Authors / CoAuthors
Czarnota, K. | White, N. | Fishwick, S.
Abstract
The subsidence histories of most, but not all, basins can be elegantly explained by extension of the lithosphere followed by thermal rethickening of the lithospheric mantle to its pre-rift thickness. Although this model underpins most basin analysis, it is unclear whether subsidence of rift basins developed over thick lithosphere follows the same trend. Here the subsidence history of the Caning rift basin of Western Australia is modelled which putatively overlies lithosphere - 180 km thick, imaged using shear wave tomography. The entire subsidence history of the, < 300 km wide and <6 km thick, western Canning Basin is adequately explained by Ordovician rifting of ~120 km thick lithosphere followed by post-rift thermal subsidence as described by the established model. In contrast, the < 150 km wide and 15 km thick Fitzroy Trough of the eastern Canning Basin, reveals an almost continuous phase of normal faulting between Ordovician and Carboniferous Periods followed by negligible post-rift thermal subsidence which cannot be accounted for by the established model. This difference in basin architecture is attributed to rifting of thick lithosphere constrained by the presence of diamond bearing lamproites intruded into the basin depocentre at ~20 Ma. In order to account for the observed subsidence, at standard crustal densities, the lithospheric mantle is required to be depleted by 50-70 kg m-3. The actual depletion of the lowermost lithospheric mantle was assessed by modelling REE concentrations of the ~20 Ma lamproites along with other ultrapotassic rocks from the Kimberley, Yilgarn and Pilbara blocks which reveal a depletion of 40-70 kg m-3. Together these results suggest that thinning of thick lithosphere to thicknesses > 120 km is thermally stable and is not accompanied by post-rift thermal subsidence driven by thermal rethickening of the lithospheric mantle. The discrepancy between estimates of lithospheric thickness derived from subsidence data in the Western Canning and that derived from shear wave tomography suggests that the latter technique cannot resolve lithospheric thickness variations on < 300 km half wavelengths.
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nonGeographicDataset
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77720
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- External Publication
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2013-01-01T00:00:00
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