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Solid Earth An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/se-2018-9
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
07 Feb 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).
Inverted distribution of ductile deformation in the relatively “dry” middle crust across the Woodroffe Thrust, central Australia
Sebastian Wex1, Neil S. Mancktelow1, Friedrich Hawemann1, Alfredo Camacho2, and Giorgio Pennacchioni3 1Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland
2Department of Geological Sciences, University of Manitoba, 125 Dysart Rd, Winnipeg, Manitoba, R3T 2N 2, Canada
3Department of Geosciences, University of Padova, Via Gradenigo 6, 35131 Padova, Italy
Abstract. Thrust fault systems typically distribute shear strain preferentially into the hanging wall rather than the footwall. In this paper, we present a regional-scale example that does not fit this model. The Woodroffe Thrust developed due to intracontinental shortening during the Petermann Orogeny (ca. 560–520 Ma) in central Australia. It is interpreted to be at least 600 km long in its general E-W strike direction, with an approximate top-to-north minimum relative displacement of 60–100 km. The associated mylonite zone is most broadly developed in the footwall. The immediate hanging wall was only marginally involved in mylonitization, as can be demonstrated from the contrasting thorium signatures of the upper amphibolite facies footwall and the granulite facies hanging wall protoliths. Thermal weakening cannot account for such an inverse deformation gradient, as syn-deformational P-T estimates for the Petermann Orogeny in the hanging wall and footwall from the same locality are very similar. The distribution of pseudotachylytes, which act as preferred nucleation sites for shear deformation, also cannot provide an explanation, since these are prevalent in the immediate hanging wall. The most likely reason for the inverted deformation gradient across the Woodroffe Thrust is water-assisted weakening due to the increased, but still limited, presence of aqueous fluids in the footwall. On the contrary, the presence or absence of aqueous fluids does not appear to be linked to the regional variation in mylonite thickness, which generally increases with increasing metamorphic grade.
Citation: Wex, S., Mancktelow, N. S., Hawemann, F., Camacho, A., and Pennacchioni, G.: Inverted distribution of ductile deformation in the relatively “dry” middle crust across the Woodroffe Thrust, central Australia, Solid Earth Discuss., https://doi.org/10.5194/se-2018-9, in review, 2018.
Sebastian Wex et al.
Sebastian Wex et al.
Sebastian Wex et al.

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