Geometry of a large‐scale, low‐angle, midcrustal thrust (Woodroffe Thrust, central Australia). Issue 11 (13th November 2017)

• Record Type: Journal Article
• Authors: Wex, S.; Mancktelow, N. S.; Hawemann, F.; Camacho, A.; Pennacchioni, G.
• Is Part Of: Tectonics. Volume 36:Issue 11(2017)
• Page Start: 2447
• Page End: 2476
• Publication Date: 2017-11-13
• Subjects: Woodroffe Thrust -- Musgrave Block -- low‐angle thrust -- pseudotachylyte -- middle crust -- underthrusting; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1002/2017TC004681
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: The Musgrave Block in central Australia exposes numerous large‐scale mylonitic shear zones developed during the intracontinental Petermann Orogeny around 560–520 Ma. The most prominent structure is the crustal‐scale, over 600 km long, E‐W trending Woodroffe Thrust, which is broadly undulate but generally dips shallowly to moderately to the south and shows an approximately top‐to‐north sense of movement. The estimated metamorphic conditions of mylonitization indicate a regional variation from predominantly midcrustal (circa 520–620°C and 0.8–1.1 GPa) to lower crustal (~650°C and 1.0–1.3 GPa) levels in the direction of thrusting, which is also reflected in the distribution of preserved deformation microstructures. This variation in metamorphic conditions is consistent with a south dipping thrust plane but is only small, implying that a ≥60 km long N‐S segment of the Woodroffe Thrust was originally shallowly dipping at an average estimated angle of ≤6°. The reconstructed geometry suggests that basement‐cored, thick‐skinned, midcrustal thrusts can be very shallowly dipping on a scale of many tens of kilometers in the direction of movement. Such a geometry would require the rocks along the thrust to be weak, but field observations (e.g., large volumes of syntectonic pseudotachylyte) argue for a strong behavior, at least transiently. Localization on a low‐angle, near‐planar structure that crosscuts lithological layers requires a weak precursor, such as a seismic rupture in the middle to lower crust. If this was a single event, the intracontinental earthquake must have been large, with the rupture extending laterally over hundreds of kilometers. Key Points: The Woodroffe Thrust preserves a midcrustal to lower crustal shearing history in the central Musgrave Block The syndeformational geometry of the thick‐skinned Woodroffe Thrust was shallowly dipping (≤6°) over ≥60 km in the direction of thrusting Intracontinental shortening in Australia at circa 560–520 Ma was in part accommodated by in‐sequence underthrusting