Episodic Paleoproterozoic crustal growth preserved in the Aillik Domain, Makkovik Province, Labrador

Abstract

The convergent margin of southeastern Laurentia consists of reworked continental crust as well as accretion of continental ribbons and juvenile arc terranes forming part of the Great Proterozoic Accretionary Orogen. The Makkovik orogen, in Labrador, preserves evidence of the timing, duration and complexities of these accretionary events during the interval 1.88–1.78 Ma.New regional bedrock geological mapping combined with new U-Pb zircon SHRIMP ages constrain the Paleoproterozoic felsic magmatism in the Aillik Group of the Makkovik orogen. Nine samples from the Aillik Group yield magmatic 207Pb/206Pb ages between 1883 ± 7 Ma and 1858 ± 3 Ma. The ages extend the previously documented ages of felsic volcanism, providing evidence for periodic volcanism spanning 35 m.y. with the most prolific volcanic activity occurring ca. 1860 Ma. Combined with previous studies, the Aillik Group is now constrained between 1883 ± 7 and 1848 ± 2.7 Ma. Development of a pervasive planar fabric associated with the northwestward thrusting of the Aillik Group (D3) occurred after 1848 Ma.Lithotectonic evolution in the Makkovik Province comprised significant crustal reworking, magmatism, and minor preserved juvenile crustal growth between ca. 1883 and 1848 Ma. The revised model for formation of the Aillik Group proposed herein suggests that the Aillik Group formed in a continental back-arc setting. These new ages further refine the timing of the accretionary events as well as characterizing the age of the crustal root of the arc, which could be a juvenile substrate (Neoarchean/Paleoproterozoic) or reworked Archean crust, possibly the 2.3–2.6 Ma Mistinibi-Raude crust of the Southeast Churchill Province.