Detrital Zircon U-Pb Age Data, and Precambrian Provenance of the Paleozoic Guaritas Formation, Southern Brazilian Shield

Ion microprobe age investigation of 73 detrital zircon crystals contained in a sandstone sample from the Paleozoic Guaritas Formation, southern Brazil, provides insights into the tectonic evolution of the southern Brazilian shield. The zircon U-Pb ages reflect three major orogenic cycles-Neoarchean, Paleoproterozoic (2.26-2.00 Ga), and Neoproterozoic (880-535 Ma), including both juvenile and crustal reworking events. Zircon age peaks indicate that each orogeny had several pulses of granite injection. We conclude that the zircon crystals were derived from rocks from the southern Brazilian shield; no African connection is required to explain the age distribution. The shield was part of supercontinent Columbia, because few ages are observed between 2.0 and 0.9 Ga as a consequence of lack of orogenic activity. Final cratonization of the southern Brazilian shield occurred at 560 Ma, but some granitic activity extended to 535 Ma. Thus, detrital zircon ages provide a reliable proxy for the chronostratigraphy and orogenic history of extensive tracts of the southern Brazilian shield.