| Summary: | A major challenge facing paleogeographic reconstructions of the Late Mesoproterozoic supercontinent Rodinia isidentifying the extension of the Grenville orogen in continents formerly adjacent to western Laurentia (ProterozoicNorth America). Many paleogeographic reconstructions of Rodinia link exposures of the Grenville orogen insouthern Laurentia to Late Mesoproterozoic orogens in central Australia or in the Transantarctic Mountains of EastAntarctica. The Grenville Orogeny in southern Laurentia was accompanied by regionally extensive sedimentationin the interior of the continent, represented by a series of Late Mesoproterozoic basins throughout southwestLaurentia. The Late Mesoproterozoic basin system of southwest Laurentia is truncated by the Neoproterozoicrifted margin of western Laurentia produced during the breakup of Rodinia. Remnants of this basin system couldbe exposed on continents formerly adjacent to western Laurentia and may therefore be an important piercingpoint for refining paleogeographic reconstructions of Rodinia. In this contribution, we identify a possiblefragment of the Late Mesoproterozoic basin system of southwest Laurentia represented by the upper Rocky CapeGroup of western Tasmania, Australia. We test the correlation between Late Mesoproterozoic strata in southwestLaurentia and western Tasmania through new field observations and detrital zircon U-Pb-Hf isotopic data fromexposures of the Unkar Group (Grand Canyon, Arizona) and the upper Rocky Cape Group. The stratigraphy of the Unkar Group and upper Rocky Cape Group are remarkably similar with both successionscomprising a lower subdivision of stromatolitic dolomite and siltstone overlain by quartz arenite withsoft-sediment deformation features. Detrital zircons age distributions from the Unkar and upper Rocky CapeGroups are both characterized by large age peaks at 16001800 Ma, prominent 1450 Ma peaks, abundant14001300 Ma ages, and youngest peaks at ca. 1220 Ma. The 1450 Ma zircons from the Unkar Group haveinitial epsilon Hf values (Hfi) of 3.7612.95, comparable to Hfi values of 1.8412.53 from 1450 Ma zirconsfrom the upper Rocky Cape Group. The 14001300 Ma zircons from the Unkar Group have Hfi of 1.1611.89,which is similar to time-equivalent grains from the upper Rocky Cape Group (Hfi = 1.3312.47). The youngestzircons from the Unkar Group (13001200 Ma) have Hfi of -0.7812.74 Ma, which generally overlap with theHfi of 13001200 Ma zircons from the upper Rocky Cape Group, although the latter includes grains with Hfi aslow as -6.26. The age distribution and Hf isotopic composition of detrital zircons from the Unkar and upper Rocky CapeGroups are consistent with derivation from basement sources in southern Laurentia including the Grenvilleorogen. Correlation of the Unkar and upper Rocky Cape Groups is supported by similarities in stratigraphy anddetrital zircon provenance and suggests western Tasmania formed part of the Late Mesoproterozoic basin systemof southwest Laurentia. The close affinity of the Proterozoic geology of western Tasmania to the TransantarcticMountains of East Antarctica indicates that the new correlations presented here support the interpretation that theGrenville orogen extended into the Transantarctic Mountains, implying a connection between southwest Laurentiaand East Antarctica within Rodinia.
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