Produção Nacional
TITANITA-BIOTITA GRANITOS DO BAIXO RIO UAUPÉS, PROVÍNCIA RIO NEGRO, AMAZONAS. PARTE I: GEOLOGIA, PETROGRAFIA E GEOCRONOLOGIA
1992; Sociedade Brasileira de Geologia; Volume: 22; Issue: 1 Linguagem: Inglês
10.5327/rbg.v22i2.390
ISSN2317-4889
AutoresRoberto Dall’Agnol, Moacir José Buenano Macambira,
Tópico(s)Paleontology and Stratigraphy of Fossils
ResumoTitanite biotite granitoids and gneisses are dominant rocks in the Rio Negro Province (RNP), NW Amazonas State, Brazil. Batholithic bodies, composed of these rocks, outcrop in the Low Uaupes River area. In this region, little deformed titanite-biotite monzogranites (TBMG) are the major rock type. The granites of this area are here named Rio Uaupes Granite (RUG). Their principal petrographic characteristics are: relatively low modal quartz; significantly high anorthite contents of plagioclase (cores of calcic andesine); extremely high average modal percentages oftitanite + opaques (magnetite + ilmenite ± pyrite) + apatite (4.7% in the TBMG). Magnetic susceptibility measured on hand samples is systematically high in the TBMG (395.3 to 189.7 x 10 -4 SI), decreasing in the hololeucocratic fades (108.9 to 21.2 x 10 -4 SI). Therefore, the RUG are classified as magnetite series granites. Rb-Sr whole rock isochronic dating of RUG gives an age of 1459±32 Mawith 87 Sr/ 86 Sr) initial ratio of 0.70631 ± 0.00117, suggesting that the RUG magma formed directily from crustal rocks or was derived from mantle sources but suffered strong crustal contamination. Concerning the tectonic evolution of RNP, a continental collision model is coherent with the available information, but more geological and structural data are necessary to demonstrate this hypothesis.
Referência(s)