Renee‑Luce Simard

This thesis presents geochemical and volcanological studies of two late Paleozoic sequences of the pericratonic Yukon-Tanana terrane of the northern Canadian Cordillera, the Mississippian to mid-Pennsylvanian Little Salmon formation and the Mississippian to Permian Klinkit Group. It provides insights that unravel the tectonic evolution of the western margin of Laurentia in late Paleozoic time.

Rocks of the Little Salmon formation are well exposed in central Yukon. The lower part of the Little Salmon magmatic sequence consists of Mississippian quartz-feldspar phyric felsic rocks. These calc-alkaline rocks probably represent high-level intrusions formed by crustal melting in a continental arc setting, the Little Kalzas-Little Salmon arc. Conformably overlying these felsic rocks is a thick pile of asthenosphere-derived alkali basalts (-Nd=+7.5) showing both proximal and distal volcanic lithofacies. It records seamount formation atop an extensional synvolcanic fault associated with the development of a rift basin(s) during the rifting of the Little Kalzas-Little Salmon continental arc system. This rifting resembles that of the modern Izu-Bonin-Mariana arc and the proto-Japan island arc extension and thinning.

The Klinkit Group is well exposed in northern British Columbia and southern Yukon. It is characterized at its base by a thick Mississippian to Early Pennsylvanian carbonate unit and overlain by abundant Permian primitive arc-derived volcaniclastic rocks (-Nd+6.7 to 7.4). These thick volcaniclastic sequences represent megaturbidite deposits emplaced in a subsiding basin near active volcano(es), the Klinkit arc. Localized alkali basalts suggest intra-arc rifting event(s). The Klinkit Group closely resembles the basement of the Mesozoic Quesnel arc terrane; however, it also has characteristics similar to sequences of the pericratonic Yukon-Tanana terrane. The similarity suggests that the basement of the Mesozoic arc of the Quesnel terrane is the pericratonic Yukon-Tanana terrane or its southern equivalent.

Tectonic pulses along the late Paleozoic western margin of Laurentia have been driven by oblique continent-continent collisions on the other margins of the continent, first in Late Silurian-Early-Devonian time, then in Carboniferous time. These collisions affected the translation and rotation of Laurentia, forcing plate boundary reorganization along its west margin, hence controlling the formation and tectonic evolution of the pericratonic systems throughout late Paleozoic time.

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Pages:198
Supervisor: Jarda Dostal