Thallium isotopic evidence for ferromanganese sediments in the mantle source of Hawaiian basalts
Thallium isotopic evidence for ferromanganese sediments in the mantle source of Hawaiian basalts
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DOI：
10.1038/nature04450
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发表时间：
2006-01
期刊：
影响因子：
64.8
通讯作者：
S. Nielsen;M. Rehkämper;M. Norman;A. Halliday;D. Harrison
中科院分区：
文献类型：
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作者：
S. Nielsen;M. Rehkämper;M. Norman;A. Halliday;D. Harrison
洋岛玄武岩通常被认为是地幔柱的表面表现，但这种地幔柱源区成分的性质是一个长期争论的主题。在夏威夷爆发的熔岩引起了特别的关注，因为有人提出，186 Os和187 Os的异常反映了与地球金属核的相互作用。然而，最近有人提出，这种变化也可能是由于这些熔岩的地幔源中加入了海洋铁锰沉积物造成的。在这里，我们表明，夏威夷苦橄岩与锇同位素异常也表现出明显的铊同位素的变化，这是再加上铯/铊比延伸到值远低于通常观察到的地幔岩。这种相关性不能通过混合岩芯物质来建立，最好的解释是在夏威夷地幔源区添加了铁锰沉积物。然而，缺乏相关性之间的铊和锇同位素和高铊/锇比值的铁锰沉积物排除沉积起源的锇同位素异常，并离开核幔相互作用作为一个可行的解释夏威夷苦橄岩的锇同位素变化。
Ocean island basalts are generally thought to be the surface expression of mantle plumes, but the nature of the components in the source regions of such mantle plumes is a subject of long-standing debate. The lavas erupted at Hawaii have attracted particular attention, as it has been proposed that coupled186Os and187Os anomalies reflect interaction with the Earth's metallic core,. It has recently been suggested, however, that such variations could also result from addition of oceanic ferromanganese sediments to the mantle source of these lavas,,. Here we show that Hawaiian picrites with osmium isotope anomalies also exhibit pronounced thallium isotope variations, which are coupled with caesium/thallium ratios that extend to values much lower than commonly observed for mantle-derived rocks. This correlation cannot be created by admixing of core material, and is best explained by the addition of ferromanganese sediments into the Hawaii mantle source region. However, the lack of correlation between thallium and osmium isotopes and the high thallium/osmium ratios of ferromanganese sediments preclude a sedimentary origin for the osmium isotope anomalies, and leaves core–mantle interaction as a viable explanation for the osmium isotope variations of the Hawaiian picrites.