The use of pseudosections in metamorphic petrology: Basic concepts and applications, with emphasis on pelites

Abstract

The use of pseudosections in Metamorphic Petrology publications has become more common in the last 20 years due to a variety of factors, such as the advance of mineral chemistry analysis techniques using electron microprobe and laser ablation coupled with an inductively coupled plasma mass spectrometry; refinement in the treatment of isotopic data from accessory phases, such as monazite and zircon; and, mainly, improvements in software used for pseudosection calculation. Each year new updates of such software are released, but basic bibliography that contemplates the theory and practice of pseudosection calculation is rare, especially in Portuguese. This contribution aims to synthesize these aspects, which are necessary for those who wish to delve into Metamorphic Petrology. Here we present some basic principles of phase diagrams in general, and pseudosections in particular, and discuss the first steps for the construction of pseudosections. We also consider topological aspects of pseudosections in different chemical systems to exemplify the differences and similarities that occur.