractory' phases. Biotite, chlorite and muscovite equilibrate in response to changing external condition and thus form a matrix. Differences between measured electron microprobe profiles of garnet and those calculated from a depletion model are due mainly to the effect of Mn on the Mg/Fe ratio in the garnet and partly to changing relative proportions of chlorite, muscovite and biotite during the growth of the garnet. Higher grade assemblages seem to have bypassed the lower grade assemblages; they grew at nearly constant temperature.