The South Falkland basin is a partially filled Cenozoic foreland basin located south of the Falkland Plateau. It was formed by flexure of this southern edge of the South American plate when the load represented by Burdwood Bank collided. This continental fragment belongs to the predominantly oceanic Scotia plate. Flexure probably started in early Cenozoic times and has continued to the present day. The whole region is submarine and so the detailed stratigraphy and structure of the basin has been well imaged by seismic reflection profiling. The clarity of this imagery has made analysis of structures within the collision zone possible. The plate boundary itself is an active oblique thrust fault which has controlled the growth of a frontal fold. There is evidence for older phases of thrusting and folding further south. Within and beneath the sediments which blanket the flexed South American plate, normal faulting occurs on a variety of scales. Episodes of stratigraphic growth associated with the largest of these faults demonstrates that they were active during flexural bending. We have modeled the development of the South Falkland basin using two different approaches, both of which are based upon the simplest elastic model. Inverse modeling of free‐air gravity and bathymetric profiles suggest that the elastic thickness of the loaded crust is 5–20 km. A complementary approach based upon the spectral analysis of free‐air gravity and bathymetry shows that the elastic thickness is 15 ± 5 km. Both techniques indicate that the flexed continental lithosphere is weak, a conclusion supported by the presence of normal faults within the flexed plate. A small increase in elastic thickness from west to east appears consistent with a change in the density and penetration of normal faulting.

[1] We reassess the variation of elastic thickness as a function of lithospheric plate age using a global database of bathymetric and free-air gravity profiles which are perpendicular to oceanic trenches. As in many previous studies, our starting point is the well-known floating elastic plate model. In order to remove the influence of short-wavelength features not associated with lithospheric bending, adjacent profiles from 10-Myr bins have been stacked together to construct average profiles with standard deviations. Each average profile was then inverted in a two-stage procedure. First, singular value decomposition was used to determine two unknown flexural parameters, together with a regional slope and offset, for any given elastic thickness. This procedure was repeated for a range of elastic thicknesses. Second, residual misfit was plotted as a function of elastic thickness, and the global minimum was identified. This two-stage procedure makes no prior assumptions about magnitude of the load, size of the bending moment, or whether the elastic plate is broken/continuous. We obtained excellent fits between theory and observation for both bathymetric and gravity profiles from lithosphere with an age range of 0-150 Ma. The shape of the residual misfit function indicates the degree of confidence we have in our elastic thickness estimates. The lower limit of elastic thickness is usually well determined but upper limits are often poorly constrained. Inverse modeling was carried out using a range of profile lengths (250-300, 500, and 700 km). In general, our estimates show no consistent increase of elastic thickness as a function of plate age. This surprising result is consistent with recent reassessments of elastic thickness beneath seamounts and implies either that elastic thickness is independent of plate age or that elastic thickness cannot be measured with sufficient accuracy to reveal such a relationship. Modeling of short free-air gravity profiles (250-300 km) does tentatively suggest that elastic thickness increases linearly from 5 to 10 km between 0 and 20 Ma and from 10 to 15 km between 20 and 150 Ma. This variation roughly matches the depth to the 200°C isotherm which corresponds to an homologous temperature of 0.4 for wet peridotite. Unfortunately, for longer profile lengths, there is no temporal dependence, and elastic thicknesses vary considerably for all plate ages. Bathymetric profile modeling yields similar results although uncertainties are larger.