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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Th/U and other geochemical evidence for the Reunion plume sampling a less differentiated mantle domain
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Th/U and other geochemical evidence for the Reunion plume sampling a less differentiated mantle domain

机译：Th / U和其他地球化学证据表明留尼汪岛羽流的地幔区域差异较小

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Like Mid-Ocean Ridge Basalts (MORB), most Ocean Island Basalts (0113) record a Th/U decrease during the history of their source. Notable exceptions are lavas sampling EM1 mantle end-member, which have super-chondritic time-integrated Th/U ([Th/U](Pb)). An intermediate situation is observed for the Reunion plume, where both present-day [Th/U] and [Th/U](Pb) are similar to the bulk Earth value (weight ratio similar to 3.9). If [Th/U] measured in basalts reliably reflects the source ratio, then the Reunion plume source could have evolved in closed system with respect to Th/U. Th/U decrease in the mantle has been ascribed either to early continental crust extraction, or to preferential recycling of U over Th since oxidizing conditions appeared at the surface of the planet (similar to 2.2 Ga). The primitive-like Th/U signature of Reunion is best explained by the absence of subduction influence since at least the Archean. This possibility is consistent with the Os-187/Os-186 signature, which is the less radiogenic of ocean island shield basalts. In addition, the difference in He-3/He-4 between Reunion (R/R-A similar to 12.5) and high-He-3/He-4 plumes (Hawaii, Iceland) most likely reflects a Reunion source less depleted in U and Th, rather than more degassed. In Sr-Nd-Pb-Os-He isotope space, Reunion signature plots in the region where OIB arrays converge, suggesting that the Reunion plume samples a component common to 0113, which is neither the source of MORB, nor the region where subducted plates are stored. It is suggested that the Reunion plume taps an early-depleted mantle domain subsequently influenced little, or not at all by recycling processes. (c) 2006 Elsevier B.V. All rights reserved.
机译：与大洋中部玄武岩（MORB）一样，大多数大洋洲玄武岩（0113）在其起源历史中均记录了Th / U降低。值得注意的例外是熔岩采样EM1地幔末段，其具有超软骨时间积分的Th / U（[Th / U]（Pb））。在团聚羽中观察到一个中间情况，其中当前的[Th / U]和[Th / U]（Pb）都与大块地球值相似（重量比类似于3.9）。如果用玄武岩测得的[Th / U]能够可靠地反映出源比，那么团聚羽状源就可能在封闭系统中相对于Th / U演化了。地幔中Th / U的减少归因于早期大陆壳的提取，或者归因于行星表面出现了氧化条件（类似于2.2 Ga），U优先于Th循环利用。团聚的原始Th / U签名最好是因为至少从太古宙以来没有俯冲影响。这种可能性与Os-187 / Os-186签名一致，Os-187 / Os-186签名是海洋岛屿盾牌玄武岩的放射源较少。此外，团聚（R / RA与12.5相似）与高He-3 / He-4羽（冰岛夏威夷）之间的He-3 / He-4差异很可能反映出团聚源中U和E的消耗较少。 ,，而不是更多的脱气。在Sr-Nd-Pb-Os-He同位素空间中，团聚体特征图在OIB阵列收敛的区域内绘制，这表明团聚体羽流采样了0113公用的分量，该分量既不是MORB的来源，也不是俯冲板块的区域被存储。有人建议，留尼汪岛的羽拍使用的是早期枯竭的地幔区域，随后几乎没有受到回收过程的影响，甚至完全没有受到回收过程的影响。 （c）2006 Elsevier B.V.保留所有权利。

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