Journal of South American Earth Sciences ( IF 1.704 ) Pub Date : 2020-01-02 , DOI: 10.1016/j.jsames.2019.102495 Hans-Joachim Massonne
The comments to the publication by de Oliviera Chaves et al. (2019) refer to the derivation of eclogite-facies conditions for micaschist from the Paleoproterozoic Itaguara Sequence in the southern São Francisco Craton in Brazil. These authors derived peak pressures of 18.5 kbar at 626 °C for this rock using phengite geobarometry. A scrutiny of their analytical data and the applied geothermobarometry led to the conclusion that these pressures were at most 13–14 kbar and possibly even below 10 kbar. Temperatures did not exceed about 600 °C. Thus, melting of the studied micaschist is unlikely. A subduction-related process in the Paleoproterozoic to form the Itaguara Sequence, as suggested by de Oliviera Chaves et al. (2019), must be called in question.