GEOTHERMOMETRY OF THE METAPELITES OF THE INTERMEDIATE UNITS OF THE PASSOS NAPPE (MG)

Abstract

In the São Sebastião do Paraíso region (MG), medium to high-grade metamorphic metasedimentary rocks of the Passos Nappe are laterally arranged in a short east-west route, marking an inverted metamorphic gradient towards the top, with the presence of high-pressure granulite and eclogite, and are interpreted as continuous. However, this association may indicate the presence of a discontinuity, raising the possibility of the nappe having more than one allochthonous unit. The Zr in rutile geothermometer indicates temperatures between 638 ± 18ºC and 667 ± 11ºC in rocks positioned tectonostratigraphically below the retroeclogite occurrences, and temperatures between 665 ± 12ºC and 709 ± 9ºC for rocks above. The metapelitic schists show mineralogical, textural, modal, and temperature similarities, indicating a medium-grade metamorphism. However, the top of Unit G exhibits a higher-grade metamorphic paragenesis, as proven by the higher temperature values obtained. The increasing thermal gradient along the studied units confirms the presence of an inverted metamorphic gradient for the nappe. However, no temperature jump was observed, indicating that discontinuities between these units of the Passos Nappe are unlikely.