Lithospheric delamination during rifting

Depth dependent thinning of continental lithosphere whereby the mantle lithosphere has thinned more than the crustal layer is observed across conjugate rifted margins. Rifted margins form after extension of continental lithosphere whereby the crust and mantle parts of the lithosphere should have been thinned an approximately equal amount. The fact that mantle lithosphere thinning often exceeds crustal thinning suggests that other geodynamic processes must be at work during the late syn-rift to early post breakup phase. Here we present a model for conjugate margin formation in which the apparent discrepancy between the amount of crustal and mantle lithosphere extension is explained by removal of mantle lithosphere (delamination) through the formation of a lithospheric drip. Lithospheric material feeds laterally into the drip which eventually is removed and recycled into the asthenosphere. Further sinking of the drip induces a counter flow from the transition zone that brings up damp transition mantle into the rift, and may create upper mantle plumes.