Some remarks on the relation between vertical motions of the lithosphere during extension and the necking depth parameter inferred from kinematic modeling studies

A well-established fact of continental stretching is that during the extens ion phase the lithosphere retains a finite (flexural) strength. Vertical lo ads caused by the redistribution of material with crustal and mantle densit ies during lithospheric thinning can therefore be supported by the lithosph ere. Whether these loads cause flexural uplift or subsidence depends on the strength distribution within the continental lithosphere. In kinematic mod el studies, stratigraphic and other data acquired in the vicinity of sedime ntary basins and passive margins are "inverted" for these loads. In these m odels, vertical rebound loads are parameterized in terms of a "necking dept h" parameter. We use thermal-mechanical finite element simulations to inves tigate whether rheological information about the continental lithosphere ca n be extracted from the necking depth parameter derived from kinematic mode ls. We conclude that spatial and temporal variations in necking depths near basin edges and passive margins as derived from our dynamic simulations ar e not consistent with the uniform and stationary necking depth that is usua lly assumed in kinematic models. This is very important since, typically, t he stratigraphic data used in kinematic model studies are acquired in these regions. We therefore conclude that there is no one-to-one relation betwee n the necking depth parameter and the strength distribution in the lithosph ere.