Boron metasomatism in the Brabant Massif (Belgium): Geochemical and petrographical evidence of Devonian tourmalinite pebbles

Abstract

New petrographical and geochemical evidence of tourmalinite pebbles from two Lower and three Middle Devonian formations from Belgium is presented. Petrography, REE, transition metal and microprobe data of the studied rocks suggest it are (meta)sediment-derived tourmalinites formed by boron metasomatism (and hydrothermal brecciation) in an intrusive setting. Tourmaline mineralizations within eastern Avalonia are known in south-east Ireland, the English Lake District and East Anglia. Based on previously suggested relations between Early Palaeozoic igneous activity in last two mentioned regions and the Brabant Massif, it is presumed that the Brabant Massif also underwent granite-related tourmalinization and that this was the source of the studied pebbles. Petrologie differences between pebbles found in Middle Devonian formations and pebbles from Lower Devonian formations, suggest that fluid circulation occurred on a regional scale, possibly extending into the Stavelot massif.