Tyson Brown

B. Sc. (Advanced Major) Thesis

⁴⁰Ar/³⁹Ar investigation of the Kanairiktok Shear Zone, Makkovik Province, Labrador

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The Kanairiktok shear zone forms a dextral transtensional structural boundary between the Hopedale Block of the Archean Nain Province and Paleoproterozoic Kaipokok Domain of the Makkovik Province. This study employs ⁴⁰Ar/³⁹Ar analysis of 6 hornblende and 5 muscovite samples to document timing of the low-grade greenschist facies movement along the Kanairiktok shear zone and the thermal histories of the Hopedale block and Kaipokok Domain, which lie to either side of the shear zone. Results can be classified into three general categories. (1) Samples from the Hopedale Block show no disturbance from the metamorphic events of the Makkovikian orogeny. The 2617 ± 23 Ma (hornblende) and 2425 ± 8 Ma (muscovite) cooling ages illustrate a simple post-Archean thermal history. (2) The hornblende and muscovite samples from the Kaipokok Domain and Kanairiktok shear zone provide a wide range of ages with variable spectral disturbance (ca. 1751-2023 Ma). Disturbed spectra within this category can be attributed to mixed phases, excess argon, and partial resetting of argon systems. The variable spectral disturbances are the result of two amphibolite and one greenschist facies deformation/metamorphic events within the Kaipokok Domain and Kanairiktok shear zone. (3) Interpreted Paleoproterozoic syn-tectonic muscovite samples from the Kainariktok shear zone give ages of 1696 ± 8 Ma and 1691 ± 12 Ma These ages suggest that the low-grade greenschist facies movement resulted from reactivation of the Kanairiktok shear zone. This is interpreted to be the result of indentation of Laurentia by the accretion of a hypothetical Labradorian terrane, analogous to the reactivation of Paleozoic suture during the Cenozoic Indian-Eurasian collision.

Keywords: ⁴⁰Ar/³⁹Ar, Kanairiktok shear zone, Makkovik Province, Muscovite, Hornblende, Deformation, Labradorian orogeny, Indentation
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Supervisor: Nicholas Culshaw