Kanairiktok shear zone: the boundary between the Paleoproterozoic Makkovik Province and the Archean Nain Province, Labrador, Canada.

The polyphase Kanairiktok shear zone (KNSZ) separates gneissic rocks of the Archean Nain craton from their reworked equivalents in the Paleoproterozoic Kaipokok domain of the Makkovik Province. In its early stages, the KNSZ bounded the Kaipokok domain as it was thermally softened by 1895-1870 Ma And...

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Bibliographic Details
Published in:Canadian Journal of Earth Sciences
Main Authors: Culshaw, N, Brown, T, Reynolds, P H, Ketchum, J WF
Format: Article in Journal/Newspaper
Language:English
Published: Canadian Science Publishing 2000
Subjects:
Canada
Nain
Makkovik
Harbour Bay
Island Harbour
Online Access:http://dx.doi.org/10.1139/e00-035
http://www.nrcresearchpress.com/doi/pdf/10.1139/e00-035
Description
Summary:The polyphase Kanairiktok shear zone (KNSZ) separates gneissic rocks of the Archean Nain craton from their reworked equivalents in the Paleoproterozoic Kaipokok domain of the Makkovik Province. In its early stages, the KNSZ bounded the Kaipokok domain as it was thermally softened by 1895-1870 Ma Andean-type magmatism, accompanied by dextral oblique convergence and resultant penetrative deformation. The amphibolite-facies tectonite that developed in this stage was widely overprinted by greenschist-facies mylonite. Laserprobe and spectral 40 Ar/ 39 Ar ages of recrystallized and porphyroclastic muscovite, from the greenschist-facies mylonite and from muscovite in a syntectonic quartz vein, bracket the age of deformation between 1740 and 1710 Ma with the best estimate at 1715 Ma. These ages are similar to those of A-type granites within the Makkovik Province and amphibole cooling ages from the province interior. Together with the petrological similarity of the greenschist-facies mylonite to localized low-grade shear zones elsewhere in the Makkovik Province, they are suggestive of a widespread, lithosphere-scale event. The 40 Ar/ 39 Ar data do not provide good constraints on the early activity of the KNSZ. However, preservation of relationships between granitoid sheets correlated with the 1895-1870 Ma Island Harbour Bay plutonic suite and early fabrics imply that the granites were emplaced syntectonically in the KNSZ. Thus, the KNSZ was a major, long-lived structure in the Makkovik Province that decoupled events in the reactivated Nain craton from an inert cratonic region.

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