Rodinian devil in disguise: correlation of 1.25—1.15 Ga strata between Tasmania and Grand Canyon, Arizona

Paleogeographic reconstructions of Rodinia typically place Australia or East Antarctica adjacent to the southwestern margin of Laurentia. Of critical importance to these reconstructions is a linkage of the 1.30—1.00 Ga Grenville orogen in southern Laurentia to Late Mesoproterozoic orogens in Australia or East Antarctica. The Grenville Orogeny in southern Laurentia was associated with an extensive episode of syn-orogenic sedimentation throughout the continental interior of southwest Laurentia, which is preserved as a series of isolated foreland basin exposures extending from present-day Texas through to New Mexico and Arizona and into California (Fig. 1). Like the hinterland of the Grenville orogen, this syn-orogenic basin system is truncated by the Neoproterozoic rift margin of Laurentia and may extend into the continent(s) to the west of Laurentia within Rodinia. This contribution explores the correlation of syn-orogenic basins in southwest Laurentia and Late Mesoproterozoic strata in Tasmania (southeast Australia). We present new field observations and detrital zircon U-Pb age and Hf isotopic data from the most complete exposures of the Late Mesoproterozoic syn-orogenic basin system of southwest Laurentia represented by the Unkar Group (Grand Canyon, Arizona) and from Late Mesoproterozoic strata comprising the upper Rocky Cape Group in Tasmania. The age and stratigraphy of the Unkar and upper Rocky Cape Groups show striking similarities with both successions comprising a lower package of ca. 1.25 Ga dolomite and shale, which is disconformably overlain by an upper succession of ca. 1.15 Ga quartz arenite (Fig. 1). We suggest the upper Rocky Cape Group is a correlate of the Unkar Group and represents a remnant of the extensive foreland basin system of the Grenville orogen in southern Laurentia, which supports the interpretation that Tasmania was located along the southwest margin of Laurentia in the Late Mesoproterozoic. Detrital zircon U-Pb age and Hf isotopic data indicate that both the Unkar Group and upper Rocky Cape Group were derived mainly from 1.80—1.40 Ga crust similar in character to basement terranes in southwest Laurentia. The Unkar and upper Rocky Cape Groups also contain abundant ca. 1.20 Ga detrital zircons with ɛHfi values between +10 and +2, consistent with a Late Mesoproterozoic source in the Grenville orogen of southern Laurentia characterized by a mixture of juvenile material and reworked southwest Laurentian Paleo—Mesoproterozoic basement. However, the ca. 1.15 Ga westerly-derived upper parts of the upper Rocky Cape Group also contain ca. 1.20 Ga detrital zircons with evolved Hf isotopic compositions (ɛHfi = -2 to -6), which are not observed in the Unkar Group dataset. Comparison of the upper Rocky Cape Group detrital zircon dataset with detrital zircon U-Pb-Hf isotopic data compiled from Late Mesoproterozoic orogens in Australia, East Antarctica, and South China indicate that Late Mesoproterozoic crust concealed beneath ice cover in the central Transantarctic Mountains of East Antarctica is the most suitable source for the westerly-derived parts of the upper Rocky Cape Group. A Late Mesoproterozoic position for Tasmania along the southwest margin of Laurentia and an East Antarctic provenance for the upper parts of the upper Rocky Cape Group support a connection between southwest Laurentia and East Antarctica within Rodinia at ca. 1.15 Ga.