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[1] We present a new wavelet transform method to map spatial variations in effective elastic thickness T e and plate loading ratio f. The method assumes a model of thin plate flexural isostasy to describe the mechanical response of the lithosphere to vertical loading. In this model, the rheological properties of the lithosphere are aggregated into the effective elastic thickness T e of an equivalent thin plate overlying an inviscid fluid. A number of methods have been developed to map spatial variations in T e in an attempt to assess regional patterns of flexural strength. Our new method first obtains local coherence and local admittance through wavelet cross-spectral analysis of surface topography and Bouguer gravity anomaly. Wavelet coherence is used to obtain the local characteristic wavelength, which is a function of both T e and the degree of relative loading f of the plate by subsurface loads and surface loads (loading is the combined effect of erosion, sedimentation, intrusion, faulting, and metamorphism). Wavelet admittance, in a normalized form, is used to resolve this f À T e ambiguity, and maps are made of the spatial variations in T e and f. We carry out extensive tests of the wavelet method on simulated topography and Bouguer gravity anomaly data that we generate through finite difference simulations of flexural isostasy with spectrally realistic loads and simple spatial variations in T e . These tests demonstrate that the wavelet inversion method is reasonably robust to uncertainties in loading and in crustal thickness and is able to recover T e to within ±25-50% of its correct value. We apply the wavelet method to southern Africa and recover estimates of T e principally in the range 25-50 km, in good agreement with existing estimates from forward modeling and Fourier coherence analyses. We find that our T e estimates often exceed estimates of crustal thickness, pointing to a strong upper mantle in parts of southern Africa. Citation: Stark, C. P., J. Stewart, and C. J. Ebinger, Wavelet transform mapping of effective elastic thickness and plate loading: Validation using synthetic data and application to the study of southern African tectonics,

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Summary Seismic reflection profiles and gravity anomaly data have been used to determine the structure and evolution of the Namibian continental margin. In comparison to other margins, the gravity anomaly at the Namibian margin shows a number of distinctive features. It lacks an offshore gravity ‘low’, and, despite the presence of up to 9 km of sediments, the gravity ‘high’ is displaced landwards of the maximum sediment thickness. In an attempt to explain these features, the Early Cretaceous–Recent stratigraphic record is analysed using a combined 3‐D backstripping and gravity modelling tech‐nique that enables constraints to be placed on the long‐term mechanical properties of the lithosphere. A neutral depth of necking and a relatively high flexural rigidity (or equivalent elastic thickness, Te, of ~ 25 km) can explain part of the anomaly, at least in the south of the margin. However, large residual anomalies exist that can be reduced by the presence of pre‐rift low‐density sediments within the zone of maximum stretching, south of 22° S, high‐density volcanic material at the eastern pinch‐out of the lower rift sequence and a lateral sediment density variation across the shelf, slope and rise. In addition, the presence of a magmatic body at the base of the crust, provided that the flexural strength of the margin is high, significantly improves the fit between observed and calculated gravity anomalies. Recovered stretching factors enable predictions of the geometry of the Moho to be made. Palaeobathymetry is estimated along the entire margin through time by comparing the subsidence determined from backstripping to that predicted by simple models of rifting. These estimates are within the errors of observed palaeowater depths where well control exists. The requirement of high Te rather than Te that increases with time suggests that stretched continental crust extends offshore for some distance and the continent–ocean boundary occurs in relatively deep water near magnetic anomaly M4. Reconstruction of the gravity field of the South Atlantic at 100 Ma illustrates that, in terms of their gravity signature, the South Atlantic margins are asymmetric.