Magnetic fabric in mid-Cambrian rocks of the Central Flinders Zone and implications for the regional tectonic history

Magnetic fabric in the mid-Cambrian sedimentary rocks in the Central Flinders Zone, South Australia, varies from a bedding-parallel foliation to a well-developed lineation. No cleavage is visible in sampled outcrops but an incipient disjunctive cleavage is developed elsewhere. Comparison of magnetic-fabric data from different positions on a soft-sediment fold suggests that the magnetic lineation is not of depositional origin. Rather, it is interpreted as the result of two interfering generations of magnetic fabric: one is a compactional bedding-parallel magnetic foliation, and the other is a magnetic foliation of tectonic origin, defined by the girdle distribution of the site-mean lineation directions. This interpretation suggests that after bedding rotation during formation of the regional NNW-trending folds in the Central Flinders Zone, there was a phase of NNW-SSE-directed tectonic shortening during the Delamerian Orogeny. A model involving a southward-progressing orogeny could possibly account for the two phases of tectonic shortening, as well as for the development of the Nackara Arc in the Adelaide Fold Belt.