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IDADES U-Th-Pb E U-Pb EM MONAZITA DE ORTOGNAISSE DO COMPLEXO JAMARI, ÁREA DO DEPÓSITO DE ESTANHO DE BOM FUTURO (RO)

2006; Sociedade Brasileira de Geologia; Volume: 36; Issue: 1 Linguagem: Inglês

10.25249/0375-7536.200636s17176

2177-4382

Valmir da Silva Souza, Luciana Miyahara Teixeira, Elton Luiz Dantas, Nilson Francisquini Botelho, Jorge Henrique Laux,

Iron oxide chemistry and applications

Electron microprobe U-Th-Pb dating of monazite is applied to the geothermobarometric study of metamorphic terrains and provides important results, compatible with absolute geochronological methods. This paper compares the analytic results obtained by eletron microprobe U-Th-Pb with isotopic dilution U-Pb in monazite from orthogneiss of the Paleoproterozoic Jamari Complex, in Rondônia State, Brazil. The monazite grains are rounded, clean and not zoned, ranging from 0,5 to 1,5 mm, characterizing a monogenetic Ce-monazite. The Pb-Th* cationic diagram analysis revealed an age of 1327 ± 20 Ma and the U-Pb concordia diagram yielded an age of 1331±0,98 Ma. These values, in spite of the lower precision of the method, reinforce the applicability ofthe U-Th-Pb eletron microprobe analysis in geochronological investigations. The obtained ages are interpreted as records of a tectonometamorphic event that affected the basement rocks in central Rondônia during the Rondonian-San Ignácio orogeny.