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Abstract
Thrust Tectonic Styles of the Intracratonic Alice Springs and Petermann Orogenies, Central Australia
T. Flottmann,1 M. Hand,2 D. Close,3 C. Edgoose,3 I. Scrimgeour3
1Santos Ltd., Brisbane, Queensland, Australia
2Department of Geology and Geophysics, University of Adelaide, Adelaide, South Australia, Australia
3Northern Territory Geological Survey, Alice Springs, Northern Territory, Australia
ACKNOWLEDGMENTS
We thank the Central Lands Council for permission to access Aboriginal land in the Petermann Ranges. T. Flottmann and M. Hand are grateful for logistic support provided by the Northern Territory Geological Survey, with special thanks to Peter Crispe and Max Heggen. The chapter benefited from discussions with Fabrizio Storti, Russell Korsch, Mike Sandiford, and Dave Warner. Reviews by Rick Allmendinger, Tomas Zapata, Ken McClay, and an anonymous reviewer helped clarify and focus the chapter.
ABSTRACT
The Petermann and Alice Springs orogens are late Neoproterozoic to early Cambrian and middle Paleozoic intracratonic fold-and-thrust belts that shaped the Amadeus Basin in Central Australia. Displacements during both orogenies were accommodated in the footwalls of crustal-scale fault systems. The deformational style is characterized by basement-involved triangle zones in which displacement is partitioned into two mechanical units. A lower succession is characterized by basinward thrusting and an upper succession with hinterland-directed displacement. The interleaving of basement and cover units within the basin-directed wedges is a reflection of the relatively low mechanical contrast between cover successions and basement. North-vergent shortening during the Petermann orogeny exceeded 100 km, the bulk of which was accommodated by dramatic thickening, which led to burial of the Amadeus Basin sequences deeper than 20 km. Despite the thickening, there was little foreland-basin development, suggesting that the lithosphere may have been too weak to form a long-wavelength flexure. Along the northern margin of the Amadeus Basin, the Alice Springs orogeny was associated with as much as 50 km of shortening that can be resolved into two phases: (1) south-directed, basinward overthrusting of a basement wedge and (2) underthrusting that led to the development of a large-displacement north-vergent passive back thrust within the northern Amadeus Basin. This back thrusting led to the formation of structural hydrocarbon traps that developed along the southern flank of a progressively narrowing and deepening foreland flexure. Our study provides a kinematic framework for basin-shaping deformation along the margins of the Amadeus Basin and suggests that future hydrocarbon exploration in the Central Australian basins should assess the implications of the style of basement-cover interaction, as highlighted by the structural styles of both the Petermann and Alice Springs orogenies.
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