The discovery of hyperthinned continental crust and exhumed mantle on present-day deep-water rifted margins leads to two fundamental questions: (1) in detail, how does the crust thin in extension, and (2) what controls extreme crustal thinning and mantle exhumation? Reflection and refraction seismic lines across the Iberian margin show decoupling levels in the crust cut by structures that eventually transfer deformation to mantle levels. The region of decoupled extension appears to be more broadly distributed on the northern Iberian margin and more localized on the southern margin. Based on drill hole data, the transition from decoupled to coupled deformation occurred during Tithonian time (ca. 145 Ma). This evolution from decoupled to coupled deformation may help explain the crustal architecture of the Iberian margin. An apparent delay of subsidence across the hyperextended coupled zone of the Iberian margin may indicate that crustal thinning had to occur simultaneously with lithospheric necking and the advection of heat related to lithospheric mantle thinning.

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