Aplicação de litogeoquímica, isótopos de Sm-Nd e Sr e datação U-Pb de zircão detrítico para estudos de proveniência dos sedimentos aluviais da Bacia de Resende

Abstract

The Resende Basin is a halfgraben with a north tectonic border and about 240 km2 of area and 45 km in length on its NE-SW axis located in South-eastern Brazil. The thickness of the sedimentary filling reaches about 500 m and its registration comprises, at the base, Paleocene deposits of the Ribeirão dos Quatis Formation (pre- or syn- rifting tectonics fluvial system) underpinned by the syn-rift I sedimentary successions of the Resende Formation (braided-fluvial system with associated marginal alluvial fans). In the Oligocene, syn-rift II successions of the Pinheiral Formation (braided-fluvial system) were deposited. The Miocene deposits of the Floriano Formation (meandering fluvial system) mark the post-rift period of the basin. The present work intends to contribute to the knowledge of the evolution of the Resende Basin from studies of sedimentary provenance based on whole-rock geochemical analysis, whole-rock of Sm-Nd and Sr isotope analysis and U-Pb detrital zircon dating. Samples correspond to fluvial mudstones and sandstones and sediments from alluvial fans. The basement of the Resende Basin consists of Proterozoic rocks from the Ribeira Belt and Cretaceous alkaline rocks from the Itatiaia and Morro Redondo massifs. Both mudstones and sandstones of the Resende Formation have similar chemical signatures of trace and rare earth elements, as well as similar Sm-Nd and Sr isotopes signatures, whose variations are easily explained by differences in provenance due to different source areas and/or degrees of mixture of sources. There is a strong control of elements such as Rb and Ba, which can be associated with the presence of low-altered K-feldspars. Enrichments of Zr, Hf, Y and considerable variations in the values of the sum of rare earth elements, especially in mudstones, indicate the addition of heavy minerals (zircon and monazite). Mudstones and sandstones in the Resende Basin present values of εNd(40 Ma) and ratios of 87Sr/86Sr(40 Ma), respectively, between -4 and -21 and between 0.70603 and 0.80934. Sediments from alluvial fans have isotopic signatures like their adjacent basements, the Itatiaia fan with the Itatiaia Massif and the Penedo fan with Proterozoic rocks. Samples with εNd(40 Ma) > -10 and TDM < 1.25 Ga have a contribution of less radiogenic Cretaceous material, while samples with εNd(40 Ma) < -10 and TDM > 1.25 Ga may have or not Cretaceous contribution, revealed by the presence of Cretaceous zircons in samples with more radiogenic isotopic signatures. There is a limit on the proportion of less radiogenic content needed to interfere with Sm-Nd signatures. The Cretaceous content reflected in the isotopic signatures and in detrital zircon ages is more expressive in the westernmost portions of the Resende Structural High, Penedo Depocenter, when compared to the sediments deposited further east, Porto Real Depocenter. The content of Cretaceous zircons is also expressive in the easternmost portions of the basin, Quatis Depocenter. Probably the Resende Structural High already existed and compartmentalized the basin in two depocenters, blocking part of the sediments from the Itatiaia Massif brought from W-E direction channels to the easternmost portions of the basin. The results point to an expressive control of the basement at south-southwest in the supply of debris during the syn-rift filling