Application of magnetic method on the Argentine continental shelf between 35°S and 48°S

Abstract

The total magnetic anomaly (TMA) from a global grid was analysed in order to characterize the magnetic features of the Argentine continental shelf (35°S to 48°S) and to expand the current knowledge of such area. TMA amplitudes within the study area were mathematically filtered and enhanced using various techniques including the analytic signal method, the tilt angle method and the second vertical derivative method. In order to estimate the depths of the magnetic sources on the Tona anomaly and the continental edge, the Euler deconvolution method and a 2-D gravimetric inversion model were applied. The TMA filtering results were used to observe and identify large transform zones such as the Río de la Plata system, the Salado, Ventana, Colorado and Malvinas zones, and other minor systems such as the Rawson transform zones. The San José and El Cortijo crustal sutures were also outlined using the applied methods, and it was possible to map and identify a change in orientation of the Ventania-Cape Fold Belt. The tilt angle method revealed high-frequency patterns in the oceanic crust as a result of its volcanic nature. The second vertical derivative method exhibited high-frequency patterns in the G and Tona anomalies, the M-series magnetic anomalies and oceanic bottom alignments, revealing their volcanic and episodic character through a large and complex distribution of blocks at the continental-oceanic boundary. Discontinuous linear magnetic sources were observed along the ancient Dom Feliciano-Lavalleja shear belt, most of which were calculated by Euler deconvolution to be located at depths of approximately 5000-8000 m. On transform zones, inner alignments and continentaloceanic boundaries, few dipoles associated with fault steps and dykes were identified. The sources of the M-series anomalies were located at depths of 8000-12000 m, whereas abundant deeper sources were identified for the Deseado and Somuncurá massifs and the Mar Argentino rise. The Euler deconvolution method was used to calculate a source depth range for the conspicuous Tona anomaly of 8000-20000 m. In addition, a 2-D gravimetric inversion model based on a NE-trending profile was used to identify a mafic body along the Patagonia-Gondwana suture bounded by a sub-surface. This body may be an imbrication of the suture located in basement rocks.