Provenance of the Proterozoic Thelon Basin, Nunavut, Canada, from detrital zircon geochronology and detrital quartz oxygen isotopes

Abstract

The Paleoproterozoic Thelon Basin in Nunavat, Canada, is one of several large quartz-dominated sedimentary basins developed on Paleoproterozoic and Archean rocks of the Canadian Shield. Coarse-grained quartz to sub-feldspathic sandstones and conglomerates of the Thelon Formation comprise the basin fill. Detrital zircons from the Thelon Formation have LAM-ICP-MS 207Pb–206Pb ages ranging from 3.94 to 1.78 Ga, but most are Neoarchean (2.70–2.50 Ga). The δ18O values of quartz range from 7.7 to 13.9‰, and are typically 10–12‰. Ages, U/Zr ratios, and oxygen isotopic compositions of detrital quartz are consistent with a predominantly Neoarchean metasedimentary source, such as surrounds the eastern Thelon Basin and comprises the bulk of basement rocks within the Rae domain. The three stratigraphic sequences of the Thelon Formation have δ18O ranges for detrital quartz and zircon ages that further constrain the source areas and support previous sequence-stratigraphic interpretations. The lower sequence contains reworked siltstone and sandstone clasts and 2.50–1.85 Ga zircons indicating a contribution from Paleoproterozoic terranes. Detrital quartz δ18O values range from 9.8 to 13.9‰, indicating a metamorphic source also, which is consistent with a proximal source for the lower sequence. The middle sequence contains zircons exhibiting the widest range of ages (3.94–1.78 Ga). A >3.4 Ga Paleoarchean zircon population, cannot be correlated to the immediately surrounding basement and therefore indicates a distal source, possibly in the order of 1000–2000 km away. The upper sequence contains relatively few zircons due to extensive alteration but ages are predominantly early Paleoproterozoic and Neoarchean. The upper sequence strata contain the lowest δ18O values of quartz, indicating an influx of granitic material late in the depositional history of the basin. The geochronology and geochemistry of detrital grains within the Thelon Formation indicate that the source areas evolved from predominantly proximal to distal, and back to proximal as the basin filled.