Geologia USP. Série Científica (Jul 2018)
U-Pb dating, Lu-Hf isotope systematics and chemistry of zircon from the Morro do Polvilho meta-trachydacite: constraints on sources of magmatism and on the depositional age of the São Roque Group
Abstract
We present new in situ geochronological data of controversial silicic metavolcanic rocks from the lower terrigenous-metavolcanic sequence of the São Roque Group, Ribeira Belt, confirming that they are older than the rocks of higher-metamorphic grade sequences of the Serra do Itaberaba Group. The age of the Polvilho meta-trachydacite was established at 1760 ± 17 Ma, furthermore the results suggest that the bi-modal volcanism of the Boturuna Formation has parent melts from an old (Archean to Paleoproterozoic) continental crust that was melted in a within-plate environment. Trace-element chemistry of zircon, suggests similarities with high-temperature melts (T Zrsat = 900–915ºC) similar to A-type granites (high negative EuN/EuN* and moderate positive CeN/CeN*) from continental sources under reducing conditions.
Keywords