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|Type:||Artigo de periódico|
|Title:||Reconnaissance U-Pb geochronology of Precambrian quartzites from the Caldeirao belt and their basement, NE Sao Francisco Craton, Bahia, Brazil: implications for the early evolution of the Paleoproterozoic Itabuna-Salvador-Curaca orogen|
|Abstract:||Subvertical quartzites and pelitic schists crop out in structural conformity with gneisses and migmatites in the Precambrian Caldeir (a) over tildeo Belt, northeastern S (a) over tildeo Francisco Craton. Their deformation and metamorphic history are related to the evolution of the Paleoproterozoic Itabuna-Salvador-Curaca orogen. The Caldeir (a) over tildeo Belt is situated at the western edge of the Archaean Uaua Block. Zircons from one quartzite have sensitive high resolution ion microprobe (SHRIMP) Pb-207/Pb-206 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 Caldeir (a) over tildeo Belt orthogneiss yield a SHRIMP Pb-207/Pb-206 age of 3152 Ma, whereas two gneisses from the Uaua Block yield conventional U-Pb ages of 2933 and 2991 Ma. These ages indicate that rocks from the Uaua Block, or from areas of similar ages, may have supplied sediments to the basin that eventually formed the Caldeir (a) over tildeo Belt quartzites and pelitic schists. Our results support the suggestion that the Itabuna-Salvador-Curaca orogen evolved through deposition of sediments on a passive-type continental margin, followed by accretion of arc sequences and continent-continent collision. (C) 2002 Elsevier Science Ltd. All rights reserved.|
|Editor:||Pergamon-elsevier Science Ltd|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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