FORMATION AND EVOLUTION OF THE AILLIK DOMAIN, MAKKOVIK PROVINCE: A PALEOPROTEROZOIC ACCRETIONARY OROGEN PRESERVED IN LABRADOR, CANADA

The Makkovik Province of Labrador, Canada, is part of a Paleoproterozoic accretionary orogen that developed on the southern margin of the North Atlantic craton during the ca. 1.9–1.7 Ga Makkovikian-Ketilidian orogeny. The Aillik domain is one of three domains that characterize the Makkovik Province and is largely comprised of: a) the Aillik Group (previously termed the Upper Aillik Group), a supracrustal assemblage consisting of metasedimentary and metavolcanic rocks; and, b) abundant, syn- and post-deformation Paleoproterozoic intrusive suites which intrude the Aillik Group. The ca. 1883-1856 Ma Aillik Group comprises polydeformed, upper-greenschist to lower-amphibolite facies, bi-modal volcanic rocks and sedimentary lithologies and hosts abundant base-metal and uraniferous mineral occurences. Intrusive suites in the Aillik domain include: ca. 1858 Ma foliated syn-volcanic quartz–feldspar-porphyritic granites, ca. 1805–1795 Ma foliated to massive granitic intrusions, and non-foliated ca. 1720 Ma and Labradorian (ca. 1650–1640 Ma) granitic and gabbroic intrusions.

Deformation in the Aillik Group is predominantly characterized by regional-scale, open to isoclinal, moderately plunging, upright to overturned folds (F₁ in the Aillik domain) that were subsequently refolded (F₂). Folding and the development of regional-scale shear zones was contemporaneous with the formation of an axial-planar fabric in the Aillik Group and regional amphibolite-facies metamorphism, all of which are attributed to compressional tectonic regimes associated with the Makkovikian orogeny. With the exception of the porphyritic, syn-volcanic granites, all of the plutonic rocks appear to postdate regional-scale folding in the area. Although some of the ca. 1800 Ma plutons have acquired the regional penetrative fabric, indicating that they intruded synchronous to deformation, they do not appear to be folded.

Lithological characteristics of the Aillik Group support formation in a transitional environment, from a shallow marine to a marginal marine or subaqueous environment. Although depositional basement has not been identified, it cannot be coincident with present-day basement, as folding and shearing during Makkovikian orogenesis transported these Aillik Group rocks northwestward.