Noble gas analyses were performed in the Roving Automated Rare Gas Analysis (RARGA) laboratory at Lawrence Berkeley National Laboratory, University of California (Kennedy et al., 1985; Hiyagon and Kennedy, 1992). Detailed sample preparation and analytical procedures are discussed for fluid samples and can be found in Kennedy et al. (1985) and Hiyagon and Kennedy (1992).
Approximately 10 to 30 cm3-atm of each gas sample was transferred to a pre-evacuated Cu tube that was subsequently sealed with a refrigeration clamp. Samples in the Cu tubes were then attached to the sample extraction and purification line of the RARGA laboratory that consists of an all-metal gas purification line designed specifically for routine reactive gas cleanup of dirty fluid samples. The extraction system and purification line are connected directly to an all-metal noble gas mass spectrometer laboratory. Each gas sample was analyzed for absolute and relative abundance of isotopes of He, Ne, Ar, Kr, and Xe. Before each sample analysis, a blank was analyzed. In all cases the blanks were <0.1% of the measured Ar composition of the atmosphere. The data has been corrected for mass interference due to HCl and doubly charged 40Ar and 44CO2 and instrumental mass fractionation corrections. Uncertainties related to these corrections were propagated quadratically.
Gas samples were analyzed in two batches of four samples each. The first batch (Samples 996B-1H-1[1], 996C-1H-1[1], 996E-7H-CC[1], and 997A-42X-3[1A]) was analyzed approximately one and a half month after gas collection, whereas the second batch (Samples 994C-31X-7[1], 996B-1H-1[2], 996C-1H-1[2], and 997A-42X-3[1B]) was analyzed approximately seven months after gas collection (Table 2).