Origin of the Archean Sask craton and its extent within the Trans-Hudson orogen: evidence from Pb and Nd isotopic compositions of basement rocks and post-orogenic intrusions

Abstract

U–Pb zircon ages from the exposed Sask craton are 2450–3100 Ma, from the Peter Lake Domain 2575–2640 Ma, and from rocks of the Trans-Hudson orogen 1840–1880 Ma. U–Pb monazite and zircon ages of post-orogenic pegmatites and aplites are 1770–1800 Ma. Common Pb and Sm–Nd isotopic compositions of post-orogenic intrusions, as probes of crust beneath the orogen, were compared to Sask craton rocks and ca. 1850 Ma orogenic rocks to infer the origin and subsurface distribution of the Sask craton within the internides of the Trans-Hudson orogen. Results show that post-orogenic intrusions within most of the Glennie Domain and Hanson Lake block were derived, at least in part, from Archean source materials, demonstrating that the Sask craton lies beneath Paleoproterozoic orogenic rocks present at the surface. In contrast, common Pb and Sm–Nd isotopic compositions from pegmatites and aplites of the La Ronge Domain are essentially identical with those of the Paleoproterozoic orogenic rocks into which they are intruded, indicating derivation by partial melting of similar rocks. Thus, if the Sask craton extended to the west beneath the La Ronge Domain, it was beneath the zone of melting that produced the post-orogenic intrusions, making it unlikely that the Sask craton is a detached part of the Hearne craton. Many samples from the Sask craton have elevated 208Pb/204Pb ratios, unlike Superior craton or Hearne craton rocks, suggesting that the Sask craton was derived from an exotic source, such as the Wyoming craton, which shares similar elevated 208Pb/204Pb ratios.