Long-lived high- to ultrahigh-temperature metamorphism constrained by reconstructing P-T-(t) paths of metasedimentary rocks: Example from the Neoproterozoic Guaxupé Nappe, Southernmost Brasília Orogen, SE Brazil

Worldwide occurrences of metamorphic rocks that underwent ultrahigh-temperature metamorphism (T>900 °C) demonstrate that the continental crust has experienced heat anomalies that drastically disrupted its thermal state, mostly during mountain-building events throughout space and time. In few cases, it is debated whether this type of metamorphism is related to local heat anomalies or to progressive regional metamorphism. An example of this occurs in the Guaxupé Nappe, southernmost Brasília Orogen (SE Brazil), formed in an arc to continental collision setting during the Neoproterozoic amalgamation of Western Gondwana. In this contribution, we reconstruct the metamorphic P–T–(t) paths of two metasedimentary migmatites from different crustal depths of the Guaxupé Nappe to constrain the conditions, extent and timing of high-grade metamorphism, evaluate the presence of a metamorphic gradient and explore the potential heat sources responsible for the extreme metamorphic conditions in the area. The garnet diatexite (#OS14b), collected from intermediate crustal levels, exhibits peak P–T conditions of ~925–1040 °C and 8.5–11 kbar (depths of ~28-37 km and T/P ratio of ~1088-945 °C/GPa), and retrograde conditions of ~680–755 °C and 5.5–6.5 kbar (depths of ~18-22 km). The garnet-cordierite metatexite (#RSJ09), collected from upper crustal levels, yields peak P–T conditions of ~835–910 °C and 6–7 kbar (depths of ~20-23 km and T/P ratio of ~1392-1300 °C/GPa), and retrograde conditions of ~665–815 °C and