Syn-volcanic melt-rock reactions recorded in peridotitic xenoliths from Scania, S Sweden

Abstract

Peridotite xenoliths from Scania (S Sweden), brought to the surface by Mesozoic basanitic magmas, provide insights into the lithospheric mantle underlying the East European Craton. During their ascent, some of the entrained xenoliths were infiltrated by a Si-undersaturated melt. The infiltration triggered orthopyroxene dissolution and the formation of fine-grained olivine, clinopyroxene and Si-rich glasses (trachytic/trachydacitic and dacitic). The latter interacted with clinopyroxene and/or spinel creating spongy rims of various thicknesses (from few to hundreds of μm). The reactions varied in intensity and effect depending on the distance from the xenolith margin and the duration of the reaction time. At the outer parts of xenoliths, intense reactions dissolved orthopyroxene entirely, forming spongy rims on spinel and clinopyroxene, while inner sections showed limited reactions, primarily between mafic melts and orthopyroxene. The local reheating and melting of fine-grained aggregates during the ascent of xenoliths resulted in the formation of a hydrous, high-Mg, glass-like phase.