Australia: The Land Where Time Began

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Western Gawler Craton, Australia Shear Zone architecture in the Christie Domain, Geophysical Appraisal of an Orogenic Terrain that is Poorly Exposed

In the Christie Domain of the northwest Gawler Craton, southern Australia large-scale crustal shear zones of Proterozoic age are partially exposed from beneath cover sequences. These structures are allowed to be mapped under cover and the evaluation of their 3-D geometry and kinematics by their being associated with gravity and magnetic anomalies. It is indicated by gravity and magnetic modelling that these shear zones form an imbricate oblique thrust stack with a combined-to-the southeast, left-lateral transport. The longest shear zones in the stack penetrate to at least 15 km into the crust, dipping to the northwest at 70o; their inferred sense of motion are consistent with kinematic indicators from sparse outcrops. The stack includes crustal slices that are bound by the Karari Fault Zone, Tallacootra and Blowout Shear Zones, Colona and Coorabie Fault Zones and the Muckanippie Shear Zone, from the northwest to the southeast. Discrete tectonometamorphic packages are separated by these structures within the Christie Gneiss, which was previously undifferentiated, of the Mulgathing Complex of Archaean age, which implies several generations of the transport of material from the lower crust to the middle crust.

The Muckanippie Shear Zone, which is a second-order splay of the Coorabie Fault Zone, as is indicated by 3-D inversion of gravity data, has an antithetic dip to the southeast, and is part of a positive flower structure.

When coupled with recent reconnaissance geochronology, cross-cutting relationships suggest that the western Gawler Craton is part of the Mawson Continent, was under an oblique slip deformational regime which was long lasting, after about 1,590 Ma. This tectonic reworking correlates with episodic pervasive metamorphism, and deformation that has been recorded elsewhere in the Gawler Craton between about 1,550 and 1,450 Ma (Coorabie Orogeny), which points to a complex history of stabilisation in Proterozoic Rodinia.

Mesozoic age rift faults of the Southern Rift System cut the Tallacootra, Colona and Coorabie structures at high angle to their strikes, and may form piercing points in reconstructions of Gondwana, as well as earlier Rodinia configurations.

Sources & Further reading

  1. Direen, N. G., A. G. Cadd, P. Lyons and J. P. Teasdale (2005). "Architecture of Proterozoic shear zones in the Christie Domain, western Gawler Craton, Australia: Geophysical appraisal of a poorly exposed orogenic terrane." Precambrian Research 142(12): 28-44.


Author: M. H. Monroe
Last Updated 27/04/2015
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