Figure 3. Modeled stratigraphic and structural response to lithospheric extension. A) Sag basin development characterized by mid-crustal detachments that facilitate lower crustal and lithospheric mantle in the absence of upper crustal extension. B) Normal rift basin development when lithosperic extension involves both the crust and lithospheric mantle. C) Complicating effects when earlier brittle deformation is overprinted by later plastic rifting of the lower crust and lithospheric mantle. This configuration poses a problem because the syn-rift sag phase is easily misinterpreted as simply the post-rift sedimentation associated with the first phase of rifting (modified from Driscoll & Karner, 1998; Karner & Driscoll, 1999). While thinning of the lithospheric mantle generates transient uplift, crustal extension creates permanent accommodation.