Research School of Earth Sciences, Australian National University, 142 Mills Road, Acton, ACT 2601, Australia.
Earth and Atmospheric Sciences, University of Alberta, 116 Street and 85 Avenue, Edmonton, Alberta T6G 2R3, Canada.
Science. 2019 Aug 16;365(6454):692-694. doi: 10.1126/science.aax5293.
Isotope compositions of basalts provide information about the chemical reservoirs in Earth's interior and play a critical role in defining models of Earth's structure. However, the helium isotope signature of the mantle below depths of a few hundred kilometers has been difficult to measure directly. This information is a vital baseline for understanding helium isotopes in erupted basalts. We measured He-Sr-Pb isotope ratios in superdeep diamond fluid inclusions from the transition zone (depth of 410 to 660 kilometers) unaffected by degassing and shallow crustal contamination. We found extreme He-C-Pb-Sr isotope variability, with high He/He ratios related to higher helium concentrations. This indicates that a less degassed, high-He/He deep mantle source infiltrates the transition zone, where it interacts with recycled material, creating the diverse compositions recorded in ocean island basalts.
玄武岩的同位素组成提供了有关地球内部化学储层的信息，对于定义地球结构模型起着至关重要的作用。然而，几百公里以下地幔的氦同位素特征一直难以直接测量。这些信息是理解喷发玄武岩中氦同位素的重要基准。我们测量了来自过渡带（深度为 410 至 660 公里）的未经脱气和浅层地壳污染影响的超深金刚石流体包裹体中的 He-Sr-Pb 同位素比值。我们发现了极端的 He-C-Pb-Sr 同位素变化，其中高 He/He 比值与更高的氦浓度有关。这表明，较少脱气的、高 He/He 的深部地幔源渗透到过渡带，在那里与再循环物质相互作用，形成了在大洋岛屿玄武岩中记录的不同组成。
