Provenance study of Phanerozoic rocks from the Cordillera Real of Bolivia

Abstract

U/Pb ages of detrital zircon from two samples of Ordovician sediments were determined and, based on similar published data, were compared with xenocrystal inheritance of Triassic and Oligocene granitoids of the Cordillera Real in order to better understand their genetic relationship and sources. The results show that the detrital zircon in the Ordovician sandstone and the inherited zircon cores in granitoids are statistically correlated. This correlation suggests assimilation of these sedimentary units by the felsic melts. Ages ranging from 300 to 2300 Ma are recorded in these inherited zircons. A high peak of Cambrian to late Neoproterozoic ages (500-750 Ma) is observed throughout metasedimentary units of the entire belt. Candidates for the main sources of these zircons include: Brasiliano or Pampean belts and/or an "in situ" hidden belt within the Central Andes or via recycling of detrital zircons in pre-existing sedimentary rocks. It is also possible that the sources lie below modern sedimentary covers but, at the time, formed high relief structures supplying recycled material into the Ordovician basins.