2.0 to 1.9 Ga large igneous province magmatism in northern Quebec — U-Pb geochronology and geochemistry

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Kastek, Nico




The northeastern margins of the Superior craton contain the Cape Smith belt and the Labrador Trough (including the Roberts Lake Syncline), which range from 2.2 to 1.9 Ga in age. This thesis examines the age of the Cape Smith belt, its correlation to other units of similar age and its possible extent to the southeast.

Seven U-Pb ages on magmatic baddeleyite and zircon and 84 geochemical analyses were obtained of magmatic units throughout the Cape Smith belt. The most precise are two ages each for the Povungnituk and Chukotat Groups.

The Povungnituk Group yields ages of 1998±6 Ma and 1967±7 Ma. The older age represents the main volcanic pulse, and matches previously obtained U-Pb ages for the Watts Group (Purtuniq) ophiolite of the northern Cape Smith Belt and the Minto and Lac Shpogan dyke swarms that intrude the Superior craton to the south. They define a large igneous province (LIP), extending over an area of >400,000 km2, herein defined as the Minto-Povungnituk LIP.

The Minto-Povungnituk LIP can be divided into two spatially separate geochemical domains with different mantle source characteristics that can be produced in two ways: (1) melting of different portions of Superior craton lithosphere; or (2) two distinct deep mantle sources that remained separated within the ascending plume.

A feeder dyke of the Chukotat Group yielded a U-Pb age of 1874±3 Ma, representing the younger end of its age range. An age obtained from the top of the Chukotat Formation yielded 1861±28 Ma and confirms the previously geochemistry-based interpretation that the Chukotat Group represents a single event.

To the southeast of the Cape Smith belt, the Roberts Lake Syncline hosts two Paleoproterozoic mafic magmatic sequences but their correlation with the units of Labrador Trough to the south, or the Cape Smith belt to the north is uncertain. 94 geochemical analyses were obtained on the two volcanic units and the data show a closer match to the chemical stratigraphy observed within the Cape Smith belt, suggesting that the Roberts Lake Syncline is the easternmost portion of the Ungava Orogen rather than the northernmost part of the Labrador Trough.






Carleton University

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Earth Sciences

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Theses and Dissertations

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