GEOLOGY OF THE KITLOPE LAKE AREA, COAST MOUNTAINS, BRITISH COLUMBIA

The Kitlope pluton is an early Tertiary granodiorite that intruded into migmatitic gneissic country rocks near the southern termination of the central gneiss complex of the Coast Mountains of British Columbia. The pluton is located east of the Coast shear zone and has near vertical east-west contacts. The Kitlope pluton is composed predominately of calc-alkaline granodiorite. The primary mineralogy is quartz, plagioclase, k-feldspar, biotite, and sometimes hornblende; the accessory phases include titanite, apatite, magnetite, zircon, and allanite, which is sometimes rimmed by epidote. The intrusion consists of discrete sheets of granodiorite interrupted by screens of gneissic country rock. The pluton varies from foliated to non-foliated, with the strongest solid-state foliations occurring near contacts and country rock screens. In many places the foliation is concordant with country rock fabrics, but in some places the pluton crosscuts fabrics, attesting to deformation prior intrusion of the pluton. Fabrics within the pluton show a complete transition from solid-state foliations near the contacts to magmatic foliation in the interior, which demonstrates the syntectonic nature of the pluton. Foliations vary from NW-SE along its western side to almost E-W at Mount Blane to the east, with consistent steep to subvertical dips. Mineral lineations within the pluton and its country rocks are variable but generally plunge steeply. Isoclinal folds in the country rock and within screens and consistent reverse kinematic indicators demonstrate shortening across the margins of the pluton during emplacement. Pressures at which the Kitlope pluton intruded were calculated using Al-in-hornblende barometry in 3 samples, which give pressures 6.8, 7.0 and 7.1 kbars. Ten temperatures for the pluton and country rocks were calculated using the hornblende-plagioclase thermometer and range from 642-756° C. These pressures and temperatures are similar to those obtained from locations to the north at Douglas Channel and the Skeena River, which suggests that the central gneiss complex extends at least as far south as the northern margin of the Kitlope pluton.