Late Neoproterozoic P-T-t paths of syn- and post-collisional metamorphism in the Paranaguá Terrane, Ribeira Belt (Brazil): implications for West Gondwana assembly

Abstract

ABSTRACT Phase diagram modelling and U-Pb monazite ages reveal a clockwise Pressure-Temperature-time metamorphic evolution in the Paranaguá Terrane (Ribeira Belt – SE Brazil) and characterized important tectonic events. Comparisons of our dataset with the Dom Feliciano and Kaoko belts indicate a contrasting metamorphic evolution of South American and African units during West Gondwana assembly. The Paranaguá Terrane is considered an arc-related unit formed during the western Gondwana accretion, comprising Paleoproterozoic basement inliers, metasedimentary rocks and late Neoproterozoic granites. Metapelites mineral assemblages and chemistry combined with isotopic data indicate three tectonometamorphic stages for the terrane. M1 (640–610 Ma) is associated with collisional processes that resulted in a greenschist to lower amphibolite facies regional metamorphism (540–580°C and ~6-8 kbar). The progression of the metamorphism followed a decompression path of c. 2–4 kbars and reached P-T conditions of ~725°C at ~5 kbars (M2 – 610-580 Ma). M2 is associated with post-collisional processes related to slab-break off and partial exhumation of deeply buried sequences. Metapelites low-temperature retrograde conditions define a late M3 (540–500 Ma) metamorphic event. Our results demonstrate the similarities and differences of the Paranaguá-Dom Feliciano-Kaoko orogenic system. The metamorphic evolution of the Paranaguá Terrane and Northern Dom Feliciano Belt exhibits a geothermal gradient controlled by broad magmatic activity and post-collisional processes. In contrast, their suggested African counterpart (Kaoko Belt) shows a Barrovian metamorphic trend. This dataset permitted a refined time-space evolution of these southwest Gondwana units.