Mid to late Paleozoic shortening pulses in the Lachlan Orogen, southeastern Australia: a review

ABSTRACT

In the late Silurian, the Lachlan Orogen of southeastern Australia had a varied paleogeography with deep-marine, shallow-marine, subaerial environments and widespread igneous activity reflecting an extensional backarc setting. This changed to a compressional–extensional regime in the Devonian associated with episodic compressional events, including the Bindian, Tabberabberan and Kanimblan orogenies. The Early Devonian Bindian Orogeny was associated with SSE transport of the Wagga–Omeo Zone that was synchronous with thick sedimentation in the Cobar and Darling basins in central and western New South Wales. Shortening has been controlled by the margins of the Wagga–Omeo Zone with partitioning along strike-slip faults, such as along the Gilmore Fault, and inversion of pre-existing extensional basins including the Limestone Creek Graben and the Canbelego–Mineral Hill Volcanic Belt. Shortening was more widespread in the late Early Devonian to Middle Devonian Tabberabberan Orogeny, with major deformation in the Melbourne Zone, Cobar Basin and eastern Lachlan Orogen. In the eastern Melbourne Zone, structural trends have been controlled by the pre-existing structural grain in the adjacent Tabberabbera Zone. Elsewhere Tabberabberan deformation involved inversion of pre-existing rifts resulting in a variation in structural trends. In the Early Carboniferous, the Lachlan Orogen was in a compressional backarc setting west of the New England continental margin arc with Kanimblan deformation most evident in Upper Devonian units in the eastern Lachlan Orogen. Kanimblan structures include major thrusts and associated fault-propagation folds indicated by footwall synclines with a steeply dipping to overturned limb adjacent to the fault. Ongoing deformation and sedimentation have been documented in the Mt Howitt Province of eastern Victoria. Overall, structural trends reflect a combination of controls provided by reactivation of pre-existing contractional and extensional structures in dominantly E–W shortening operating intermittently from the earliest Devonian to Early Carboniferous.

KEYWORDS:

• Carboniferous
• Devonian
• Lachlan Orogen
• orogeny
• southeastern Australia
• shortening
• subduction

Acknowledgements

I have benefited from discussions with many people, including: Gary Burton, Ross Cayley, Bob Henderson, Evan Leitch, Robin Offler, Gordon Packham, Laurie Sherwin, Tony Wright and no doubt others who I have failed to mention. Support has been provided by the University of Wollongong (GeoQuEST Research Centre). I am most grateful to Evan Leitch for reading over the final draft and making many useful suggestions that have improved the manuscript. The final manuscript has been significantly improved following suggestions of the journal reviewers Gary Burton and David Gray.

Disclosure statement

No potential conflict of interest was reported by the author.