EXOTIC PROVENANCE FOR THE PROTEROZOIC HESS CANYON GROUP, ARIZONA, USA: IMPLICATIONS FOR BASIN EVOLUTION AND CA. 1.4 GA CONTINENT CONFIGURATIONS

Detrital zircon data from the upper parts of the Proterozoic Hess Canyon Group of southern Arizona reveal abundant 1600-1490 Ma detrital zircons, ages essentially unknown from southern Laurentia. This basinal succession may be up to 3000 m thick and is underlain by more than 2000 m of rhyolite of the Redmond Formation. Ca. 1660 Ma rhyolite of the upper Redmond Formation is intercalated with the lower part of the overlying White Ledges Formation, thus establishing the maximum age of Hess Canyon Group deposition. The 300-m-thick White Ledges Formation contains abundant orthoquartzite with predominately unimodal detrital zircon age probability distributions and peak ages at 1778­–1726 Ma. The argillaceous Yankee Joe and quartzite-rich Blackjack Formations show a pronounced shift toward younger detrital zircon with peak ages ranging from 1666 to 1494 Ma. Ca. 1494 Ma represents a new maximum depositional age for the two units, and prominent age peaks at 1582, 1567, and 1515, 1495, and 1494 Ma in three samples represent zircon ages that are either uncommon or entirely absent in Laurentia. The Blackjack Formation is cut by the ca. 1450 Ma Ruin granite, indicating that deposition and deformation occurred between 1494 and 1450 Ma. This age range generally predates a widely recognized episode of intracontinental tectonism in southwestern Laurentia between ca. 1440 and 1360 Ma. Our findings reveal a potential ca. 170 m.y. discontinuity within the Hess Canyon Group and provide a new record of Early Mesoproterozoic sedimentation and tectonism in southern Arizona. This new record helps to fill a well documented 1.60–1.45 Ga tectonic gap in southern Laurentia and supports hypotheses for a long-lived Proterozoic tectonic margin along southern Laurentia ca. 1.8–1.0 Ga. Ca. 1.6–1.5 Ga detrital zircon ages in the Yankee Joe and Blackjack Formations establish these two units as potential piercing points for Nuna reconstructions as the ages favor Australia but also permit Amazonia as an outboard source for the exotic detritus ca. 1.49–1.45 Ga.