Textural and chemical characterization of glass-bearing mantle xenoliths from Fernando de Noronha, Brazil.

The Fernando de Noronha (FN) archipelago is located in the Atlantic Ocean, 350 km off the coast of NE Brazil. Its volcanism is characterized by multiple eruptions of different ages that have been triggered by intermittent melting of an enriched mantle source. This process is considered to be generated by the FN asthenospheric plume (Lopes & Ulbrich, 2015). The products of the magmatism are three main formations: Remédios, with a potassic and a sodic series, that shows an age (40Ar/39Ar) between 12.5±0.1 and 9.4±0.2 Ma, Sao José formation (9.5±0.4 and 9.0±0.1 Ma), which is the only one hosting mantle xenoliths, and finally Quixaba formation, characterized by nephelinites erupted between 6.2±0.1 and 1.3±0.1 Ma. Many authors focused on mantle xenoliths from this locality, tentatively searching pieces of evidence of the FN mantle plume on the lithosphere. Rivalenti et al. (2000) reported that FN xenoliths show evidence of modal variation induced by reaction with percolating melts. The isotopic analysis performed on their clinopyroxenes were compatible with an EMII type source of metasomatism, same signature as the one of Remédios formation. Kogarko et al. (2001) reported the evidence of carbonate metasomatism. Their model invokes various degrees of partial melting, followed by the percolation of carbonate melts in the depleted mantle. The last model was proposed by Liu et al. (2019), which theorized infiltration of asthenospheric melts inside the lithosphere, followed by reactive percolation of the main magmatism that formed the islands. In this contribute, we present the direct evidence of mantle metasomatism occurred in Fernando de Noronha archipelago. We performed both textural (optical microscopy and 3D X-ray microtomography imaging) and chemical analysis (EMPA and LA-ICP-MS) on K-rich glasses inside the xenoliths to understand the nature, dynamics, and composition of FN mantle section, to test the previous hypothesis and to give new insights on the formation and evolution of potassic rich melts within the lithosphere.