A U-Pb zircon sensitive high-resolution ion microprobe age of 1119.4 ± 8.5 Ma, obtained from a quartz syenite dredged from the South Tasman Rise (Australia), provides the first direct evidence of the presence of Grenville-age magmatic rocks along the central part of the hypothesized Australia–East Antarctica conjugate margin of Laurentia. The distinctive mineralogy and geochemistry of the rock and its Sm-Nd and Pb isotopic signatures 1) indicate that it represents a juvenile Grenville-age addition to the crust, 2) support a correlation with the Grenville magmatic province of the western United States, and 3) set a unique pivotal point for a precise reconstruction of Rodinia. The resulting scenario implies the presence of a new magmatic province crossing the East Antarctic craton, the extension of Proterozoic belts of southwest Laurentia to East Antarctica, and appears consistent with the Australia–western United States (AUSWUS) model. This tectonic setting envisages a near-local source for the ubiquitous Grenville-age detrital zircon population in marginal Neoproterozoic to early Paleozoic Gondwanan sequences and suggests a possible direct source for the widespread Grenville-age inherited zircon component observed in most Paleozoic granites in northern Victoria Land (Antarctica) and east Tasmania (Australia).

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