The metallogenic significance of juvenile crust formation during the assembly of the supercontinent Nuna: Lithogeochemical and isotopic evidence from felsic magmatism, Makkovik Province, Labrador, Canada.

Abstract:

The Makkovik Province of Labrador documents part of the amalgamation of the supercontinent Nuna; an event that records significant continental crustal growth over a relatively short period between 1900 and 1800 Ma. Insight into the amalgamation of Nuna is preserved in felsic volcanic rocks and associated hypabyssal intrusive rocks of the Aillik Group

Major- and trace-element signatures are indicative of compositions typical of A-type felsic volcanic rocks and granites. Trace-element patterns are typical of melts derived by partial melting of sialic crust, having strong negative Nb and Ti anomalies; signatures typically of crustal-derived melts related to either subduction or crustal-contamination processes. Trace-element ratios, such as high La/Yb_(PM) and Zr/Y, indicate a low degree of partial melting at high temperatures (~850 ‒ 900^oC). The felsic volcanic rocks and syn-volcanic intrusions have εNd₍₀₎ values that range from -3.0 to -5.2, with T_(DM) model ages that range from 2773 Ma to 1927 Ma, suggesting derivation by partial melting of predominantly NeoArchean to Paleoproterozoic crust.

The Aillik Group and plutonic equivalents formed in a back-arc setting, and the substrate of the arc was likely ca. 2600 to 2300 Ma cratonic material.

The Aillik Group was likely deposited proximal to the Cape Harrison Arc, and was subsequently thrust over the North Atlantic Craton after ca. 1836 Ma. This thrusting resulted in the formation of crustal-scale shear zones that localized fluids and increased the metallogenic tenor of the region, consistent with other accretionary belts in Nuna.