Dyke positioning according to sedimentary basins markers by processing airborne magnetic data at basalt covered areas

Abstract

SUMMARY Airborne magnetics have found few applications in investigating basalt-trapped areas because anomaly interferences from deep and shallow sources prevent clear identification of subjacent dyke systems. The structural positioning of dykes is of major importance in basin studies due to their role as a heat source for maturing organic matter and plumbing capacity to feed intrusive bodies and surface lava flows. Aeromagnetic data in such a scenario can outline faults and the basin framework but faces difficulties in identifying the distribution of dykes seated at different depth levels. We present a procedure that sequentially combines conventional processing techniques to identify and retrieve the magnetic anomaly content with 2-D properties, as expected from tabular dykes with contrasting magnetic properties with respect to the background medium. The mean direction of 2-D anomalies is quantitatively evaluated by tracking the directions in which the horizontal component of the transformed anomaly mostly vanishes. The observed field is then cosine-direction filtered to retain the anomaly content along this mean direction. Once isolated, the filtered 2-D content of the anomaly is interpreted with multiple thin-sheet models to determine the dyke distribution and their respective depths to the top. The inferred depths are interpreted concerning basin stratigraphic markers to recognize dykes possibly serving as a heat source for geothermal or petroleum and gas maturation, acting as compartments to aquifer systems, or determining the location of former conduits once feeding the lava flow volcanism. The developed procedure is applied to the Ponta Grossa Dyke Swarm, along its northwestern continuation beneath the basalt-capped sedimentary sequences of the Palaeozoic Paraná Basin. The distribution of the dykes recognizes a sequence confined to the bottom Palaeozoic formations with petroleum and gas potential, a sequence intercepting the upper layers forming the Guarani aquifer system (GAS) and dykes at different depth levels within the basalt Serra Geral traps, indicative of at least two feeding events supplying the Mesozoic surface lava flows.