Stuart Finlay M, Lass-Evans Solveigh, Fitton J Godfrey, Ellam Robert M
Isotope Geosciences Unit, Scottish Universities Environmental Research Centre, East Kilbride G75 0QF, UK.
Nature. 2003 Jul 3;424(6944):57-9. doi: 10.1038/nature01711.
The high 3He/4He ratio of volcanic rocks thought to be derived from mantle plumes is taken as evidence for the existence of a mantle reservoir that has remained largely undegassed since the Earth's accretion. The helium isotope composition of this reservoir places constraints on the origin of volatiles within the Earth and on the evolution and structure of the Earth's mantle. Here we show that olivine phenocrysts in picritic basalts presumably derived from the proto-Iceland plume at Baffin Island, Canada, have the highest magmatic 3He/4He ratios yet recorded. A strong correlation between 3He/4He and 87Sr/86Sr, 143Nd/144Nd and trace element ratios demonstrate that the 3He-rich end-member is present in basalts that are derived from large-volume melts of depleted upper-mantle rocks. This reservoir is consistent with the recharging of depleted upper-mantle rocks by small volumes of primordial volatile-rich lower-mantle material at a thermal boundary layer between convectively isolated reservoirs. The highest 3He/4He basalts from Hawaii and Iceland plot on the observed mixing trend. This indicates that a 3He-recharged depleted mantle (HRDM) reservoir may be the principal source of high 3He/4He in mantle plumes, and may explain why the helium concentration of the 'plume' component in ocean island basalts is lower than that predicted for a two-layer, steady-state model of mantle structure.
被认为源自地幔柱的火山岩具有高的3He/4He比值，这被视作存在一个自地球吸积以来基本未脱气的地幔储库的证据。该储库的氦同位素组成限制了地球内部挥发物的起源以及地幔的演化和结构。我们在此表明，加拿大巴芬岛推测源自原始冰岛地幔柱的苦橄质玄武岩中的橄榄石斑晶具有迄今记录到的最高岩浆3He/4He比值。3He/4He与87Sr/86Sr、143Nd/144Nd以及微量元素比值之间的强相关性表明，富含3He的端元存在于源自亏损上地幔岩石的大量熔体的玄武岩中。该储库与在对流隔离储库之间的热边界层处少量原始富挥发物的下地幔物质对亏损上地幔岩石的再补给相一致。来自夏威夷和冰岛的具有最高3He/4He比值的玄武岩落在观测到的混合趋势上。这表明一个3He再补给的亏损地幔（HRDM）储库可能是地幔柱中高3He/4He的主要来源，并且可能解释了为什么大洋岛玄武岩中“地幔柱”组分的氦浓度低于地幔结构的两层稳态模型所预测的浓度。
