Zircon and apatite-bearing pyroxene hornblendite mantle xenolith from Hungary, Carpathian-Pannonian region

Abstract A composite xenolith composed of a zircon-bearing, apatite-rich olivine-pyroxene hornblendite and an amphibole harzburgite part was found in an outcrop of Neogene alkali basalt at Szigliget, Bakony-Balaton Highland Volcanic Field, Western Hungary. The hornblendite is composed dominantly of amphibole that is strongly enriched in incompatible trace elements along with apatite, orthopyroxene and olivine. Zircon, rutile, ilmenite and sulphide occur as inclusions in the silicate minerals as accessory phases. On the basis of the chemical composition of the minerals, we estimate that the hornblendite crystallized at ~1000–1015 °C and 1.2–1.4 GPa pressure in the uppermost mantle under oxidising conditions (Δlog f O 2 (FMQ)~ + 1.3). The hornblendite precipitated from a volatile and incompatible element-rich silicate melt with trachyte or phonolite composition, which might be derived from an alkali basalt melt by high-degree (>70%) fractional crystallisation.