Reconnaissance geology of the Precambrian Shield of Ellesmere, Devon and Coburg islands, Canadian Arctic Archipelago

The extensively ice- and snow-covered highland areas of southeastern Ellesmere Island, eastern Devon Island and Coburg Island are underlain by highly deformed granulite facies rocks of the northernmost Canadian Shield. The bulk of the terrane comprises a late Archean or early Proterozaic continental margin sequence now made up of garnet-sillimanite-cordierite gneiss, marble, quartzite, quartzafeldspathic gneiss of calc-alkaline composition, and metabasalt chemically of oceanic affinity, in interleaved belts trending northerly on Ellesmere and Coburg islands, easterly on Devon Island. These rocks were intruded by a granitoid suite under granulite facies conditions between I.9 and 2. 0 Ga. Orthopyroxene-bearing tonalitic to granitic rocks, retrograded to varying degree, form especially extensive terranes in the southern and northern parts of the shield on Ellesmere Island. Xenolithrich peraluminous granite with garnet, cordierite and/or sillimanite is abundant on Ellesmere Island. Most, if not all, of the intrusions are thought to have originated by crustal anatexis related to the granulite facies metamorphism and are moderately to strongly deformed. Pressures and temperatures of metamorphism range from 7 to 3 x I 05 kPa and about 750 to 500°C, largely reflecting decompression and cooling during uplift. Pressures recorded in Devon Island rocks are generally higher than elsewhere in the map area. The interleaving of belts of diverse lithologies, the high metamorphic grade, and significant partial melting are probably due to crustal thickening by thrust stacking, possibly resulting from continental collision. The crystalline rocks are overlain on the east coast of Ellesmere Island by unmetamorphosed sediments and basalts of the Neohelikian Thule Group and are bordered on the west and north by lower Paleozaic strata of the Arctic Platform.