U-Pb zircon provenance of metamorphosed clastic sediments in the Brusque Metamorphic Complex, Dom Feliciano Belt, southeastern Brazil

Abstract

The Brusque Metamorphic Complex is situated in the northern part of the Dom Feliciano Belt in the state of Santa Catarina, southeastern Brazil. The complex is composed of Neoproterozoic sequences of volcanic and sedimentary rocks, which were folded and metamorphosed at greenschist to low-amphibolite facies conditions. U-Pb dating of detrital zircon grains in five samples of clastic metasedimentary rocks in the Brusque Metamorphic Complex has revealed a mixed source for the detritus in the sedimentary succession. Two quartzite samples, suggested as representing the lower part of the succession related to early Neoproterozoic rifting, show detrital zircon ages consistent with erosion of the Paleoproterozoic-Archean basement of the Río de la Plata and Congo cratons, as well as erosion of an inferred Mesoproterozoic volcano-sedimentary cover of these cratonic units. Two other quartzite samples, suggested as representing the upper part of the succession, yielded predominantly Paleoproterozoic zircon ages with affinity to the Congo and Río de la Plata cratons, as well as the Luís Alves Microplate. The suppression of Mesoproterozoic detrital zircons towards higher stratigraphic level in the sedimentary succession of the Brusque Metamorphic Complex is suggested to reflect gradual erosion of the Mesoproterozoic cover. A phyllite sample, containing mostly late Neoproterozoic and only small number of Paleoproterozoic zircons, is interpreted as being a part of the adjacent Itajaí Basin molasse sediments rather than the Brusque Metamorphic Complex. While the Neoproterozoic zircons in this sample are suggested as derived from the Coastal-Punta del Este Terrane and the Florianópolis Batholith, the Paleoproterozoic zircons probably represent second-cycle grains derived from erosion of the Brusque Metamorphic Complex itself. Detrital zircon grains in the metasedimentary succession of the Central Kaoko Zone in the Kaoko Belt in northern Namibia, at the opposite side of the South Atlantic Ocean, reveal very similar age signals as those observed in the studied samples of the Brusque Metamorphic Complex. Such similarity suggests an origin in a common sedimentary basin, where the Brusque Metamorphic Complex represented a western margin and the Central Kaoko Zone an eastern margin of a developing early Neoproterozoic rift system.