Connecting the late Neoproterozoic flysch sedimentation in the Gariep Belt (Namibia) with its potential source region in southern Dom Feliciano Belt (Uruguay) – a U-Pb detrital and protolith zircon study.

Abstract

The Dom Feliciano Belt in Uruguay represents a counterpart of the Gariep Belt in Namibia and these two belts are presently considered as relics of one orogen split by the Atlantic Ocean. In this study, two presumed flysch samples from the Marmora Terrane of the Gariep Belt in Namibia, and five samples from potential source areas in the Nico Perez Terrane of the Dom Feliciano Belt in Uruguay have been dated to determine the possible source regions for the flysch sedimentation on the Namibian side of the orogenic system. Two granites from the Nico Perez Terrane show Neoproterozoic ages of c. 614 Ma, interpreted as the crystallization ages. These data are compatible with the magmatic activity found in the Dom Feliciano Belt from 634 – 564 Ma. A metavolcanic sample from the Zanja del Tigre Complex presents crystallization age of 1.45 Ga. One of the metasedimentary samples from the Nico Perez Terrane shows zircon ages with dominant Mesoproterozoic peak at ca. 1.45 Ga interpreted as an age of volcanic admixture, and minor amount of Paleoproterozoic and Archean zircon. interpreted as detrital grains. Another sample of metasedimentary rock shows only Paleoproterozoic to Archean zircon ages. The detrital zircon population is interpreted as a result of erosion of the surrounding geological units. Two presumed samples of metamorphosed flysch sediments from the Marmora Terrane present very different detrital zircon age spectra. One of the samples shows mainly Meso- and Paleoproterozoic ages, with individual Archean ages. This sample is interpreted as possibly connected with sedimentation in the rifting stage of the orogenic cycle. The second sample has a detrital zircon age spectrum that is consistent with syn-orogenic nature of flysch sedimentation, and shows several peaks at c. 650 Ma, 750 Ma, 1.0 Ga and 1.85 Ga. When comparing the zircon signature in the flysch sample with protolith ages found in the surrounding geological units (the Nico Perez Terrane, The Punta del Este Terrane, SouthAfrican sources and the Rio de la Plata Craton), it becomes clear that the flysch sediment is a result of erosion of the Punta del Este Terrane basement, which contains the only nearby source of the c. 650 Ma zircons, the c. 800-750 Ma zircons and inherited zircons dated at 1.2 – 1.0 Ga. The sample also shows the same detrital zircon pattern found by other workers in their studies of flysch sediments in the Dom Feliciano – Gariep Belt.