Tuesday, 28 August 2007 - 10:30 AM
2.A.C-2
The Ross Orogen and Lachlan Fold Belt in Marie Byrd Land and New Zealand: implication for the tectonic setting of the Lachlan Fold Belt in Antarctica
John D. Bradshaw, Geological Sciences, University of Canterbury, 20 Kirkwood Avenue, Christchurch, New Zealand
Correlation of the Cambrian Delamerian Orogen of Australia and Ross Orogen of the Transantarctic Mountains is accepted but the extension of the adjacent Lachlan Orogen into Antarctica is controversial. Outside the main Ross-Delamerian belt, evidence of this orogeny is also preserved at Mt Murphy in Marie Byrd Land and the in Takaka Terrane of New Zealand. In pre-break configurations of the SW Pacific, these two areas are far removed from the Ross-Delamerian belt. Evidence from Cambrian conglomerates in the Takaka Terrane, however, shows that in Late Cambrian times it was adjacent to the Ross Orogen. These data indicate tectonic displacements within Gondwana after the Cambrian and before Gondwana break-up. The Lachlan Orogen formed in an extensional basin in a supra-subduction zone setting and the Cambrian rocks of Marie Byrd Land and New Zealand are interpreted as parts of a rifted continental ribbon on the outboard side of the Lachlan belt.