Delineating the lithospheric architecture of the Rae cratons using Hf and O isotopes and trace elements in zircon

Characterizing the internal lithospheric architecture of Archean cratons is key to establishing the large-scale tectonic controls that contributed to their nucleation and formation and may play an important role in identifying the occurrence and distribution of mineral deposits. As many Archean cratons have experienced a polygenetic history, including multiple magmatic, metamorphic, and/or hydrothermal events, the primary architecture of cratonic crust may be reworked and obscured. The Rae craton in northern Canada, is no exception in that it grew through the accretion of Neoarchean (dominantly 2.58-2.75 Ga) crustal blocks followed by its amalgamation with the Slave, Hearne, and Superior cratons during <2.0 Ga Palaeoproterozoic orogenic events.

Hafnium (Hf) and oxygen (O) isotopic analysis of zircon in crustal rocks has proven to be a powerful tool to elucidate crustal architecture by identifying spatial and/or temporal changes in isotopic composition that directly relate to distinct crustal age and compositional domains within a craton. Specifically, Hf isotopic data addresses the age (and compositions) of the source to igneous rocks, including degree of contamination of juvenile magmatism, while O isotope compositions monitor the extent of recycling of hydrothermally altered or weathered crust. However, systematic Hf and O isotopic data for different bedrock source terranes within Archean terranes of northern Canada is not widely available limiting the ability to refine lithospheric structures that may be preserved in the crustal column.

In this study, we present preliminary in-situ U-Pb-Hf-O-trace element data from 115 Archean samples from across the Rae craton that were selected from the geochronology archive at the Geological Survey of Canada. All samples have been previously dated and were selected to cover the full spatial and temporal breadth of the craton with priority given to those preserving the highest quality zircon with the most unimodal age distributions. A small number of grains per sample were first dated by secondary ion mass spectrometry (SIMS) to confirm prior age determinations and to identify key grains for subsequent O and Hf isotope/trace element analysis by SIMS and laser ablation – inductively coupled plasma mass spectrometry, respectively. Collectively, these data will help refine petrological models of Rae crust formation, differentiate crustal domains that may or may not have experienced contrasting processes of formation, and contribute to identifying potential boundaries between isotopically different crustal blocks representing cryptic tectonic transitions within the cratons.