Monazite age and composition from a granite-pegmatite system: A link between pegmatites of the São João del Rei Pegmatitic Province and the newly defined high-K Restinga Metagranite, Minas Gerais, Brazil

Abstract

Monazite geochronology (U–Pb by LA–SF–ICP-MS) and chemical composition by electron microprobe were used to characterize the genetic link between a group of pegmatites from the São João del Rei Pegmatitic Province and a newly defined high-K metagranite of the younger Rhyacian-Orosirian Ritápolis magmatic arc of the Mineiro Belt. The monazite-(Ce) of four samples from the granite and ten from pegmatites yielded the REE pattern of a granite-pegmatite system, where the ∑LREE is similar, but the content of MREE, and Dy increase with the diminution of the crystallization temperature and, consequently, presenting a higher degree of differentiation. The monazite ages of 2022 ± 17 Ma and 2008 ± 8 Ma in the pegmatites correspond to a new event of crystallization of these bodies in the São João del Rei Pegmatitic Province. These pegmatites have a remarkable amount of xenotime and monazite (and absence of cassiterite) and have been characterized as REE-enriched pegmatites. These bodies are connected to the crystallization of an Orosirian high-K metagranite, which has a monazite crystallization age of 2018 ± 31 Ma. This metagranite, proposed here to be named as “Restinga Metagranite”, represents a new and the youngest pluton of the Mineiro Belt, increasing in 90 Ma the evolution time of the Ritápolis magmatic arc (2.19–2.02 Ga), and the Mineiro Belt (2.47–2.02 Ga).