U-Pb zircon provenance of metamorphosed clastic sediments in a developing rift (Dom Feliciano Belt, Uruguay and Kaoko Belt, Namibia)
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Geochronological studies of the westernmost part of the Kaoko Belt in Namibia, the Coastal Terrane, revealed zircons with distinct Neoproterozoic ages, that are no known from other parts of this orogen and an exotic origin was thus proposed for this tectonic unit. The same temporal evolution is known for the Punta del Este Terrane, the easternmost part of the Dom Feliciano Belt in Uruguay and these units are presently considered as one tectonic domain split by the Atlantic Ocean. In this study, dating of detrital zircons from metamorphosed clastic sedimentary rocks has been done to evaluate the relationship of the Coastal Terrane - Punta del Este to the neighboring cratonic domains. In addition, two metagranitoid rocks have been dated in order to better constrain the pre- metamorphic history of the studied unit. Two quartzite samples from the metasedimentary sequence of the Punta del Este Terrane show dominance of Paleoproterozoic ages compatible with the Rio de la Plata Craton as a source region. Zircons in one of these samples also revealed ages of c. 610 Ma, which are interpreted as grains recrystallized during granulite-facies metamorphism. Two samples of metamorphosed granitoid rocks revealed magmatic events at c. 770-800 Ma and at c. 656 Ma. Sample of quartzite from tectonically lowermost Coastal Terrane shows mostly Paleo- and Mesoproterozoic ages of detrital zircons indicating the Congo Craton as a source region. One sample of metasedimentary migmatitic gneisses collected from the tectonically upper part of the Coastal Terrane shows dominance of c. 760 Ma old detrital zircons, which suggests erosion and redeposition of rifting-related magmatic rocks. Two other samples have shown almost exclusively c. 650 Ma and c. 620 Ma old zircons. As these ages are known as the age of high-grade metamorphism in the Coastal Terrane, zircons of this age are interpreted as originating from dissolution and neocrystallization, or recrystallization of older detrital zircons. The detrital zircon age groups in the studied samples are compatible with the ages known from the basement rocks of the neighboring cratonic domains. This suggests that the Coastal Terrane - Punta del Este is not an exotic unit, but probably originated in close proximity of the Congo and Rio de la Plata Cratons during Neoproterozoic rifting of the Rodinia supercontinent.