SWEATING IT OUT IN ANTARCTICA, WITH ALL DUE RESPECT TO ELDRIDGE MOORES

The SWEAT hypothesis has been extremely stimulating to geological research in Antarctica. It was generally agreed that the late Precambrian-early Paleozoic Ross orogen, exposed throughout the Transantarctic Mountains, had developed along the passive margin of East Antarctica, but prior to SWEAT geologists did not speculate (at least in print) about the rifted nature of this margin, or what other continent might have been juxtaposed prior to separation. Unfortunately, unambiguous tests for the hypothesis are lacking within the confines of the Transantarctic Mountains. Aligning the boundaries between Mazatzal and Grenville rocks in west Texas and between 1.8-1.6 Ga and 1.0 Ga rocks in East Antarctica was suggested as a possible piercing point for Laurentia and Antarctica. But the boundary in Antarctica has been shown to be a Pan African suture between East and West Gondwanaland. As the years have gone by, the notion of Gondwanaland juxtaposed to western Laurentia has held, but Gondwanaland has slipped farther and farther “south” with the incursion of Siberia onto western Canada, and with the AUSWUS and AUSMEX reconstructions, leaving Antarctica to dangle without any certain continental mass joined to it.

In recent years additions and refinements have been made to the long-held, general model of the development of the Ross orogen. It is now recognized that a major discontinuity in the trends of the orogen occurs at Byrd Glacier. To the north in Victoria Land, mounting evidence suggests all of the metasedimentary and metavolcanic sequences are Neoproterozoic, while to the south from the central Transantarctic Mtns to the Pensacola Mtns the majority of the sequences are Early-Middle Cambrian. Detrital zircon data from this region have shown that much of the sedimentation previously assigned to Neoproterozoic is Cambrian. A model to be developed is that of a ribbon continent, >1,000 km long, colliding with the Antarctic margin to the south of Byrd Glacier in the latest Neoproterozoic-early Early Cambrian. New detrital zircon data from Victoria Land show a spike at 2.2-2.3 Ga. The one location along the west side of Laurentia where such a provenance is found is the Peace River arch in B. C. Alternatively, rocks of this interval are widespread throughout South America and Africa, suggesting counterparts to a dangling Antarctica.