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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 >Concomitant occurrence of primordial and recycled noble gases in the Earth's mantle
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Concomitant occurrence of primordial and recycled noble gases in the Earth's mantle

机译：地球地幔中同时发生原始和回收的稀有气体

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Helium and argon concentrations and isotopic compositions have been determined for a suite of fresh alpine-type peridotites from the Horoman ultramafic complex, Hokkaido, Japan. Crushing and heating gas extractions on the samples yielded quite uniform ~3He/~4He and ~4He/~(40)Ar_(na(=non-atmospheric)) ratios of 7.7-9.2 Ra and 1.5-3.4, respectively. These values are consistent with those suggested for a mantle source for mid-oceanic ridge basalts (MORBs) (～8 Ra, 1.4-4.5, respectively). In contrast to these apparent affinities with a MORB component, the observed ~(40)Ar/~(36)Ar ratios (330-470) appeared to be significantly lower than the suggested MORB source value of >40 000, indicating that virtually all ~(36)Ar resides in fluid inclusions should be of atmospheric origin. Intriguingly, the amounts of ~(36)Ar in the samples showed a clear positive correlation with those of ~3He (= the isotope which can safely be regarded as a primordial mantle component). The correlation between primordial and atmospheric components cannot be explained by shallow-level atmospheric contamination. Rather, we infer that an atmospheric component is of recycled origin which had introduced into the mantle by the subducting slab when the complex was at a mantle wedge setting. Infiltration of metasomatic fluid or melt produced in the mantle wedge above the subducting slab would result in fluid inclusions being formed with noble gas signatures like those observed in the samples. This would be the first compelling evidence that some fraction of recycled atmospheric noble gases derived from the subducting slab could have been preserved in the mantle without returning to the atmosphere through arc volcanism.
机译：已经确定了来自日本北海道Horoman超镁铁质复合体的一组新鲜高山型橄榄岩的氦气和氩气浓度以及同位素组成。样品的粉碎和加热气体提取分别产生了7.7-9.2 Ra和1.5-3.4的相当均匀的〜3He /〜4He和〜4He /〜（40）Ar_（na（=非大气））比。这些值与洋中脊玄武岩（MORBs）的地幔来源所建议的值一致（分别为〜8 Ra，分别为1.4-4.5）。与这些具有MORB成分的表观亲和力相反，观察到的〜（40）Ar /〜（36）Ar比（330-470）明显低于建议的MORB源值> 40 000，这表明几乎所有〜（36）Ar包裹在流体中的夹杂物应源自大气。有趣的是，样品中〜（36）Ar的量与〜3He的量呈明显的正相关关系（=同位素可以安全地视为原始地幔组分）。原始和大气成分之间的相关性不能用浅层大气污染来解释。相反，我们推断大气成分是可循环利用的，当复合体处于地幔楔形位置时，它被俯冲板引入地幔。在俯冲板上方的地幔楔中产生的交代流体或熔体的渗透将导致形成流体包裹体，这些包裹体具有稀​​有气体特征，就像在样品中观察到的那样。这将是第一个令人信服的证据，表明某些来自俯冲平板的再循环大气稀有气体本来可以保存在地幔中，而不会通过弧火山作用返回大气。

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