Mapping the Thermal Structure of Southern Africa From Curie Depth Estimates Based on Wavelet Analysis of Magnetic Data With Uncertainties

Surface heat flow provides essential information on the thermal state and thickness of the lithosphere. Southern Africa is a mosaic of the best‐preserved and exposed crustal blocks, assembled in the early late Archean and then modified by a series of major tectono‐thermal events, both of Precambrian and Phanerozoic. Understanding the thermal and compositional structure of the southern African lithosphere provides crucial information for the actual causes, processes of lithospheric stability, and modification. Curie depth, interpreted as the depth to 580°C, provides a valuable constraint on the thermal structure of the lithosphere. Due to the sparse distribution of surface heat flow data, we examine the degree to which the thermal structure of the crust can be constrained from Curie depth estimates in southern Africa. We provide a Curie depth map for southern Africa (obtained from the inversion of magnetic anomaly data via power spectral methods and wavelet analysis) alongside with a heat flow map (based on the previous Curie depth estimates), both equipped with uncertainties via a Bayesian approach. Opposed to other cratonic regions, the observation of a shallow Curie depths and low heat flow over the Kaapvaal Craton suggests a thermochemical reworking of the cratonic lithosphere in this region. Furthermore, a comparison with a model for the Moho depth reveals significant variations of the Curie depth, which may be located below or above the Moho in large regions. Both observations indicate that in certain regions magnetic anomaly based Curie depth estimates may reflect a compositional rather than a temperature controlled constraint.
Plain Language Summary: The thermal state and thickness of the lithosphere are reflected, among other quantities, in the surface heat flow. While heat flow data are rather sparse, magnetic anomaly maps are widely available and allow, under certain conditions, the estimation of the bottom of the magnetized layer within the lithosphere. Latter can be associated with the 580°C‐isotherm (frequently called the Curie depth), therefore allowing inferences on the thermal state of the lithosphere from magnetic data. Here, we use classical power spectral methods in combination with wavelet analysis and Bayesian methods to estimate the Curie depth and its uncertainty from magnetic anomaly maps, and subsequently, use it to estimate the surface heat flow over southern Africa. Comparison with the sparsely available measured heat flow allows us to assess the quality of the estimation and to interpret it with respect to the lithospheric structure. Southern Africa is particularly suitable for such a study due to its well‐preserved and well‐studied crustal blocks. The shallow Curie depths and low heat flow observed over the Kaapvaal Craton suggest a thermal reworking of the old lithospheric structures in this region. Comparison with a Moho depth model further suggests that in some regions the obtained Curie depth estimates do not necessarily reflect a temperature controlled but rather a compositional boundary.
Key Points: Curie depth is estimated over southern Africa via power spectral methods and wavelet transforms within a Bayesian framework. Heat flow and its uncertainty is estimated based on Curie depth. Shallow Curie depth and low heat flow suggest thermochemical reworking of the Kaapvaal Craton.
Bundesministerium für Wirtschaft und Energie (BMWi) http://dx.doi.org/10.13039/501100006360
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) http://dx.doi.org/10.13039/501100003246