Samples were analyzed by stepwise heating in SiO2 glass tube, using a Lindberg resistance furnace. Samples were kept at each temperature for 45 min, duning which gas released was cleansed in a three-step procedure using an alcohol/dry ice cold trap, a Ti-sponge getter to 700C, and a Zr-Al getter heated to 100C. Isotopec analyses were carried out on a Varian-MAT GD150 mass spectrometer interfaced to an Apple 2E computer.