Airborne geophysical data processing to isolate magnetic anomalies associated to dikes

• Grant number: 19/20172-7
• Support type: Regular Research Grants
• Duration: December 01, 2019 - November 30, 2021
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geophysics
• Principal Investigator: Carlos Alberto Mendonça
• Grantee: Carlos Alberto Mendonça
• Home Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Assoc. researchers: Ulrich Ofterdinger ; William Pareschi Soares

Abstract

This research proposal will develop a procedure to deal with the magnetic interference generated by basalt covers that usually obscure the identification of underlying dikes or dike swarms. The magnetic patterns generated by the interference of anomalies from the basalt cover and underlying dikes are not trivial, since the magnetization of the basalt layers at the top tends to be very irregular, their contribution obscuring the lower amplitude anomalies from the underlying dikes. Little is known about the positioning of dikes in this scenario, their actual distribution under the basalt trap, what of them reach the sedimentary basin or intersect different levels in the basin. At the present stage, the positioning of these intrusive structures is not possible using aeromagnetic data alone, either by applying data processing techniques or data inversion approaches. The procedure here proposed consists in applying a directional rejection filter (directional cosine in preliminary simulations) as an approximation of what is called the "bi-dimensional field annihilator". With the application of this filter, a magnetic background is obtained which, within the considered approximation, has only the contributions from three-dimensional sources. The subtraction of this background field from the original measured data isolates the contribution from the elongated sources, which in many cases represents the fields arising from dikes. Once isolated, the anomalies can be featured in profiles and subjected to 2D data inversion, for example, using the INVDIKE program developed by our research group. The parameters obtained with data inversion will be used to situate the distribution of dikes in the framework of the basalt cover. The procedure will undergo numerical simulation tests and then applied to the GSI (Geological Survey of Ireland) Tellus project and an ANP distributed data sets from the Paraná Basin, Brazil. This proposal calls for resources for computational facilities and publishing support to aid ongoing graduate projects. (AU)