IMPLICATIONS OF THE EAST LAKE DYKE FOR THE NATURE OF THE CONTACT BETWEEN THE POVUNGNITUK AND CHUKOTAT GROUPS OF THE CAPE SMITH FOLDBELT, UNGAVA, QUEBEC

Recent fieldwork in the Cape Smith Foldbelt has identified a conformable contact between the Povungnituk Group of volcanic and sedimentary rocks and Chukotat Group of komatiitic to tholeiitic basalts. Previous work by St. Onge and Lucas (1993) in the Foldbelt had indicated the presence of regional thrust faults separating the two groups. However, in the area of East Lake, the contact is cut by a large (300m) peridotite dyke of the Chukotat Raglan Formation. The northeast trending dyke crosscuts Povungnituk lavas and sediments derived from them as well as the overlying siltstones which mark the boundary to the Chukotat. This dyke has been identified as a feeding conduit to the Chukotat lavas above the sediment layer based on a correlation between marginal dyke pyroxenites and initial Chukotat lava compositions, an interpretation that is supported by the physical relationships within the complex and volcanological features in the Chukotat lavas indicating the area as a point of extrusion. Although Chukotat dykes are not common in the Cape Smith Foldbelt, the fact that the East Lake dyke intrudes the Povungnituk volcanics and sediments has important implications for the tectonic relationship between the Chukotat and Povungnituk Groups, as well as the prospectivity of the numerous peridotite sills in the Povungnituk Group for sulphide mineralization.