Grenville-age magmatism at the south Tasman Rise (Australia): a new piercing point for the reconstruction of Rodinia.

A U-Pb zircon sensitive high-resolution ion microprobe age of 1119.4 ± 8.5 Ma, obained 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).