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 extension phase the lithosphere retains a finite (flexural) strength. Vertical loads caused by the redistribution of material with crustal and mantle densities during lithospheric thinning can therefore be supported by the lithosphere. Whether these loads cause flexural uplift or subsidence depends on the strength distribution within the continental lithosphere. In kinematic model studies, stratigraphic and other data acquired in the vicinity of sedimentary basins and passive margins are "inverted" for these loads. In these models, vertical rebound loads are parameterized in terms of a "necking depth" parameter. We use thermal-mechanical finite element simulations to investigate whether rheological information about the continental lithosphere can be extracted from the necking depth parameter derived from kinematic models. We conclude that spatial and temporal variations in necking depths near basin edges and passive margins as derived from our dynamic simulations are not consistent with the uniform and stationary necking depth that is usually assumed in kinematic models. This is very important since, typically, the stratigraphie data used in kinematic model studies are acquired in these regions. We therefore conclude that there is no one-to-one relation between the necking depth parameter and the strength distribution in the lithosphere.