BETWEEN THE SUPERCONTINENTS: MESOPROTEROZOIC DEER TRAIL GROUP, AN INTERMEDIATE AGE UNIT BETWEEN THE MESOPROTEROZOIC BELT-PURCELL SUPERGROUP AND THE NEOPROTEROZOIC WINDERMERE SUPERGROUP IN NORTHEASTERN WASHINGTON, USA

Mesoproterozoic and Neoproterozoic basins in western North America record the evolving position of the Laurentian craton within two supercontinents during their growth and dismemberment: Columbia (Nuna) and Rodinia. The westernmost Columbia rift-related Belt-Purcell Supergroup is preserved in NE Washington, where it is overthrust from the west by undated Deer Trail Group and its depositionally overlying Neoproterozoic Windermere Supergroup. It has been disputed whether the Deer Trail Group is correlative with the Belt-Purcell Supergroup or is younger. We characterize the detrital zircon (DZ) age populations of units from Deer Trail Group, Windermere Supergroup, and westernmost Belt-Purcell Supergroup to clarify the uncertain correlation of these units and their bearing on supercontinent evolution.

Our data show that the western part of the Columbia supercontinent (Mawson Continent of Australia-east Antarctica) continued to supply 1.6–1.5 Ga DZ grains to the westernmost Belt-Purcell Supergroup until after 1.39 Ga. The Deer Trail Group, characterized by muddy and dolomitic strata, begins with a basal distal turbidite unit younger than 1.36 Ga, grading up into a stromatolitic unit younger than 1.30 Ga. Deer Trail samples lack 1.6-1.5 Ga DZ and have a pre-Grenville-age provenance dominantly from the Yavapai and Mazatzal provinces of SW USA, with lesser input from Trans-Hudson and Archean sources to the east. Brennan et al. (Annual GSA 2019) used DZ Hf isotopes from basal Deer Trail to suggest its source also included eastern Antarctica, presumably still attached to SW USA until after 1.36 Ga. A flood of quartzose sand and conglomeratic debris begins with the overlying Buffalo Hump Formation. Previously considered part of the Deer Trail Group, it is clearly younger, with Grenville-age (ca. 1.1 Ga) DZ grains and a DZ signature like strata in the overlying late Neoproterozoic Windermere Rodinian rift basins. Windermere includes asthenosphere-sourced continent rift basalts, previously dated at 0.76 Ga, and glacial deposits. Windermere provenance includes Yavapai-Mazatzal sources, as well as a significant Trans-Hudson (1.85 Ga) DZ peak. We interpret that Deer Trail Group was deposited during rift-demise of supercontinent Columbia and before Grenville-age assembly of the supercontinent Rodinia.