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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 >Constraints on the age and halogen composition of mantle fluids in Siberian coated diamonds
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Constraints on the age and halogen composition of mantle fluids in Siberian coated diamonds

机译：西伯利亚涂层钻石中地幔流体的年龄和卤素成分的限制

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摘要

Extension of the Ar-Ar stepped heating technique has been used to characterise the Ar, halogen (Cl, Br, I), Ca and K components in seven coated diamonds from the Aikhal kimberlite, Siberia. At least three components have been identified with different Ar isotope compositions. The major component is characterised by high ~(40)Ar/~(36)Ar > 11000 and constant ~(40)Ar~*/Cl (527 ± 22 * 10~(-6)), Br/Cl (1.74 ± 0.18 * 10~(-3)) and I/Cl (22.0 ± 3.4 * 10~(-6)) indicative of a mantle fluid phase. This component is widespread in coated diamonds having been previously reported in samples from Africa and Canada. Estimates of halogen abundances in the sub-continental mantle, based on data from African and Siberian coated diamonds, are 3 ppm Cl, 11 ppb Br and 0.4 ppb I. These low abundances, which are in good agreement with values derived for the depleted asthenospheric mantle derived from MORB data, imply that the upper mantle is >90% degassed of its halogens. A second Ar component in coated stones is most simply understood by in situ decay of ~(40)K and is consistent with the coat-forming event occurring close to the time of host kimberlite eruption 350-380 Ma ago. A third Ar component has a low ~(40)Ar/~(36)Ar ratio (～300), is unassociated with release of K or halogens, and is most likely to be atmospheric blank.
机译：已使用Ar-Ar步进加热技术的扩展来表征来自西伯利亚Aikhal金伯利岩的7颗涂层钻石中的Ar，卤素（Cl，Br，I），Ca和K成分。已鉴定出具有不同的Ar同位素组成的至少三个成分。主要成分的特征是高〜（40）Ar /〜（36）Ar> 11000和恒定〜（40）Ar〜* / Cl（527±22 * 10〜（-6）），Br / Cl（1.74± 0.18 * 10〜（-3））和I / Cl（22.0±3.4 * 10〜（-6））表示地幔流体相。该成分在涂膜钻石中广泛存在，以前在非洲和加拿大的样品中已有报道。根据非洲和西伯利亚涂层钻石的数据，亚大陆幔中的卤素丰度估计值为3 ppm Cl，11 ppb Br和0.4 ppbI。这些低丰度与耗尽的软流圈的值非常吻合来自MORB数据的地幔意味着上地幔的卤素脱气率> 90％。涂层宝石中的第二种Ar成分可以通过〜（40）K的原位衰减来最简单地理解，并且与发生在350-380 Ma以前的主体金伯利岩喷发时间附近发生的涂层形成事件一致。第三个Ar组分的〜（40）Ar /〜（36）Ar比较低（〜300），与K或卤素的释放无关，最有可能是大气空白。

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