U-Pb zircon age constraints for the Ordovician Fishguard Volcanic Group and further evidence for the provenance of the Stonehenge bluestones.

New U-Pb zircon ages from rhyolite samples of the Fishguard Volcanic Group, SW Wales, confirm a Middle Ordovician (Darriwilian) age for the group. One of the samples is from Craig Rhos-y-felin, which has recently been identified on petrological and geochemical grounds as the source of much of the debitage (struck flakes) at Stonehenge. Analysis of a Stonehenge rhyolite fragment yields an age comparable with that of the Craig Rhos-y-felin sample. Another Stonehenge fragment, thought to come from orthostat (standing stone) 48 and on petrographical grounds to be derived from the Fishguard Volcanic Group (but not Craig Rhos-y-felin), yields an age also consistent with a Fishguard Volcanic Group source. [ABSTRACT FROM AUTHOR]