Lower crustal zircons reveal Neogene metamorphism beneaththe Pannonian Basin (Hungary)

Abstract

Neogene alkaline intraplate volcanic depositsin the Pannonian Basin (Hungary) contain many lowercrustal granulite-facies xenoliths. U-Pb ages have been determinedfor zircons separated from a metasedimentaryxenolith, using LA-ICPMS and SHRIMP techniques. Thezircons show typical metamorphic characteristics and arenot related to the hostmagmatism. The oldest age recordedis late Devonian, probably related to Variscan basementlithologies. Several grains yield Mesozoic dates for theircores, which may correspond to periods of orogenic activity.Most of the zircons show young ages, with some beingPalaeocene-Eocene, but the majority being youngerthan 30Ma. The youngest zircons are Pliocene (5.1-4.2 Ma)and coincide with the age of eruptions of the host alkalibasalts. Such young zircons, so close to the eruption age,are unusual in lower crustal xenoliths, and imply that theheat flow in the base of the Pannonian Basin was sufficiently high to keep many of them close to their blockingtemperature. This suggests that metamorphism is continuingin the lower crust of the region at the present day.

Keywords

• xenolith
• zircons
• lower crust
• pannonianbasin