Abstract
Abstract Salinas Formation occurs in a large region of the Northern Aracuai orogen, Southeastern Brazil. It includes turbiditic wackes (> 10% matrix) to arenites (< 10% matrix), pelites and clast-supported conglomerates, metamorphosed from the biotite zone of the greenschist facies to the sillimanite zone of the amphibolite facies. Salinas Formation lies unconformably on the top of or in tectonic contact with the Macaubas Group, and hosts Cambrian granitic intrusions dated between 540 and 500 Ma. Aiming to unravel sediment provenances for the Salinas basin, we present a detailed lithochemical (45 samples) study on low-grade rocks preserved from the regional deformation, which are found in the type area of the Salinas Formation. In addition, we compare them with deformed and more metamorphic rocks of similar composition but located in other basin sectors. The lithochemical data indicate limited chemical weathering in the sediment sources, good correlations with the mineralogical compositions in respect to the variable amounts of metamorphic minerals typical of pelitic (micas, garnet, and other peraluminous silicates) and psammitic (feldspars, quartz) fractions. The main provenances of sedimentary protoliths are clearly related to continental magmatic arc and active continental margin environments. U-Pb (SHRIMP) analyses performed on zircon grains from clasts of intermediate to felsic volcanic rocks, extracted from a clast-supported metaconglomerate, yield concordant zircon Pb206 /U238 ages from ca. 579 Ma to ca. 697 Ma, with most of the ages in the interval of 587 to 630 Ma. This indicates that the main primary sediment source is the Rio Doce magmatic arc (630-580 Ma), in very good agreement with the arc-related lithochemical signature. Eleven zircon crystals yield a Concordia age of 620 ± 10 Ma, representing an important Ediacaran volcanic episode in the tectonic evolution of the Aracuai orogen.
Highlights
There are useful lithochemical approaches to investigate genetic attributes and tectonic environments of metasedimentary rocks, processes like weathering, diagenesis, and metamorphism may considerably change the composition of sedimentary materials
Fourteen samples are from wackes metamorphosed in the very low-grade biotite zone, but preserved from orogenic deformation, collected in the type area of Salinas Formation, and 31 samples are from deformed and more metamorphic lithotypes collected in the southern sector of the Salinas basin (Fig. 1)
Petrographic, geochronological and lithochemical studies, comparing the results from the samples collected in the type area of Salinas Formation, located in the surroundings of Salinas city, with the samples collected along the Minas Novas corridor (Fig. 1)
Summary
There are useful lithochemical approaches to investigate genetic attributes and tectonic environments of metasedimentary rocks, processes like weathering, diagenesis, and metamorphism may considerably change the composition of sedimentary materials (cf. Bhatia 1985, Bhatia & Crook 1986, Rosen 1992, McLennan et al 1993, Slack & Höy, 2000, Augustsson & Bahlburg 2008, Verma & Armstrong-Altrin 2013). In the semi-arid Jequitinhonha river valley, Northern Araçuaí orogen (Fig. 1), the Salinas Formation provides several good exposures of non-weathered metasedimentary rocks They vary from very low-grade metasiliciclastic rocks (wacke, arenite, and pelite), which were preserved from the regional orogenic deformation, to their deformed equivalents metamorphosed up to the sillimanite zone of the amphibolite facies (Pedrosa-Soares 1995, Pedrosa-Soares & Leonardos 1996, Pedrosa-Soares et al 2001, 2008, Lima et al 2002, Santos et al 2009, Peixoto et al 2017). The results disclose correlations between non-deformed and deformed lithotypes and reinforce the useful application of the lithochemical approach to study similar rocks in other orogenic belts They corroborate the orogenic nature of the Salinas basin (Lima et al 2002, Santos et al 2009, Peixoto et al 2015, Costa et al 2018). This definitely links it with sediment sources in the Rio Doce magmatic arc (Tedeschi et al 2016, Novo et al 2018)
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