Palaeoproterozoic regional-scale non-coaxial deformation: an example from eastern Eyre Peninsula, South Australia

Regional-scale high-grade structures preserved in an Archaean-Palaeoproterozoic gneissic belt, in eastern Eyre Peninsula, are attributed to the development of the Kalinjala Shear Zone. The Kalinjala Shear Zone is an similar to 200 km long high-grade dextral transpressional shear zone that formed during the similar to 1730-1700 Ma Kimban Orogeny (KD1 and KD2). The first deformation event, KD1, involved a large component of northeast-southwest sub-horizontal stretching (parallel to X) and formed abundant meso- to macro-scale sheath folds and a well-developed prolate > 10:1:1 (X > Y > Z) L-fabric (KL1; L much greater than S) during transitional granulite facies conditions. The second event, KD2, was dominated by bulk sub-horizontal flattening along the east-west Z-axis following KD1. KD2 formed variably-dipping and mutually overprinting reverse and strike-slip shear zones, upright, tight-isoclinal folds and plane strain similar to 12:3:1 marker clasts. The strain studies indicate the primary role of constrictional. strains during the transpressional deformation and the smaller degree of flattening recorded in the amphibolite to granulite facies shear belt. The size of this Proterozoic shear belt is akin to those of modern orogens involved in significant plate reorganisation. (C) 2001 Elsevier Science Ltd. All rights reserved.