The origin and significance of poikilitic and mosaic peridotite xenoliths in the western Pannonian Basin

Abstract

Peridotite xenoliths resulting from eruptions of alkali basaltic volcanoes in the western Pannonian Basin can be
divided into two fundamentally contrasting groups. The geochemical characteristics of the abundant protogranular,
porphyroclastic and equigranular nodules suggest that these samples originate from an old, consolidated and
moderately depleted lithospheric mantle domain. In contrast, the geochemical features of the worldwide rare, but in
the Pannonian Basin relatively abundant, poikilitic xenoliths attest to a more complex evolution. It has been argued
that the origin of the peculiar chemistry of these xenoliths may be intimately linked to melt/rock reactions and
chromatographic fractionation in a porous melt-flow system. The most likely site where such reactions could have
taken place is the asthenosphere-lithosphere boundary. In this context, poikilitic xenoliths may provide petrological
and geochemical evidence for reactions between magmatic liquids issued from the emerging and rising
asthenosphere, and the solid mantle rocks of the lithosphere. These reactions are important agents for the thermal
erosion of the lithosphere; thus they could have contributed considerably to the thinning of the lithosphere in the
Pannonian region. Here it is suggested that in the Pannonian Basin there could be a strong relation between the
unusual abundance of poikilitic mantle xenoliths and the strongly eroded lithosphere.