Abstract

The Early Eocene magma-rich northeast Atlantic rifted margins contain a large number of pre-breakup and post-breakup compressional structures, located in abandoned Early Cretaceous hyperextended basins with crustal stretching factors of 3–4 or more. The deformation both predates and postdates the magma-rich breakup. The hyperextended basins are often underlain by high-velocity lower crustal bodies, which we argue represent partially serpentinized upper mantle. Long-lived lithospheric weakening and proneness to deformation is proposed to relate to crustal hyperextension, probably enhanced by mantle hydration.

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