Aeromagnetic data analysis and physical-chemical properties of some complexes from Goiás Alkaline Province

Abstract

The Goias Alkaline Province (GAP), located on the north edge of the Parana Basin, has alkaline complexes with strong gravity and magnetic signatures. The 3D inversion of magnetic signal was performed on the aeromagnetic data. Since the intrusions present a strong remnant magnetizations as measured in the laboratory a careful analysis of this component was also realized. The sum vector of the remnant and induced components were used as a virtual induced magnetic field during the inversion process. The geometric parameters were obtained form the quantitative analysis of magnetic data using Total Gradient Direction and Analytical Signal Phase performed over magnetic signal reduced to the pole. Magnetic susceptibility and density were measured in laboratory. All those information were used as the initial model in the inversion. The results of 3D inversion show that the alkaline intrusions have roots up to 10-12 km depth. The magnetic susceptibility is distributed in almost spherical and cylindrical shapes. The possibility of spherical shapes arise the hypothesis that the GAP intrusions at the north part of the province represent magmatic chambers. The alkaline magma ascends from the lithosphere, used two main fault systems as space for emplacement. These faults systems appear in the magnetic signal analysis as linear magnetic features. Chemical analysis confirmed the alkaline and subalkaline character of the magmas. The high MgO content shows the primitive character of these intrusions but the Ba anomaly indicates a possible crustal contamination.