Dating high-grade matemorphic mineral growth in the Haast schist using U-PB tims

One of the persistent problems in Haast Schist geology has been precise determination of the time of peak metamorphic mineral growth. This is particularly difficult in the amphibolite facies Alpine Schist where K-Ar, Ar-Ar and fission track data have yielded Cenozoic exhumation ages, yet it is believed by many that the index minerals grew in the Mesozoic. After searching unsuccessfully for monazite in high-grade Alpine Schist, we conducted a pilot U-Pb TIMS investigation that focussed on the mineral geochronometer titanite. We conclude that U-Pb titanite geochronology can demonstrably penetrate the Alpine 'uplift veil' that has hitherto prevented establishment of peak crystallisation ages of Haast Schist metamorphic minerals. Further U-Pb work is in progress. (author)