Detrital zircon U-Pb provenance analysis of Precambrian and Paleozoic strata from southwestern Brazil: Assessment of potential Grenvillian sediment input and Amazonian-Laurentian tectonic interaction

Southwest Amazonia is proposed to have collided with southeast Laurentia during the Grenville orogeny. In Laurentia, the collision produced a continental-scale late Mesoproterozoic to early Neoproterozoic clastic wedge dominated by detrital zircon (DZ) sourced from Grenvillian magmatic rocks (major Geon 11 and 10, with minor Geon 13, 12, and 9 ages: the “Great Grenvillian Sedimentation Episode”). New DZ ages in clastic units from southwestern Brazil permit testing the hypothesis that Grenvillian sediment from southeast Laurentia spilled onto western Amazonia during Rodinian assembly. Late Mesoproterozoic arenites are dominated by Geons 18, 17, 15, 14, and 13 ages sourced from Amazonia basement provinces. Two samples exhibit major Geon 12 and 11 ages with minor Geon 18–13 ages. Geon 12 and 11 correspond to a conspicuous age gap in Amazonian magmatic events. Latest Neoproterozoic samples exhibit minor Geon 13 to 9 ages interpreted to be sourced from the Rondônia-San Ignacio or Sunsás provinces of western Amazonia. Late Neoproterozoic and Devonian age spectra exhibit multiple Amazonian age modes ∼2500 to 500 Ma but with no dominant modes. The age distributions for all samples indicate a lack of Laurentian Grenville sediment influx to southwest Amazonia during Rodinian assembly and breakup. The enigmatic Geon 12 ages are interpreted to correspond to a buried Andean source or the southwestern Grenville province in Laurentia. In contrast to exposed basement in southwestern Amazonia, Andean basement clastic sequences and Pleistocene to Recent Amazon River sediments exhibit Grenville dominance of DZ ages, strikingly similar to eastern Laurentia clastic systems. The Andean Grenville dominance may be accounted for by extensive Grenvillian crust beneath the Andean clastic wedge containing a major component of Geons 12, 11 and 10 magmatic rocks, and which was not being fully exhumed until the Neoproterozoic, similar to Laurentian Grenville.