MECHANICS OF LITHOPHERIC DELAMINATION FROM PHYSICAL MODELS

Two suites of lithospheric-scale physical experiments investigate the effect of (1) coupling between the crust and lithospheric mantle and (2) variations of lithospheric density on lithospheric delamination and surface style of deformation. Models with both a strong coupling and net negatively buoyant lithospheric mantle produce narrower belts of surface deformation and deep roots localized near the plate boundary. In contrast, models with both strong coupling and net positively buoyant lithospheric mantle have wider belts of surface deformation and shallow distributed roots. Although surface deformation of models with a weak coupling does not vary with varying the lithosphere's bulk density, the deformation pattern at depth varies: delamination occurs in weakly coupled models having net negatively buoyant lithospheric mantle, whereas models with net positively buoyant lithosphere do not delaminate. For weak-coupling models, the density of the lithosphere is the primary control on the process of syn-collisional delamination.

The thrusting of the excess Indian lithospheric mantle beneath the Eurasian plate margin during Himalayan orogeny is similar to that observed in the models. For the Tibetan Plateau lithosphere, the modeling results imply either a weak coupling between the Tibetan crust and its lithospheric mantle or delamination of the lithospheric mantle from the Tibetan crust. In the Alps and Pyrenees, it is likely that the lithospheric mantle of the non-delaminating plate margins initially contained less net negatively (if not net positively) buoyant mass than the delaminating plate margins .