Magnetic and radiometric signatures of alkaline rocks and gabbros from the Ponta Grossa Arch, southeastern Paraná Basin, Brazil

Abstract

We present airborne magnetic and radiometric characteristics of some igneous suites from the Ponta Grossa Arch Alkaline Province (southern Brazil), namely the Bairro da Cruz, Banhadão, Barra do Itapirapuã, Mato Preto and Tunas complexes, Barra do Teixeira Phonolite, Itapirapuã Nepheline syenite, and José Fernandes Gabbro. We applied magnetic susceptibility 3D inversions using the total magnetic anomaly data together with its analytic signal of the vertical integral and the vertical integral of the analytic signal for the Bairro da Cruz, José Fernandes, and Tunas intrusions. Gamma-ray spectrometric methods involved analyses of basic, ternary, and ratio maps, thorium-normalized parameters, and radioelement concentrations at sampled data points. Stacked profiles from geophysical data were generated for each rock. The Bairro da Cruz, José Fernandes, and Tunas intrusions are associated with dipolar anomalies with normal polarity whereas their inversions show low magnetic susceptibility values. Gamma-ray spectrometric results allowed us to verify that all complexes are enriched mainly in eTh. Carbonatite bodies showed the highest contents of eTh and eU. Our findings are consistent with geophysical responses of alkaline bodies and impact the understanding of geophysical signatures, especially radiometric ones, of alkaline provinces in Brazil.

KEYWORDS:
airborne gamma-ray spectrometry; aeromagnetics; Ponta Grossa Arch Alkaline Province; alkaline rocks; carbonatites