Reconnaissance U–Pb geochronology of Precambrian quartzites from the Caldeirão belt and their basement, NE São Francisco Craton, Bahia, Brazil: implications for the early evolution of the Paleoproterozoic Itabuna–Salvador–Curaçá orogen

Subvertical quartzites and pelitic schists crop out in structural conformity with gneisses and migmatites in the Precambrian Caldeirão Belt, northeastern São Francisco Craton. Their deformation and metamorphic history are related to the evolution of the Paleoproterozoic Itabuna–Salvador–Curaçá orogen. The Caldeirão Belt is situated at the western edge of the Archaean Uauá Block. Zircons from one quartzite have sensitive high resolution ion microprobe (SHRIMP) 207Pb/206Pb ages between 2687 and 3209 Ma in their preserved cores and about 2076 Ma at their rims. The first age-distribution defines ages of the source rocks to the quartzites, whereas the second characterizes the timing of regional high-grade metamorphism. The deposition of the quartzites and associated pelitic schists is bracketed between 2076 and 2687 Ma. Zircons from one Caldeirão Belt orthogneiss yield a SHRIMP 207Pb/206Pb age of 3152 Ma, whereas two gneisses from the Uauá Block yield conventional U–Pb ages of 2933 and 2991 Ma. These ages indicate that rocks from the Uauá Block, or from areas of similar ages, may have supplied sediments to the basin that eventually formed the Caldeirão Belt quartzites and pelitic schists. Our results support the suggestion that the Itabuna–Salvador–Curaçá orogen evolved through deposition of sediments on a passive-type continental margin, followed by accretion of arc sequences and continent–continent collision.