PETROLOGY AND TECTONIC IMPLICATIONS OF SILURIAN() METAVOLCANIC ROCKS IN THE CLYBURN BROOK AREA AND ON INGONISH ISLAND, NORTHEASTERN CAPE-BRETON ISLAND, NOVA-SCOTIA

Metavolcanic rocks in the Clyburn Brook area of northeastern Cape Bret on Island range in composition from mafic to felsic, include flows and tuffs, and are interlayered with less abundant semi-pelitic metasedim entary rocks. In contrast, metavolcanic rocks on nearby Ingonish Islan d are mainly rhyolitic flows and tuffs, and lack interlayered metasedi mentary rocks. Because correlation between these two areas cannot be c onfirmed without more radiometric dating, continued use of separate na mes (Clyburn Brook formation and Ingonish Island rhyolite) is advocate d. Rocks in the Clyburn Brook formation contain greenschist facies min eral assemblages and are mainly well foliated. Although also metamorph osed, the Ingonish Island rhyolite is mainly unfoliated, and the metam orphism may be a result of contact metamorphism. A contact metamorphic overprint is also present in the Clyburn Brook formation adjacent to the ca. 402 Ma Cameron Brook Granodiorite, and felsic dykes perhaps re lated to the intrusion occur in both the Clyburn Brook formation and t he Ingonish Island rhyolite. These observations suggest that both unit s are older than ca. 402 Ma, consistent with a previously published im precise Rb-Sr date of 412 +/- 15 Ma for the Ingonish Island rhyolite. Petrochemical characteristics of mafic rocks in the Clyburn Brook form ation indicate tholeiitic affinity and origin in an are-related settin g, possibly a back-are. Although they show chemical differences, felsi c rocks in both the Clyburn Brook formation and on Ingonish Island hav e compositions consistent with an extensional setting, possibly within a continental are or back-are such as the modern-day Taupo volcanic z one in New Zealand. Overall, the Clyburn Brook formation shows litholo gical and chemical similarity to the Money Point Group, a Silurian (ca . 430 Ma) volcanic are/back-arc unit in the Aspy terrane of Cape Breto n Island, and is inferred to be of similar age.