Contributions of gamma‐ray spectrometry to terrestrial impact crater studies: The example of Serra da Cangalha, northeastern Brazil

Abstract

Several geophysical methods have been used for decades for the identification and exploration of impact craters. Most of them are based on seismic, potential fields and electrical data, focusing on exploration of anomalies caused by changes in physical properties or by structures associated with the formation of the crater. Gamma‐ray spectrometry is usually not mentioned among the geophysical methods employed in crater studies, although it is known that impact cratering processes cause a number of physical/chemical changes in the country rocks. These changes include the remobilization of hydrothermal fluids which directly modify the composition of target rocks and, subsidiarily, of soils related to these rocks. Therefore, the distribution of radioactive elementsK, Th and Uhas the potential to map such modifications. We present the analysis of gamma‐ray signatures at the Serra da Cangalha impact structure, located in northeastern Brazil, using methods for enhancingKanomalies and also the overall gamma‐ray signatures. These results provide valuable information on the distinct zones within the crater and might contribute to the understanding of hydrothermal enrichment processes produced as a result of the impact event.

Geology and impact features of Riachão structure, northern Brazil

“…Riachão has an outstanding gamma‐ray signature, characterized by a “bull's eye” pattern similar to the one previously found for the nearby Serra da Cangalha impact structure (Vasconcelos et al. ). Gravity and magnetic signatures associated with the impact structure are positive.…”

Mineralogy, provenance, and diagenesis of a potassic basaltic sandstone on Mars: CheMin X‐ray diffraction of the Windjana sample (Kimberley area, Gale Crater)

“…This would suggest that the trachyte source was ultrapotassic, which is perhaps more characteristic of metasomatic rocks including pseudo‐trachytes [ Le Bas , ]. Thus, we cannot exclude a metasomatic source; and it is an interesting possibility that hydrothermal effects around Martian impact craters could include widespread potassic metasomatism [e.g., Currie , ; Pesonen et al , ; Pirajno , , ; Vasconcelos et al , ].…”

Geological and geophysical studies of the Agoudal impact structure (Central High Atlas, Morocco): New evidence for crater size and age

“…They are identified and confirmed by the presence of diagnostic criteria observed in the field at the mesoscale (SCs, see Baratoux and Reimold 2016) and/or in the laboratory at the microscopic scale (e.g., shocked quartz with planar deformation features; French and Koeberl 2010). They are also generally associated with geophysical signatures (which are not diagnostic of meteoritic impact) such as circular gravity, magnetic, electric conductivity, or radiometric anomalies (Pilkington and Grieve 1992;Boamah and Koeberl 2002;Vasconscelos et al 2012;Baratoux et al 2019). Geophysical analyses are also useful to explore for possible buried impact structures, which are then confirmed by the documentation of shock effects from samples obtained from drill cores (e.g., Kenkmann et al 2015).…”

“…They are also generally associated with geophysical signatures (which are not diagnostic of meteoritic impact) such as circular gravity, magnetic, electric conductivity, or radiometric anomalies (Pilkington and Grieve ; Boamah and Koeberl ; Vasconscelos et al. ; Baratoux et al. ).…”