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首页> 外文期刊>Nature >EFFECT OF SHALLOW-LEVEL CONTAMINATION ON THE HELIUM ISOTOPE SYSTEMATICS OF OCEAN-ISLAND LAVAS
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EFFECT OF SHALLOW-LEVEL CONTAMINATION ON THE HELIUM ISOTOPE SYSTEMATICS OF OCEAN-ISLAND LAVAS

机译：浅层污染对海洋-岛屿熔岩氦同位素系统的影响

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THE bimodal distribution of helium isotope ratios in ocean-island lavas has provided powerful constraints on the composition and evolution of the Earth's mantle(1-3). 'High-He-3 hotspot' ratios (He-3/He-4 greater than in mid-ocean-ridge basalt, MORB) found on Hawaii(4) and Iceland(5) are thought to trace pristine plumes from the deep(er) mantle, whereas 'low-He-3 hotspot' values (He-3/ He-4 less than or equal to MORB value) at Tristan da Cunha(6) and St Helena(7) are considered to characterize plumes composed (in part) of recycled oceanic or continental crust. Here we report the observation of both 'high-He-3' and 'low-He-3' characteristics(8) in lavas from a single ocean island-Heard Island, in the Indian Ocean. Whereas the high-He-3 lavas provide unambiguous evidence for the involvement of a deep-seated plume in their genesis, we argue that the low He-3/He-4 ratios in other lavas result from shallow-level contamination by radiogenic helium before eruption. These observations call into question the presumed association between low-He-3 ratios (at Heard Island and elsewhere) and ancient crustal material recycled back into the mantle. [References: 30]
机译：大洋-熔岩中氦同位素比率的双峰分布对地幔的组成和演化提供了强有力的约束（1-3）。在夏威夷（4）和冰岛（5）上发现的``高He-3热点''比率（He-3 / He-4比大洋中脊玄武岩更大，MORB）被认为是从深处追溯到原始羽状流（ er）地幔，而Tristan da Cunha（6）和St Helena（7）的“低He-3热点”值（He-3 / He-4小于或等于MORB值）被认为可表征由（部分）回收的海洋或大陆壳。在这里，我们报告了印度洋单个海洋岛-赫德岛的熔岩中“高He-3”和“低He-3”特征的观测结果（8）。高He-3熔岩提供了明确的证据表明深层羽状羽参与了其成因，但我们认为其他熔岩中低的He-3 / He-4比值是由放射性氦在日前的浅水平污染造成的。喷发。这些观察结果使人们怀疑He-3比率低（在希德岛和其他地方）与回收回地幔的古老地壳物质之间的推测联系。 [参考：30]

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