The Paleoproterozoic Kaminak dykes, Hearne craton, western Churchill Province, Nunavut, Canada: Preliminary constraints on their age and petrogenesis

Abstract

The NNW- to NNE-trending Kaminak diabase dykes, exposed in the Hearne craton of the western Churchill Province, Canada, are components of a Neoarchean–Paleoproterozoic LIP that forms an important pin in plate tectonic reconstructions impacting models for the assembly of the Nuna supercontinent. This study provides the first detailed information on the age, geochemistry and isotopic composition of these dykes.A precise U–Pb baddeleyite date of 2497.6±1.1Ma, obtained for one dyke sample, provides the best estimate for the timing of Kaminak mafic magmatism. The dykes are tholeiitic basalts to basaltic andesites with consistent compositions over an areal extent of ∼10,000km2. Major and compatible trace element variations indicate that the dykes were not in equilibrium with anhydrous peridotitic mantle and evolved through fractionation of Pl+Cpx±Ol from parental melts in the deep crust. All dykes record remarkably similar, incompatible element enriched, closely parallel multi-element profiles with variable HFSE troughs, comparable to Phanerozoic low-TiO2 continental tholeiites. Time-corrected Nd isotopic compositions overlap, or are slightly below bulk Earth (εNd2500 Ma=+0.4 to −0.8), and yield TDM values (2.75–2.87Ga) comparable to those of igneous crust in the Hearne craton. Implied short residence times, along with the geological, geochemical and isotopic data, are interpreted to imply that parental magmas of the dykes were low-TiO2 tholeiites generated via contamination of primary, depleted N-MORB-like magmas by low-degree, calc-alkaline lamprophyre melts in the continental lithospheric mantle. The melts homogenized in chambers near the Moho and underwent extensive fractional crystallization (Pl+Cpx±Ol), and possibly minor assimilation of lower crust, prior to injection into the upper crust. Paucity of evidence for contemporaneous lithospheric rifting, homogeneous lithogeochemical and Nd isotopic compositions, and petrochemical variations distinct from the Matachewan and Mistassini swarms of the Superior Province suggest the Kaminak dykes are the magmatic products of a Late Archean–Early Paleoproterozoic mantle thermal anomaly that extended, but did not break apart the Hearne craton. The results of this study do not support direct correlation of the Kaminak and Matachewan or Mistassini dyke swarms. Further evaluation of the proposed linkage of the Hearne and Superior cratons prior to Nuna supercontinent assembly requires additional geochronological, lithogeochemical and radiogenic isotopic constraints.