Abstract
A regional petrologic study based on mineral parageneses and mineral chemistry in metapelitic rocks of the Serido Foldbelt in Northeastem Brazil was undertaken. Two stages of deformation are preserved in these rocks. The first one (F n ) produced isoclinal recumbent folds trending NNE, whereas symmetric to assymetric open to tight folds trending N1OE resulted from the second event(F n +2). Pressures and temperatures using garnet-plagioclase and garnet-biotite exchange reactions indicate a metamorphic field gradient of 30o-40oC/km during- the second stage of deformation, The metamorphic grade in general increases from west to east, reaching a maximum in the central part of the studied area, Partial (garnet) to total (biotite) chemical reequilibration of the phases crystallized during the first deformation occurred at the time of the second event. Calibrated equilibria involving hydrous phases indicate that the activity of H 2 0 during the second metamorphism was close to 0.5.
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