Two Distinct Ages of Neoarchean Turbidites in the Western Slave Craton: Further Evidence and Implications for a Possible Back-Arc Model

The supracrustal assemblages of many Archean cratons contain significant volumes of graywacke-mudstone turbidites, and, notably, the stratigraphy of the Slave craton is dominated by these rocks (similar to 70%). Phanerozoic sedimentary successions are used extensively in deciphering the evolution of an orogen, but, in contrast, Archean turbidites have not added as significantly to our understanding of the tectonic evolution of Archean cratons. This is because geological complexities, such as a lack of fossils and marker units, leave regional correlations ambiguous and tectonic models provisional. We use the U-Pb SHRIMP isotopic analyses of detrital zircons to investigate the maximum deposition ages of graywacke-mudstone turbidites from five locations in the western Slave craton and develop regional correlations. Our results, when tied with those of previous studies, indicate that the extensive turbidites can be separated into at least two packages. Package I turbidites generally lack interbedded iron formation and were deposited at ca. 2660 Ma. Previous studies indicate deposition in a rifting arc, a setting consistent with our results. Package II contains extensive interbedded iron formation and was deposited between 2640 and 2610 Ma. We establish, for the first time, that package II turbidites were deposited on the older stratigraphy of the craton, including Mesoarchean basement. The results suggest a spatial and temporal relationship between the package II turbidites and the northeast-trending ca. 2635-2620-Ma Defeat magmatic arc. We couple these relationships with regional geologic constraints and interpret that package II turbidites were deposited before collision in a continental back-arc setting between 2630 and 2610 Ma. Our results further highlight the utility of U-Pb dating of detrital zircons in Archean sedimentary sequences.