Figure 173-5. Cartoon incorporating available drill core and geophysical evidence into a single integrated model for the evolution of the Iberia Abyssal Plain margin. As high level extension was accommodated along a detachment fault, upwelling of asthenosphere in response to "pure-shear" extension at depth caused melting and intrusion of lower crust in the transition zone. Intrusion probably continued during subsequent block-faulting which dissected the lower plate to the detachment fault. Drilling during Leg 174A will test this model by investigating the nature of crust in the transition zone and testing the detachment hypothesis.
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