Lithogeochemical and Nd isotopic constraints on felsic magmatism in the Makkovik Orogen, Labrador, Canada: Implications for assembly of the supercontinent Nuna

Abstract

The formation of the supercontinent Nuna was a significant global crustal accretion event during the interval 1900 to 1800 Ma. Insight into its amalgamation is preserved in felsic volcanic of the Aillik Group and associated porphyritic intrusive rocks from the Makkovik Province. Lithogeochemical data indicate compositions typical of ferroan (A-type) felsic magmas. Trace-element ratios, such as high La/Yb(pm), are indicative of partial melting at high temperatures (~850–900 °C). Most samples have εNd(t) between +0.1 and −5.2, with T(DM) from 2773 to 2160 Ma, suggesting derivation through anatexis of predominantly Neoarchean to Paleoproterozoic sialic crust. One sample, however, has εNd(t =1860 Ma) = +3.0 and T(DM) of 1927 Ma, comparable with two other published values, indicative of a large component of juvenile asthenospheric material in its origin. This suggests that the felsic rocks may, alternatively, have been derived from a highly fractionated mantle melt with variable Neoarchean to Paleoproterozoic crustal contamination. It is likely that a mixture of both end-member models, anataxis and fractional crystallization, were active in the generation of these felsic magmas.The Aillik Group is genetically more closely related to the Cape Harrison arc than previously thought. It is, herein, proposed that there are likely only two domains (Kaipokok and Adlavik) preserved in the Makkovik Province. The Aillik Group was deposited in a backarc setting during the initial stage of the Cape Harrison arc, and was subsequently thrust over the Kaipokok arc. This thrusting resulted in the formation of crustal-scale shear zones that localized fluids and increased the metallogenic tenor of the region, consistent with the mode of formation of other accretionary belts of Nuna.