Evolution of deep-water rifted margins: Testing depth-dependent extensional models

A general understanding of rifted margins, which form by thinning of the continental lithosphere, exists. Nevertheless, the exact form of thinning is unclear. This debate has been stimulated by acquisition of dense seismic wide-angle and deep reflection surveys from Atlantic Ocean margins. A central issue concerns the way in which thinning changes with depth. We have tackled this issue by developing a generalized inverse model. This model attempts to fit subsidence and crustal thinning observations by varying strain rate as a function of time and space. Depth-dependent thinning is permitted but we do not prescribe its existence or form. Here, the algorithm is applied to six margins, including two of the most contentious conjugate margins: Newfoundland-Iberia and Brazil-Angola. Calculated strain rate histories predict thinning estimates which broadly match estimates inferred from normal faulting. The Eastern Indian and Beaufort Sea margins formed by largely uniform lithospheric thinning. In contrast, the Newfoundland-Iberian conjugate margins formed by a pattern of strongly depth-dependent strain rate. To account for the paucity of syn-rift decompression melting of the underlying asthenosphere, the lithospheric mantle close to oceanic-continent transition must thin more slowly than the overlying crust. This form of depth dependency is not common. For example, the Brazil-Angolan conjugate margin could have formed by uniform lithospheric thinning provided thick layers of salt were deposited in a preexisting 400 m deep topographic depression. Depth-dependent thinning is not required to account for rapid subsidence of presalt strata. Citation: Crosby, A. G., N. J. White, G. R. H. Edwards, M. Thompson, R. Corfield, and L. Mackay (2011), Evolution of deep-water rifted margins: Testing depth-dependent extensional models, Tectonics, 30, TC1004, doi: 10.1029/2010TC002687.