Post-Breakup Rifted Margin Hinterland Uplift Predicted from a Geodynamic Model of Continental Lithosphere Thinning and Breakup

Erica Greenhalgh and Nick J. Kusznir
Earth and Ocean Sciences, University of Liverpool, Liverpool, United Kingdom

Post-breakup uplift of the continental hinterland has been observed along many rifted margins. Hinterland uplift, located continental-ward of rifted continental margin lithosphere thinning and subsidence, has a width of several hundred kilometres and an observed amplitude of the order of 1 - 1.5 km. Evidence suggests that uplifted rifted margin hinterlands have experienced multiple post-breakup uplift events, with the initial phase generally associated with continental breakup and later phases significantly post-dating rifting. Post-breakup uplift of passive margin continental hinterlands is predicted by a geodynamic model of continental breakup incorporating lithosphere thinning by simultaneous pure-shear and buoyancy assisted upwelling. The resultant flow field within continental lithosphere and asthenosphere has an increased ratio of upwelling velocity to divergent velocity (Vz/Vx) compared to a simple passive pure-shear lithosphere thinning model. This produces an outward flow of asthenosphere material towards the young continental margin lithosphere, thickening the adjacent continental lithosphere at distances beyond the region of localised continental breakup thinning and decreasing the lithosphere geothermal gradient. Re-equilibration of the geotherm causes warming and uplift of the thickened continental lithosphere inward of the rifted margin. The uplift of the continental hinterland is further amplified by isostatic rebound in response to erosion. The model predicts post-breakup hinterland uplift of amplitude up to 1 km and wavelength 300 km, located inboard of the region of continental lithosphere thinning. Results show that the Vz/Vx ratio of upwelling material due to induced buoyancy during early sea-floor spreading is the dominant control on the predicted thermal uplift.

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