Provenance and geotectonic setting of the Paleoproterozoic Cerro Figurita formation (Río de la Plata Craton, Uruguay)

Abstract

The Cerro Figurita Formation (CFFm) represents a clastic sedimentation approximately 3000 m thick which underwent low greenschist metamorphic conditions. The sedimentary sequence is dominated by polymictic conglomerates and sandstones deposited in an environment of alluvial fans that evolve to marine turbidites. The geochemistry of the CFFm reveals derivation from sources with a mix composition similar to unrecycled Upper Continental Crust; alteration increases towards the top of the sequence (CIA 45–92). The contribution of mafic (probably ophiolitic) source rocks is revealed by petrography and low values of Th/Sc (0.3–1.5), Zr/Sc (6–20), Th/U (3–6) and high values of Cr/V (1.1–12.2); slightly negative Eu/Eu* anomalies (0.7–0.9) would indicate the presence of plagioclase in the source rocks. TDM ages are between 2001 and 2269 Ma, and the ƒSm/Nd values along with the relationship between εNd(t) andTh/Sc ratio indicate a provenance from an andesitic arc component. Detrital zircon age patterns are dominated by 2160, 2163 and 2177 Ma peaks, with the youngest zircon showing an age of 2112 ± 21 Ma, confirming a provenance from the Florida central granitic gneiss belt (FB). It is noteworthy the presence of subordinate populations of detrital zircon grains with ages of 2772, 2935 and 3222 Ma, indicating the presence of an inherited felsic source of Archean age, not yet detected in the Piedra Alta Terrane (PAT), and probably located within the Nico Pérez Terrane. A multi-approach to provenance analyses integrating geochemistry, petrography, U–Pb zircon ages, and Nd isotopes indicate ongoing active tectonism during the Orosirian in the PAT, whereas a retroarc foreland basin geotectonic setting is suggested for the CFFm deposition.