RECONSTRUCTING RODINIA: HAFNIUM RESULTS FROM THE SW LAURENTIAN “MAGMATIC GAP” (1470-1600 MA) POSSIBLE LINKS BETWEEN THE YANKEE JOE BASIN AND CENTRAL AUSTRALIA

Detrital zircons collected from the Yankee Joe and Blackjack Formations of the Hess Canyon Group of the upper Salt River Canyon in central Arizona reveal abundant 1600-1490 Ma detrital zircons, ages essentially unknown from southwestern Laurentia. Within the Hess Canyon Group, detrital zircon peak ages from the basal White Ledge Formation to the overlying Yankee Joe and Blackjack Formations define a 165 m.y. shift to younger zircon ages. This disconformity distinguishes a new depositional system and a previously unrecognized basin. The new Yankee Joe Basin contains detrital zircon peak ages of 1567 and 1610 Ma, with a subordinate peak at 1495 Ma – a new maximum depositional age. These ages fill a conspicuous “magmatic gap” for southwestern Laurentia (1600-1450 Ma). Therefore, the detritus is exotic and derived from sources not recognized in SW Laurentia. Between 1490 and 1436 Ma, the Yankee Joe and Blackjack Formations were folded by northwest directed compression. At 1436 Ma, the section was intruded by Ruin Granite, part of a widely recognized episode of 1.45-1.35 Ga intracontinental tectonism in SW Laurentia. This deformation is consistent with a long-lived convergent margin that persistently defined the southern margin of Laurentia and demonstrates a tectonic continuum from 1.8 – 1.0 Ga.

Hafnium analysis ran on the dated zircons of the Yankee Joe and Blackjack Formation show epsilon Hafnium values that range from +2 to +17, overlapping the depleted mantle evolution curve and is indicative of juvenile primary sources. When compared to continental distributions compiled by Belousova and others (2010), the epsilon Hafnium plots from the Yankee Joe and Blackjack Formations are consistent with abundant 1650-1450 Ma juvenile sources documented in central Australia. We propose that these new detrital zircon ages and epsilon Hafnium values offer important new piercing points for 1.5 Ga Nuna reconstructions, critical to understanding the evolution of Rodinia.