The monitors were fused, and samples heated, using a 6 watt argon-ion laser following the technique described in York et al. (1981) and Layer et al. (1987). Argon purification was achieved using a liquid nitrogen cold trap and a SAES Zr-Al getter at 400C. The samples were then analyzed in a VG-3600 mass spectrometer. Argon isotopes measured were corrected for system blank and mass discrimination, as well as calcium, potassiou and chlorine interference reactions following procedures outlined in McDougall and Harrision (1999).