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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Geology

Supervisor

Osinski, Gordon R.

Abstract

The northernmost exposure of the Laurentian shield in Canada outcrops on Devon and Ellesmere islands within the Canadian Arctic Archipelago. Due to the remote location, the basement rocks of these islands have received little attention. From this study, zircon crystallization ages demonstrate that Devon Island is underlain by a late Neoarchean terrane comprising orthogneisses emplaced at ca. 2.55–2.51 Ga and an interleaved metasedimentary sequence deposited at ca. ≥2.47 Ga. On northern Devon Island, younger metasedimentary sequence(s) were deposited at ca. 2.2–1.9 Ga and intruded by ca. 2.01–1.95 Ga granitoids. Devon and Ellesmere islands experienced widespread metamorphic activity associated with the Thelon orogeny between ca. 1.95–1.87 Ga, peaking at ca. 1.91 Ga. Minimum peak temperatures of metamorphism are estimated at ca. >800 ℃ throughout Devon and Ellesmere islands and the first documented sapphirine + quartz assemblage in the Devon and Ellesmere islands area is diagnostic evidence of ultrahigh temperature conditions (>900 ℃). The abundance of spinel + quartz (ca. ≥940 ℃) metasedimentary rocks on Ellesmere Island likely provides further evidence of widespread ultrahigh temperature conditions. Peak pressures of ca. 1.9 Ga metamorphism are estimated at ca. 9 kbar on southern Devon Island and ca. 6–7.5 kbar for northern Devon and Ellesmere islands. Earlier, poorly constrained metamorphic events are recorded at ca. 2.54, 2.47 and 2.30 Ga, possibly associated with pulses of the Arrowsmith orogeny. The late Neoarchean Devon terrane potentially extends to the southwest on Boothia Peninsula and to the northeast in the Prudhoe Land area of northwestern Greenland. The juvenile middle Paleoproterozoic rocks of northern Devon and Ellesmere islands represent a northern extension of the Thelon tectonic zone, which we term the Ellesmere tectonic zone.

Summary for Lay Audience

The Canadian shield is exposed from southern Ontario to the northern reaches of the Canadian Arctic Archipelago in Nunavut. The Canadian shield is made up of metamorphic rocks that are one to four billion years old and are separated into several geologic provinces that have been merged through plate tectonic processes over billions of years.

This study focuses on the northernmost shield rocks in Canada, which are exposed on Devon and Ellesmere islands in the Canadian Arctic Archipelago. Due to the remote location and the mostly absent human population of these islands, the shield rocks have received minimal previous research compared to other areas of the Canadian shield. To expand our knowledge of the multi-billion-year geologic history of these islands, we use rock dating and pressure–temperature modelling techniques to determine when these rocks were formed, when they were involved in metamorphic events, and what pressures and temperatures they experienced during these metamorphic events.

Results demonstrate that the shield rocks on Devon Island were formed around 2.5 billion years ago, while the shield rocks on Ellesmere and some on northern Devon Island were formed around 2.1 to 1.9 billion years ago during the merging of geologic provinces. This merging of geologic provinces would have caused the formation of a mountain range and the underlying rocks were subjected to metamorphism with temperatures reaching >800 ℃. The discovery of a rock containing the minerals sapphirine + quartz, which only form together at very high temperatures, suggests that temperatures of metamorphism were locally >900 ℃.

Comparing the shield rocks on Devon and Ellesmere islands to other shield rocks in the area suggests that the shield rocks on Boothia Peninsula and northwestern Greenland may share the same multi-billion-year geologic history as Devon and Ellesmere islands.

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