Noble gases in submarine pillow volcanic glasses

Fifteen submarine glasses from the East Pacific Rise (CYAMEX), the Kyushu-Palau Ridge (DSDP Leg 59) and the Nauru Basin (DSDP Leg 61) were analysed for noble gas contents and isotopic ratios. Both the East Pacific Rise and Kyushu-Palau Ridge samples showed Ne excess relative to Ar and a monotonic decrease from Xe to Ar when compared with air noble gas abundance. This characteristic noble gas abundance pattern (type 2, classified by Ozima and Alexander) is interpreted to be due to a two-stage degassing from a noble gas reservoir with originally atmospheric abundance. In the Kyushu-Palau Ridge sample, noble gases are nearly ten times more abundant than in the East Pacific Rise samples. This may be attributed to an oceanic crust contamination in the former mantle source.
There is no correlation between the He content and that of the other noble gas in the CYAMEX samples. This suggests that He was derived from a larger region, independent from the other noble gases.
Except where radiogenic isotopes are involved, all other noble gas isotopic ratios were indistinguishable from air noble gas isotopic ratios. The 3He/4He in the East Pacific Rise shows a remarkably uniform ratio of (1.21 +/- 0.07)*10**-5, while the40Ar/36Ar ranges from 700 to 5600.

本研究对采自东太平洋海隆（East Pacific Rise，CYAMEX）、九州-帕劳海脊（Kyushu-Palau Ridge，DSDP第59航次）与瑙鲁盆地（Nauru Basin，DSDP第61航次）的15件海底玻璃（submarine glasses）样品，开展了稀有气体（noble gas）含量与同位素比值（isotopic ratios）的分析测试。东太平洋海隆与九州-帕劳海脊的样品均表现出相对于氩（Ar）的氖（Ne）过剩特征，且相较于大气稀有气体丰度，从氙（Xe）到氩呈现单调递减的分布规律。这种由Ozima与Alexander划分的第2型特征稀有气体丰度分布模式，被认为源自初始具有大气丰度的稀有气体储库的两阶段脱气作用。九州-帕劳海脊样品的稀有气体丰度约为东太平洋海隆样品的10倍，这一现象可归因于其地幔源区受到了洋壳污染。

在CYAMEX样品中，氦（He）含量与其他稀有气体含量之间不存在显著相关性，这表明氦源自与其他稀有气体无关的更大区域。

除涉及放射成因同位素（radiogenic isotopes）的情况外，其余所有稀有气体同位素比值均与大气稀有气体同位素比值无明显差异。东太平洋海隆样品的3He/4He比值极为均一，为(1.21±0.07)×10^-5，而40Ar/36Ar比值介于700至5600之间。