Abstract Clinopyroxene crystals of various origins occur in the unusually crystal-
and xenolith-rich alkaline basalts of the Bondoró-hegy and the Füzes-tó scoria cone,
which are the youngest eruptive centres in the Bakony-Balaton Highland Volcanic Field,
western Pannonian Basin. The clinopyroxenes show diverse textural and zoning features
as well as highly variable major and trace element chemistry. Xenocryst, megacryst
and phenocryst crystal populations can be distinguished on the basis of their compositional
differences. The trace element patterns of green clinopyroxene cores display a large
range in composition and indicate that most of them have a metamorphic origin. Most
of them were incorporated from lower crustal mafic granulite wall rocks, whilst only
a few of them are of magmatic origin representing pyroxenite (Type II) cumulates.
The colourless clinopyroxene xenocrysts reflect the texturally and geochemically diverse
nature of the subcontinental lithospheric mantle beneath the studied area, mainly
representing regions characterized by various stages of metasomatism. The colourless
and green megacrysts are genetically related to each other, having crystallised as
early and late crystallisation products, respectively, from petrogenetically related
melts as part of a fractional crystallisation sequence. These melts represent earlier
alkaline basaltic magmas (as represented by the Type II xenoliths), having stalled
and crystallised near the crust-mantle boundary in the uppermost part of the mantle.
This serves as evidence that the deep magmatic systems beneath monogenetic volcanic
fields are complex, involving several phases of melt generation, accumulation and
fractionation at variable depths. We show that in situ trace element analysis is necessary
in order to unravel the origins and relationships of the diverse clinopyroxene populations.
Such studies significantly contribute to our understanding of the ascent histories
of alkaline basaltic magmas as well as provide information about the characteristics
of the rocks which constitute the lithosphere. Additionally, the abundance of foreign
crystals incorporated in the ascending basaltic magmas, and their potential for contamination
of the host magma, must be taken into account when whole-rock geochemical data are
interpreted.
