POSSIBLE CORE COMPLEX SOUTH OF THE PRIEST RIVER COMPLEX IN BONNIE LAKE, EASTERN WASHINGTON

An island of schistose Precambrian Belt Supergroup pelitic basement rock is exposed at Bonnie Lake, Spokane County, Washington. The rocks composing this island dip west and are folded into inclined to recumbent, gentle to isoclinal folds plunging approximately 30 degrees to the north. Oriented samples were collected and a petrographic analysis was able to identify the confining assemblage of Cordierite-Biotite-Chlorite-Quartz-Sillimanite which indicates P/T conditions of 600-650 degrees C, and 2-4 kilobars of pressure during the metamorphism of this body. These values are comparable to conditions estimated for the Newport Fault Footwall near the Spokane Dome. Therefore, we test the hypotheses that this island represents a southern continuation of a core complex, similar to the Priest River Complex, possibly offset to the west by a continuation of the Lewis and Clarke fault, which currently represents the boundary of the known extent of this body. Future research will investigate the possible presence of a metamorphic core complex located in Bonnie Lake.