Origin of the Ediacaran Porongos Group, Dom Feliciano Belt, southern Brazilian Shield, with emphasis on whole rock and detrital zircon geochemistry and U-Pb, Lu-Hf isotopes

摘要

The Porongos Group is the major component of a fold and thrust belt located in the central portion of the Dom Feliciano Belt in the Sul-Riograndense Shield, Brazil. In this paper, the variations in composition of sediments and the depositional time are presented. Major and trace elements indicate that Porongos Group is composed mostly of immature sediments derived from intermediate felsic sources with minor contribution from mature recycled sources. U-Pb SHRIMP ages for a chlorite schist (sample 300) exhibit a proeminent population of 570-800 Ma, subordinate population of 1800-2250 Ma and minor population of 1200 Ma, whereas for a schist (sample 198) the main population is 1050-1500 and minor populations are 2040-2300 and 580-800 Ma. The epsilon Hf values of Neoproterozoic grains indicate variable degrees of crustal reworking (epsilon Hf = -18 to -4) with three main T-DM model ages (2.2, 1.8, 1.5 Ga). The Paleoproterozoic grains include a few Archean (3.2-2.5 Ga) T-DM ages. The trace elements of all analyzed detrital zircon grains reflect continental crust origin. According to the data set, the sediments of the Porongos Group were derived from locally eroded granitic rocks of the Dom Feliciano Belt and from the uplifted Paleoproterozoic basement (La Plata Craton). Further analytical signal and total magnetic field maps delimit regionally the shape and extension of the Porongos fold and thrust belt and includes the Capane region. We conclude that the duration of Porongos Group basin filling probably lasted from 650 to 570 Ma in a foreland tectonic setting of the Dom Feliciano Belt. (C) 2015 Elsevier Ltd. All rights reserved.