Acasta Gneiss

[9] The Acasta Gneiss Complex is a heterogeneous assemblage of foliated to gneissic tonalites, trondhjemites, granodiorites, and granites which contains minor quartz-diorites, diorites, gabbros, and ultramafic rocks.

The base of younger Late Mesoarchean greenstone belts that comprise the Central Slave Cover Group consists largely of fuchsite-bearing quartz arenite,.

Finally, these rocks were intruded by multiple Paleoproterozoic dike swarms and syenites about 1.80 Ga.[15] The setting in which the tectonic activity that created the Acasta Gneiss Complex is proposed to have been a block of dominatly mafic protocrust, at least some of which crystallized in the Hadean.

[1][3] With zircon U-Pb crystallization ages as old as about 4.03 Ga, beds within the Acasta Gneiss Complex are, as of 2019[update], regarded to be the oldest known felsic rocks (crust) on Earth.

Unfortunately, because of the basaltic composition and low-Zr content of the rocks comprising Nuvvuagittuq Greenstone Belt, they essentially lack the igneous zircons needed to reliably date them.

U-Pb crystallization ages of igneous zircons from felsic, trondhjemitic bands of intrusive origin within the Nuvvuagittuq Greenstone Belt only demonstrate that these rocks are older than 3.768 Ga.[16]