U–Pb SHRIMP ages for the Cerro Bori Orthogneisses, Dom Feliciano Belt in Uruguay: Evidences of a ~800Ma magmatic and ~650Ma metamorphic event

Abstract

Neoproterozoic ages of magmatic and metamorphic events were obtained from in situ SHRIMP analysis of zircons from the Cerro Bori Orthogneisses, eastern domain of the Dom Feliciano Belt in Uruguay. Detailed textural analysis of zircons and their ages revealed a much more complex evolutionary history for these rocks than previously thought. Twelve samples were studied and revealed crystallization ages between 802 and 767 Ma, determined from the typical magmatic oscillatory zoning domains from the zircons. These magmatic domains are cut by recrystallization fronts and mantled by metamorphic rims. The recrystallization fronts and rims are interpreted to be related to a high grade metamorphic event with a maximum age of ~676 Ma, whereas the rims considered to be related to partial melting are 654 ± 3 Ma old. The new magmatic ages demand a reinterpretation of the evolutionary history of this crustal segment, which is one of the few occurrences of the early Brasiliano Orogenic Cycle rocks in South Brazil and Uruguay. The metamorphic/partial melting event is inferred to be related to crustal thickening as a consequence of collision of the Rio de la Plata with the Congo and Kalahari cratons, during the amalgamation of West Gondwana.