Abstract Many volcanic hotspots are connected via ‘plume’ conduits to thermochemical structures with anomalously low seismic velocities at the core-mantle boundary. Basaltic lavas from some of these hotspots show anomalous daughter isotope abundances for the short-lived 129I-129Xe, 146Sm-142Nd, and 182Hf-182W radioactive decay systems, suggesting that their lower mantle sources contain material that dates back to Earth-forming events during the first 100 million years in solar system history. Survival of such ‘primordial’ remnants in Earth's mantle places important constraints on the evolution and inner workings of terrestrial planets. Here we report high-precision 182W/184W measurements for a large suite of kimberlite volcanic rocks from across the African tectonic plate, which for the past 250 million years has drifted over the most prominent thermochemical seismic anomaly at the core-mantle boundary. This so-called African LLSVP, or ‘large low shear-wave velocity province’, is widely suspected to store early Earth remnants and is implicated as the ultimate source of global Phanerozoic kimberlite magmatism. Our results show, however, that kimberlites from above the African LLSVP, including localities with lower mantle diamonds such as Letseng and Karowe Orapa A/K6, lack anomalous 182W signatures, with an average μ 182 W value of 0.0 ± 4.1 (2SD) for the 18 occurrences studied. If kimberlites are indeed sourced from the African LLSVP or superplume, then the extensive 182W evidence suggests that primordial or core-equilibrated mantle materials, which may contribute resolvable μ 182 W excesses or deficits, are only minor or locally concentrated components in the lowermost mantle, for example in the much smaller ‘ultra-low velocity zones’ or ULVZs. However, the lack of anomalous 182W may simply suggest that low-volume kimberlite magmas are not derived from hot lower mantle plumes. In this alternative scenario, kimberlite magmas originate from volatile-fluxed ambient convecting upper mantle domains beneath relatively thick and cold lithosphere from where previously ‘stranded’ lower mantle and transition zone diamonds can be plucked.

中文翻译：

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非洲超羽流上方金伯利岩的钨 182 记录：探索与地核-地幔边界的联系

摘要 许多火山热点通过“羽流”管道与地核-地幔边界处具有异常低地震速度的热化学结构相连。其中一些热点的玄武岩熔岩显示出短寿命的 129I-129Xe、146Sm-142Nd 和 182Hf-182W 放射性衰变系统的异常子同位素丰度，这表明它们的下地幔源包含可追溯到地球形成事件的物质太阳系历史上的第一个 1 亿年。地球地幔中这种“原始”遗迹的生存对类地行星的演化和内部运作构成了重要限制。在这里，我们报告了对来自非洲构造板块的大量金伯利岩火山岩的高精度 182W/184W 测量结果，在过去的 2.5 亿年里，它一直飘过地核-地幔边界最显着的热化学地震异常。这个所谓的非洲 LLSVP，或“大的低剪切波速度区”，被广泛怀疑储存着早期的地球遗迹，并被认为是全球显生宙金伯利岩岩浆活动的最终来源。然而，我们的结果表明，来自非洲 LLSVP 上方的金伯利岩，包括拥有下地幔钻石的地区，如 Letseng 和 Karowe Orapa A/K6，缺乏异常的 182W 特征，平均 μ 182 W 值为 0.0 ± 4.1 (2SD)研究了 18 次。如果金伯利岩确实来自非洲 LLSVP 或超级羽流，那么广泛的 182W 证据表明原始或核心平衡的地幔物质可能导致可分辨的 μ 182 W 过剩或不足，仅是最下地幔中的次要或局部集中成分，例如在小得多的“超低速带”或 ULVZ 中。然而，异常 182W 的缺乏可能只是表明低体积金伯利岩浆并非来自热的下地幔柱。在这种替代方案中，金伯利岩浆起源于相对厚而冷的岩石圈下方的挥发物流动环境对流上地幔域，​​从那里可以采摘先前“搁浅”的下地幔和过渡带钻石。