The Aerogeophysical Project Serra do Mar Sul in the region of the Cunhaporanga Granitic Complex, Paraná, Southern Brazil: analysis of the gamma-ray spectrometric survey

Abstract

This paper analyses sprectrometric data of the Aerogeophysical Project Serra do Mar Sul (APSMS) in the Meso to Neoproterozoic basement of eastern Parana state, southern Brazil. Three main lithostratigraphic units are found, elongated N30-40E. The easternmost is the Tres Corregos Granitic Complex (TCGC), constituted by calc-alkaline granites and their mega-enclaves. The central unit is the low-grade metamorphic Itaiacoca Group. The western strip is occupied by the mostly calc-alkaline Cunhaporanga Granitic Complex (CGC), also with large enclaves. Further west, the molassic volcano-sedimentary Eopaleozoic Castro Group, deposited in a graben, overlies unconformably the CGC. The Devonian sandstone Furnas Formation, to the west, is the main unit of the Parana Basin in this region. The Cretaceous Banhadao alkaline massif (8 km2) intrudes the TCGC. The heavily weathered central-northern area of the CGC is in part covered by the alluvial deposits of the Iapo drainage basin. Data were corrected with a cosine directional filter (degree 6), and presented as cps (counts per second). U and K give answers that may be spurious, not always correlated with the geology. Most CGC intrusions present rather high Th-U, lower total (TC) and very low K counts, as opposed to the values found in the TCGC. High TC are found in some of the more evolved plutons within the CGC (e.g., the A-type Serra do Carambei Granite). The TCGC granites can be divided into two radiometric domains, one adjacent to the Itaiacoca belt and another to the E-SE (visible in TC and K counts), corresponding to the Sao Sebastiao Granite. The mega-enclaves show lower counts in all channels than the surrounding granites. The Itaiacoca belt is marked in TC and U-Th maps by low to medium counts. The Castro Group shows a complex pattern controlled by lithology. The Furnas sediments show low to medium responses (TC map). The Iapo river deposits stand out clearly by very low counts (TC, U, Th) against the CGC rocks.