Mantle Petrology and Geochemistry Beneath the Nógrád-Gömör Volcanic Field, Carpathian-Pannonian Region

Abstract

Neogene to Quaternary alkali basalts within the Nograd-Gomor Volcanic Field (NGYF) contain abundant mafic and ultramafic xenoliths and megacrysts, yielding insight into the nature and evolution of the mantle beneath this region. The Cr-diopside suite of ultramafic nodules has been classified by texture, mineralogy, and chemistry into two groups: Group 1—spinel lherzolite and spinel websterite, with protogranular to porphyroclastic or equigranular textures and small amounts of pargasitic amphibole; and Group 2—dunite and spinel lherzolite, with “secondary” recrystallized textures and minute amounts of phlogopite. Cr-diopside-rich veinlets occur in Groups 1 and 2, forming composite xenoliths. Calculated bulk-rock compositions and most mineral compositions vary distinctly with texture. “Secondary” recrystallized xenoliths (Group 2) are depleted in “basaltic” major elements, which decrease gradually through equigranular-textured xenoliths towards protogranular to porphyroclastic xenoliths. Nevertheless, withi...