The texture, origin, and emplacement of the granitic rocks of Glenlyon range, Yukon, Canada

Abstract

In Glenlyon range the older pre-intrusive rocks include quartzo-feldspathic schists (Ambibolite facies) with minor carbonate and lime-silicate rocks of the Yukon group overlain by a succession of limestones and slates and phyllites (green schist facies) of the Harvey Group. These rocks form the north limb of an east-west trending anticlinorium. The Drury quartz monzonite is intruded into the axial region of the anticlinorium. This mass grades continuously from a biotite granodiorite core to an outer zone of quartz monzonite in which the proportions of hydridized inclusions and septa of metamorphic rock increase with complete gradation to the granite-free metamorphic host terrane. To the north and east a second large mass, the Peak granodiorite, identical with the core of the Drury quartz monzonite, has been emplaced with clearly crosscutting intrusive relations. A pattern of large scale faulting associated with the contact of the Peak granodiorite suggests that fault block movement may have provided some of the intrusive space requirements. Smaller alaskite dikes cut both the metamorphic complex and the Drury quartz monzonite. Detailed petrographic studies of the textures and mineral modes of the granitic rocks argue for a similar crystallization history of the Peak granodiorite and the core of the Drury quartz monzonite. The textural evidence for paragenesis and the mineral composition trends of the entire intrusive complex are combined with discussions of the crystallization of a hypothetical granodiarite magma based on available experimental data of the system KAlSi3O8 - NaAlSi3O8 - CaAl2Si2O8 - SiO2 - H2O. All of the significant natural paragenetic relations, particularly the important role of potash feldspar (including replacement reactions) in the later crystallization stages, can be explained as resulting from magmatic crystallization. These effects are distinguished from metasomatic phenomena in the host rocks. The validity of such arguments rests in part on a detailed analysis of the sampling of these granitic masses and problems of representation of modal data. The results of approximately 150 modal analyses are presented in four mineral-component tetrahedrons to support these discussions.