Comment on “Atmospheric contamination: A possible source for heavy noble gases in basalts from Loihi Seamount, Hawaii” by D. B. Patterson, M. Honda, and I. McDougall

Abstract

Allègre et al. (1983), Staudacher et al. (1986) and Sarda et al. (1988) reported noble gas concentrations and isotopic ratios of basalt glasses from Loihi seamount and Hualalai, Hawaii. The 4He/3He and 40Ar/36Ar ratios of ∼25,000 and 390 ± 50 respectively are different than the air ratio and typical ratios found in MORB glasses. The Ne, Kr and Xe isotopic ratios are the same as those found in air or deep seawater. Based on the different isotopic ratios and the different noble gas concentration patterns of Ne, Ar, Kr and Xe compared to air, deep seawater and MORB, these authors concluded that the noble gases enclosed in vesicles from Loihi and Hualalai basalts are not significantly contaminated by atmospheric noble gases, and that the Loihi and Hualalai basalts came from a separate source, namely the lower mantle, with a distinct noble gas signature. In contrast to the upper mantle, which is highly depleted in noble gases, this lower mantle should be not or only slightly outgassed (Allègre et al., 1986).In a recent publication, Patterson et al. (1990), based on our noble gas data (Staudacher et al., 1986; Sarda et al., 1988), propose that Ne, Ar, Kr and Xe noble gas concentrations in basalt glasses could be plausibly explained by a) contamination of the Loihi plume magma prior to eruption with atmospheric noble gases disolved in deep seawater (which they model by elemental noble gas fractionation of a tholeiitic melt that was equilibrated with seawater derived noble gases), and b) elemental fractionation of noble gases during vesicle formation and vesicle loss. We completely disagree with such an interpretation and show here that their argumentation is inconsistent and incorrect.