Petrology and Geochemistry of Some Igneous Intrusives in the Back River Volcanic Complex, District of MacKenzie, Northwest Territories

Abstract

Granitic intrusives and a zoned gabbroic dyke situated within the Back River Volcanic Complex were mapped and studied. Petrography and geochemical analyses were performed on selected specimens. Chemican variation diagrams suggest that the granites may have been derived from the fractional crystallization of a single parent magma. In order of decreasing age, these granitic units are defined as follows: 1. Hornblende Quartz Syenite 2. Granite 3. Quartz Monzodiorite A zoned gabbro/quartz gabbro dyke cuts the granites. Pyroxene and plagioclase are the dominant minerals of this dyke, and are found to vary antipathetically throughout the central portions of the dyke. Chemical studies of this system suggest that the zoning may be the result of a series of multiple injections from different source magmas.