Mineral chemistry of mica-pyroxenite xenoliths in neoproterozoic ultrapotassic syenitic magmas, NE Brazil

Mica-pyroxenite xenoliths found in Neo Proterozoic ultrapotassic syenitic magmas northeastern Brazil, present modal phases, textural relationships, bulk-rock and mineral chemistries compatible with metasomatic alteration, they suffered in the mantle source. These inclusions are mainly composed of diopside-salite ( >80% of the bulk rock), with subordinate, in variable amounts, F-rick phlogopite, calcite, hyalophane, sphene, apatite and traces of barite. Corrosion of pyroxene is observed in the vicinity of these late space-filling materials. In this paper, mineral chemistry data for the pyroxenite xenoliths are used to explain the chemical fingerprints of their host syenites, and to show that xenoliths record metasomatism in the mantle source, for the ultrapotassic magmas in this part of Brazil. 12 figs., 1 tab