In the Cape Caribou River allochthon (CCRA), metaigneous and gneissic
units occur as a shallowly plunging synform in the hanging wall of the
Grand Lake thrust system (GLTS), a Grenvillian structure that forms the
boundary between the Mealy Mountains and Groswater Bay terranes. The
layered rocks of the CCRA are cut by a stockwork of monzonite dykes
related to the Dome Mountain suite and by metadiabase-amphibolite dykes
that probably form part of the ca. 1380 Ma Mealy swarm. The mafic dykes
appear to postdate much of the development of subhorizontal metamorphic
layering within the lower parts of the CCRA. The uppermost (least
metamorphosed) units of the CCRA, the North West River
anorthosite-metagabbro and the Dome Mountain monzonite suite, have been
dated at 1625 +/- 6 and 1626 +/- 2 Ma, respectively. An amphibolite unit
that concordantly underlies the anorthosite-metagabbro and is intruded
discordantly by monzonite dykes has given metamorphic ages of 1660 +/- 3
and 1631 +/- 2 Ma. Granitoid gneisses that form the lowest level of the
CCRA have given a migmatization age of 1622 +/- 6 Ma. The effects of
Grenvillian metamorphism become apparent in the lower levels of the
allochthon where gneisses, amphibolite, and mafic dykes have given new
generation zircon ages of 1008 +/- 2, 1012 +/- 3, and 1011 +/- 3 Ma,
respectively. A posttectonic pegmatite has also given zircon and
monazite ages of 1016(-3)(+7) and 1013 +/- 3 Ma, respectively. Although
these results indicate new growth of Grenvillian zircon, this process
was generally not accompanied by penetrative deformation or melting.
Thus, the formation of gneissic fabrics and the overall layered nature
of the lower CCRA are a result primarily of Labradorian (1660-1620 Ma)
tectonism and intrusion, and probably reflect early movement on an
ancestral GLTS. Grenvillian heating and metamorphism (up to granulite
facies) was strongly concentrated towards the base of the CCRA and
probably occurred during northwestward thrusting of the allochthon over
the Groswater Bay terrane.