Seismic depth images show that magma-poor rifted margins between Iberia and Newfoundland are characterized by two different types of detachment that led to the unroofing of a broad expanse of mantle. Low-angle detachments develop in serpentinites at the base of pre-thinned crust and control further crustal thinning. These detachments are cut by large-offset faults, rooting at a steep angle, but with an exhumed slip surface and footwall flexurally rotated to a low angle during unroofing. Successive generations of this second type of detachment lead to the roughly symmetric unroofing of a broad expanse of mantle as new detachments repeatedly cut through the footwall of the preceding detachment, leaving the abandoned root zone as landward-dipping reflectors within exhumed mantle on both sides of the developing rift.

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