SUPERCONTINENT RECONSTRUCTION FROM ACCRETIONARY HISTORY AT LEADING CONTINENTAL EDGES

Repeated amalgamation and subsequent break-up of continental lithosphere have profoundly affected Earth's evolution since the Archean. Distinctive rift-related stratigraphy and magmatism followed by passive margin development along the trailing edges of dispersing continents have been used to identify such margins in the geologic past. Using the isotopic record of Mesozoic-Cenozoic igneous rocks of western North America as an analogue, we show that the leading edges of dispersing continents have Sm-Nd isotopic characteristics that may be used to identify these margins in the geologic past. The Sm-Nd isotopic signatures of Late Neoproterozoic and Early Paleozoic igneous rocks along the northern Gondwanan margin indicate derivation from 0.7 to 1.1 Ga mantle lithosphere. This lithosphere originated in the Mirovoi Ocean that surrounded Rodinia, accreted to the northern Gondwanan margin by ca. 650 Ma in response to Rodinia breakup, and provided a source for subsequent magmatism. The accretion and subsequent recycling of oceanic mantle lithosphere should be common along the leading edges of dispersing continents following supercontinent breakup. Identification of this phenomenon should therefore provide an additional aid in paleocontinental reconstructions.