Na-alkali silicate metasomatism in mantle xenoliths from Southern Alps (Veneto Volcanic Province)

The peridotitic xenoliths hosted by the Paleogenic lavas of the Veneto Volcanic Province (Southern Alps, Italy) are mainly constituted by spinel-bearing lherzolites, with subordinate harzburgites. All the xenoliths show protogranular textures represented by well-equilibrated assemblage of olivine, orthopyroxene, clinopyroxene and spinel. Superimposed pyrometamorphic textures are widespread, with the development of secondary phases in reaction relationships with primary paragenesis: Type A texture is characterised by reaction areas around orthopyroxene (in contact with spinel), generating a secondary assemblage made up of small crystals of olivine, clinopyroxene, feldspar, spinel and glass in decreasing order of abundance. Type B1 and B2 textures are similar to the previous one, but comparatively greater glass abundance within the secondary phases is observed. In B1 glass is usually black or dark brown in colour with skeletal feldspar often associated with it. In B2 glass is pale brown,...