Geophysical testing of balanced cross-sections of fold–thrust belts with potential field data: an example from the Fleurieu Arc of the Delamerian Orogen, South Australia

Abstract

The Delamerian (South Australia) and Ross (Antarctica) Orogens once formed a continuous chain along the paleo-Pacific margin of Gondwana. Correlations between the two are based on many characteristics, including style of shortening and deformation. Constraining structural features in one of these orogens impacts on interpretations of tectonic processes for the other. Balanced cross-sections have provided crucial information on the internal architecture of the Delamerian Orogen, South Australia, and form a key piece of evidence in some widely circulated models for the deformational style. These sections have not been constrained by geophysical investigations, which can provide significant information about the subsurface geometry. We present magnetic forward models for two balanced cross-sections of the Fleurieu Arc in the Delamerian Orogen. The forward models require a larger volume of magnetic basement at shallower depths than predicted by balanced sections, requiring a revision of currently proposed shortening mechanisms. The shortening mechanism inferred from the models requires less imbrication of upper crustal units, and more folding above thrusts that involve both basement and cover sequences. This style of shortening compares favorably with published observations from the Ross Orogen in Antarctica.