Unraveling the tectonic evolution of a Neoproterozoic–Cambrian active margin in the Ribeira Orogen (Se Brazil): U–Pb and Lu–Hf provenance data

Abstract

The Neoproterozoic–Ordovician Central Ribeira Orogen (southeastern portion), in SE Brazil, presents two contrasting tectonic domains in its southern portion: (a) the arc domain constituted of Neoproterozoic to Paleozoic magmatic rocks and low P-high T metamorphic para (São Fidelis Group)- and ortho-derived units (in Oriental Terrane); and (b) the basement domain, constituted of a Paleoproterozoic and Neoproterozoic medium P-high T metamorphic para (Palmital–Búzios succession)- and ortho-derived units (in Cabo Frio Tectonic Domain). Our work focuses on paraderived rocks sequences from both domains. The provenance analysis using U–Pb and Lu–Hf in zircon grains is presented here as an effective tool to unravel the paleogeography and nature of the pre-collisional sedimentary basins. We performed 505 analyses (U–Pb) on detrital zircon grains and some metamorphic overgrowths from six paragneiss samples. Besides, 141 analyses (Lu–Hf) in six samples only on the detrital zircon grains domains. All samples present a main peak from Neoproterozoic sources (750–570Ma) and the other minor peak in the Stenian/Tonian periods (1200–850Ma), this indicate an orogenic contribution for this basin. Scarce register from the Mesoproterozoic and two peaks in the Archean/Paleoproterozoic (2.6 and 1.9Ga) are recognized as a contribution from an ancient continent. The Lu–Hf data reveals a juvenile source for the detrital zircon grains from Buzios succession while Palmital and São Fidelis Group units show a main crustal signature for their detrital zircon population. Based on the U–Pb and Lu–Hf data presented here, plus petrological data, geological correlations, and compilation of data from literature, we propose a tectonic model for the origin of para-derived rocks from the eastern part of the Ribeira Orogen. In at least two stages, starting with an extensional environment of ca. 600Ma in a back-arc basin (Buzios succession deposition) and continuing as an active margin between 570 and 550Ma in the fore-arc and prism basin (São Fidelis Group and Palmital succession).