Age and provenance of the Paleoproterozoic Thluicho Lake Group based on detrital zircon U–Pb SHRIMP geochronology: new insights into the protracted tectonic evolution of the southwestern Rae Province, Canadian Shield

The middle Paleoproterozoic Thluicho Lake Group comprises coarse-grained continental clastic rocks deposited in fault-controlled alluvial basin(s) in the southwestern Rae Province of the Canadian Shield. The group nonconformably overlies crystalline basement that records late-Taltson high-grade metamorphism, ca. 1.93 Ga, and is folded and metamorphosed to greenschist facies, providing an important window of insight into tectonic activity in this region. This paper reports ∼100 detrital zircon ages for two samples from the lower and upper parts of the Thuicho Lake Group. Four analyses of one of the youngest detrital zircons from the stratigraphically higher member define a weighted mean 207Pb/206Pb age of 1922 ± 6 Ma, establishing a maximum depositional age for the group. This result accords with regional geological relationships indicating that the group is intermediate in age between development of two major tectonic fronts; an older, ca. 1.93 Ga east-southeast-trending front that formed at the height of Thelon-Taltson orogeny, and a younger, ca. 1.91–1.90 Ga northeast-striking front expressed by the Black Bay Fault and related northeast-striking structures affiliated with the Snowbird tectonic zone. The younger age limit of the group may therefore be older (≥1.91–1.90 Ga) than the previously reported minimum age, constrained by cross-cutting dykes dated at ca. 1.82 Ga. In terms of isotopic provenance, the bulk of analyses of the combined dataset lie within two principal age-ranges: 2750–2500 Ma and 2475–2250 Ma. The older of these is dominated by ca. 2600 Ma zircons, whereas the younger contains two statistically distinct subgroups of 2410 and 2310 Ma. This signature is consistent with derivation almost exclusively from immediately surrounding basement rocks of the Nolan, Taltson, Zemlak, Ena and Beaverlodge domains. Abundant 2475–2250 Ma zircons provide indirect evidence for the 2.45–2.3 Ga Arrowsmith orogeny. Despite proximity to the Taltson magmatic zone, 1990–1960 Ma zircons are nearly completely absent, suggesting that Thluicho Lake basins formed in the hinterland of the orogen, possibly separated from the foreland (Taltson arc) by a continental divide. Alternatively, Taltson arc plutons may not have been unroofed at the time of deposition of Thluicho Lake strata. The data presented herein support the previously proposed broad correlation between the Thuicho Lake and Nonacho groups; however, there are apparent differences in detail between respective basin settings and controls, suggesting that this correlation requires further investigation.