LONG-LIVED (1.8-1.0 GA) CONVERGENT OROGEN IN SOUTHERN LAURENTIA - EVALUATION OF THE AUSWUS MODEL FOR RODINIA

Our approach to Rodinia reconstructions is to evaluate time-integrated "piercing points" by understanding the tectonic evolution of orogenic systems rather than single events or belts. For the Australia- Laurentia connection, we evaluate the original Rodinia reconstruction (SWEAT), but support an alternate reconstruction (AUSWUS), and comment on a recent modification (AUSMEX). Between 1.8 and 1.0 Ga, a series of subparallel accretionary orogens were added progressively to the southern edge of Laurentia. These belts now extend along strike from Greenland/Labrador to southern California and are truncated at late Precambrian passive margins. We propose that Australia contains at least part of their western continuation. Together they comprise a long-lived orogenic system, >10,000 km long, that preserves a record of 800 million years of convergent margin tectonism. This tectonism culminated during Grenvillian continent-continent collisions in the assembly of the supercontinent Rodinia. The AUSWUS reconstruction places Australia adjacent to the southwestern U.S in the Paleo and Mesoproterozoic rather Antarctica. This reconstruction is supported by a distinctive "fingerprint" of geologic similarities between Australia and the southwestern U.S. from 1.8 to 1.0 Ga. There are still no unequivocal piercing points, however, and paleomagnetic data suggest that Australia was farther south at 1.1 Ga (AUSMEX) and had separated from Laurentia by 800 Ma. If these single pole positions are correct, East Gondwana may have moved in a transcurrent sense relative to Laurentia in the Mesoproterozoic, but without complete separation, and Siberia or South China may have been adjacent to western Canada. The proposed geologic association of Australia with Laurentia, and the proposed long-lived convergent margin, provide a set of testable implications for the tectonic evolution of these cratons. In addition to further supporting the general AUSWUS reconstruction, we suggest that there was a globally significant, contiguous orogenic system that extended from Australia, across southern Laurentia, to Baltica during the Paleo- and Mesoproterozoic, perhaps analogous in scale to the modern Cordillera. These belts then became variably overprinted by 1.1-1.0 Ga continent-continent collisions during the Grenville orogeny and were dismembered starting about 800 Ma.