Mineralogy and U/Pb geochronology of beryl and columbite-tantalite pegmatites in the Serido pegmatite district, northeastern Brazil

摘要

The Serido fold belt is the host to abundant pegmatites mined for columbite-tantalite, beryl and gem quality tourmaline. The δ~(18)O values of quartz and muscovite from the pegmatites reveal oxygen isotopic reequilibration at low temperatures and/or external contamination. Six U-Pb ages of columbite fall between 509.5 +- 2.9 and 514.9 +- 1.1 Ma. Monazite from peraluminous granite, genetically related to pegmatites yields an age of 535 +- 4.1 Ma. The latter and the heterogeneous pegmatites are interpreted as two distinct and successive magmatic events from a common, deep reservoir, using the same structures during their crustal ascent.