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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

10.25249/0375-7536.1992314

2177-4382

Roberto Dall’Agnol, Moacir José Buenano Macambira,

Fish biology, ecology, and behavior

PART I: GEOLOGY, PETROGRAPHY AND GEOCHRONOLOGY.Titanitebiotite 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 Uaupés 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 Uaupés 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 ofO.70631 ± 0.00117, suggesting that the RUG magma formed directily from crustal rocks or was derived from mantle sources but suffered strong crustal contamination.ConcemingthetectonicevolutionofRNP,acontinental collision model is coherent with the available information, but more geological and structural data are necessary to demonstrate this hypothesis.