Transfer zones normal and oblique to rift trend: examples from the Perth Basin, Western Australia
Tingguang Song, Peter A. Cawood, Mike Middleton, 2001. "Transfer zones normal and oblique to rift trend: examples from the Perth Basin, Western Australia", Non-Volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea, R. C. L. Wilson, R. B. Whitmarsh, B. Taylor, N. Froitzheim
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The Perth Basin is a major tectonic province along the western margin of the Australian continent. Basin morphology is controlled by north-striking faults formed during Permian rifting and reactivated during later tectonic events, notably during continental break-up in Late Jurassic–Early Cretaceous time. Transfer structures, including those normal and oblique to the major faults, compartmentalized the basin into segments of distinctive character. East-west transfer faults, perpendicular to the basin trend, were active throughout the rift stage of basin development and are recognized only in the northernmost onshore part of the Perth Basin, corresponding to the depocentre for Permian sediment accumulation. Northerly trending normal faults change in character and/or terminate at these east-west structures. The NW-striking transfer zones influenced deformational features formed during the Late Jurassic–Early Cretaceous break-up. No continuous fault plane has been identified with these zones in the sedimentary sequences. They are characterized by the termination and/or swing of major normal faults at the transfer zones. Sinistral strike-slip movement of at least 16 km is recognized across the Abrolhos Transfer Zone on the basis of offset in the trend of the Beagle Fault system. The orientation, age of activation, and position of these zones are similar to those of transform faults in the adjoining Indian Ocean, suggesting that the two structures are contiguous.
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Non-volcanic continental margins may form up to 30% all present-day passive margins, and remnants of them are preserved in mountain belts. The papers in this volume demonstrate the benefits of integrating offshore and onshore studies, and illustrate the range of information obtained at different scales when comparing evidence from land and sea. Data sets collected across a range of spatial scales are evaluated: thin sections, cores, outcrops, seismic reflection profiles, and other geophysical data. The outcrop scale is crucial because it enables the spatial gulf to be bridged between DSDP and ODP cores and marine seismic data. There is also the problem that basins on land and beneath the sea inevitably have had different post-rift histories resulting in their contrasting present-day elevation. In mountain belts, portions of continental margins and oceanic crust are superbly exposed, but dismembered by subsequent compressional tectonics. Off present-day passive margins, extensional features have only been slightly deformed, if at all, by compressional movements, but are buried beneath significant thicknesses of post-rift sediments and so can only be sampled by ocean drilling at a small number of points.
The first paper reviews the synergies that have occurred between investigations of the eastern North Atlantic non-volcanic margins and remnants of similar Mesozoic margins preserved in the Alps, and some later papers return to this theme. However, papers describing margins from other parts of the world show that it may be premature to use models based on the Atlantic and the Alps as the paradigm for all non-volcanic margins. The following 25 papers in the book are grouped under the following headings: (1) Margin overviews; (2) Exhumed crust and mantle; (3) Tectonics and stratigraphy; (4)Numerical models of extension and magmatism.