Abstract

In Cambrian time, Laurentia was bounded on all sides by passive margins, providing an opportunity to establish a “Cambrian baseline” of detrital zircon provenance for the craton during a relatively quiescent tectonic stage. U-Pb detrital zircon ages from laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) and sensitive high-resolution ion microprobe (SHRIMP) analysis of seven Cambrian sandstone samples from northern Northwest Territories are consistent with generally local provenance. Samples from Mackenzie Mountains were most likely derived from the Proterozoic Mackenzie Mountains Supergroup and are dominated by detrital zircon ages of ca. 1020–1516 Ma, but also contain populations of ca. 1615–1692 Ma and ca. 2699–2752 Ma. Cambrian sandstones from south of Great Bear Lake have a complementary set of detrital zircon age populations dominated by ca. 1810–2010 Ma, with smaller relative probability peaks at 2100 Ma, 2300 Ma, and 2600 Ma, which are consistent with derivation from the Hottah terrane, Great Bear magmatic zone, and Slave craton. Comparison of the signatures from Mackenzie Mountains and Great Bear Lake south suggests that there were two distinct sources of detrital zircon available to the northern Northwest Territories during the Cambrian. Detrital zircon ages from Cambrian strata of Victoria Island appear to be a mixture of Shaler Supergroup, Slave craton–like, Taltson-Thelon orogen, and Wopmay orogen sources.

Following the dichotomy of detrital zircon age spectra presented by Cambrian samples from Mackenzie Mountains and Great Bear Lake south allows subdivision of other published detrital zircon ages from across northern Laurentia into two groups: Laurentia Cambrian type 1 suite reflects the Archean cratons and Paleoproterozoic orogens of the Precambrian Shield. Laurentia Cambrian type 2 suite is dominated by Grenvillian and older ages (1000–1500 Ma) and includes relative probability peaks at 1600–1700 Ma and 2700–2750 Ma. We find, therefore, that this Cambrian baseline mirrors the Precambrian tectonic fabric of Laurentia from Archean cratonization and Paleoproterozoic through Mesoproterozoic orogenesis, culminating in assembly of the supercontinent Rodinia. Furthermore, the Neoproterozoic breakup of Rodinia and establishment of passive margins surrounding Laurentia provided little new zircon available to the Cambrian sedimentary system. The detrital zircon spectra for the Cambrian of northern Laurentia are intended to provide a reference to test the affinity of suspect terranes and potentially exotic detrital zircon within Paleozoic foreland basins.

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