A Contiguous Taltson‐Thelon Margin Revisited.

The amalgamation of Laurentia was initiated along the western margin of the Rae craton. However, the tectonic setting that generated magmatic rocks along this margin has long been debated, with the Thelon tectonic zone in the north having formed in an arc setting, and the Taltson magmatic zone in the south variably attributed to either continental arc or intracratonic magmatism. The magmatic rocks of the Great Slave Lake shear zone (GSLsz) lie between these two tectonic belts and, thus, may be critical to the interpretation of the evolution of the western Rae margin. To understand the origin of the rocks in the GSLsz, we have applied U‐Pb geochronology, trace‐element geochemistry, and O and Hf isotope analyses to zircons from a suite of samples that transect the La Loche River fault (LRf)—a major structure that bisects the GSLsz. Samples collected to the north of the LRf are Neoarchean in age, have mantle‐like δ18O (4.7–5.8‰) and chondritic to juvenile εHf values (0–4.5), whereas those to the south are exclusively Paleoproterozoic in age and have more elevated δ18O (6.3–7‰) and much more evolved εHf values (−12 to −6); these results indicate that the LRf marks a crustal‐scale suture between the Slave craton and the Taltson magmatic zone. Our isotopic data, together with other regional constraints from the area, are most consistent with the Taltson magmatic zone having formed in a continental arc setting emplaced into ca. 2.3 Ga juvenile basement crust. Plain Language Summary: The amalgamation of the Canadian Shield was initiated along the western margin of the Rae craton, one of the principal Archean landmasses. The rocks along the Great Slave Lake shear zone (GSLsz) are situated between the Thelon tectonic zone in the north and the Taltson magmatic zone in the south, two magmatic belts with debated tectonic histories. We use U‐Pb geochronology and oxygen and hafnium isotopes in zircon to understand the origin of rocks along GSLsz. To the north of the La Loche fault, one of the main structures within the GSLsz, rocks are Neoarchean in age with oxygen and hafnium isotopic values similar to that of the Slave craton, while those to the south are exclusively Paleoproterozoic in age with similarities to the Taltson magmatic zone. The La Loche River fault, thus, marks a significant boundary between the Slave craton and the Taltson magmatic zone. The isotope results also suggest that the Taltson magmatic zone formed in an arc setting, providing refinement to the tectonic model invoked for the formation of the Canadian Shield. Key Points: U‐Pb ages together with oxygen and hafnium isotopes are effective at characterizing the contrasting geology across major structuresThe La Loche River Fault is a crustal‐scale structure separating the Slave craton from the Taltson magmatic zoneThe geochronology and isotopic data presented herein are most consistent with the Taltson magmatic zone having formed in an arc setting [ABSTRACT FROM AUTHOR]