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Abstract

Comparison of structural and paleothermal elements of the U. S. central Atlantic passive continental margin supports previous suggestions that continental rifting tends to be asymmetrical in cross-section, periodically shifting from one sense of asymmetry to the other along strike. Our analysis indicates that inflections in the sinusoidal trace of the basement hinge zone define segments of the rifted margin with opposing asymmetry. Hinge zone embayments lie on the proximal side of rift asymmetry, whereas the salients are distal. Asymmetry is expressed by(l) the predominant tilt direction of synrift normal fault blocks and (2) synrift and postrift subsidence and uplift patterns both onshore and offshore. In contrast, the positions of the shelf-slope break, fall line, prerift orogenic front, coastline and oceanic fracture zones correlate imperfectly to poorly with rift architecture. Although the subsidence and thermal history of some offshore sedimentary basins is adequately explained by an instantaneous uniform stretching model, only asymmetrical strain accounts for the uplift and subsidence patterns for the margin as a whole, particularly if onshore subsidence patterns are considered. Although not as well understood, major aspects of the conjugate northwest African margin are compatible with the model.

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