MAGSAT investigations over the greater African region
Abstract
A high-resolution, wide-band MAGSAT total intensity magnetic anomaly map of the greater African region has been prepared that is useful for constraining regional geologic and tectonic interpretations. Magnetic anomaly discrepancies in the MAGSAT dawn and dusk orbital cross-overs (mis-ties) are used to establish improved data selection criteria and problem-oriented data processing techniques. Empirical and random data handling techniques have been developed to minimize both the spatially coherent and random errors in the data. The processing has yielded wide-band dawn and dusk orbital MAGSAT data sets of the greater African region which have substantially reduced dawn-dusk discrepancies compared to other published wide-band maps. High correlation between the two data sets suggests that they are internally consistent, relatively free from external field effects, and hence, useful for broad-scale lithospheric magnetic anomaly interpretation. The ridge-regression method has been used in a large-scale equivalent source inversion of MAGSAT data. The optimum damping parameter is selected based on the rate of increase of the variance in the residual between the observed and the calculated anomaly and the variance of the solution for a series of damping parameters. Solutions obtained by the damping parameter selected in this manner are numerically stable and geologically meaningful. Consequently, these solutions can be used in various applications such as transformation into effective magnetic susceptibility variation and differential reduction-to-pole. There is a high degree of correspondence between MAGSAT anomalies and regional Euro-African geotectonic provinces. Moreover, the visually inferred differences in magnetic contrasts between shields and basins, shields and Phanerozoic foldbelts, and oceanic uplifts and the remaining ocean floor have been found to be statistically significant. Comparison of the high-resolution Afro-South American radially-polarized MAGSAT anomalies suggest that the Pangea reconstruction is a useful regional satellite magnetic anomaly verification tool. Furthermore, the consistency of MAGSAT magnetic contrasts and the geologic processes on the conjugate plates provide significant constraints for the geologic interpretation of the anomalies. In addition, three-dimensional quantitative magnetic models constrained by available geologic and geophysical data have been generated for West Africa, Central Africa, Southern Africa, Europe, and Northeastern Walvis Ridge that demonstrate the utility of the MAGSAT maps in regional geotectonic studies.
Degree
Ph.D.
Advisors
Hinze, Purdue University.
Subject Area
Geophysics|Remote sensing
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