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首页> 外文期刊>Geochemistry, geophysics, geosystems >The evolution of MORB and plume mantle volatile budgets: Constraints from fission Xe isotopes in Southwest Indian Ridge basalts
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The evolution of MORB and plume mantle volatile budgets: Constraints from fission Xe isotopes in Southwest Indian Ridge basalts

机译：MORB和羽幔的波动性预算的演变：西南印第安岭玄武岩裂变Xe同位素的制约

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We present high-precision measurements of the fission isotopes of xenon (Xe) in basalts from the Southwest Indian Ridge (SWIR) between 16 degrees E and 25 degrees E. Corrections for syn- to post-eruptive atmospheric contamination yield the Xe isotopic compositions of SWIR mantle sources. We solve for the proportions of mantle Xe derived from the primordial mantle Xe budget, recycling of atmospheric Xe, decay of short-lived I-129, fission of extinct Pu-244, and fission of extant U-238. Xe isotope systematics evident in SWIR basalts and other mantle-derived samples provide new insights into the integrated history of mantle source degassing and regassing. We find that recycled atmospheric Xe dominates the Xe inventories of the SWIR Western and Eastern Orthogonal Supersegment mantle sources (approximate to 80-90% of Xe-132 is recycled in origin), consistent with results from studies of plume-influenced basalts from Iceland and the Rochambeau Rift. While significant regassing of the mantle is evident, we also find differences in the extent of degassing of the MORB and plume sources. MORB sources are consistently characterized by a lower fraction of fission Xe derived from Pu-fission, indicating a greater extent of degassing relative to the plume source. The prevalence of recycled atmospheric Xe in mantle sources indicates incorporation of depleted recycled material even into mantle sources with primitive He and Ne isotopic compositions. Consequently, depleted lithophile isotopic compositions in mantle sources with primitive He and Ne cannot be interpreted as evidence for a nonchondritic bulk silicate Earth.
机译：我们提供了从西南印度洋脊（SWIR）到16度E和25度E之间的玄武岩中氙（Xe）裂变同位素的高精度测量结果。对喷发后大气污染的校正产生了Xe同位素组成SWIR地幔来源。我们解决了原始地幔Xe预算，大气Xe的回收，短命I-129的衰变，绝灭的Pu-244的裂变以及现存的U-238的裂变所产生的地幔Xe的比例。在SWIR玄武岩和其他地幔衍生样品中明显发现的Xe同位素系统学为地幔源脱气和回气的综合历史提供了新见解。我们发现，回收的大气Xe占SWIR西部和东部正交超分割地幔来源的Xe清单的主要部分（约有Xe-132的80-90％是原始回收的），这与来自冰岛和加拿大的羽状玄武岩研究的结果一致。罗尚博裂谷。尽管明显对地幔进行了除气，但我们也发现了MORB和烟羽源除气程度不同。 MORB气源始终以较低的Xu裂变Xe裂变特征为特征，表明相对于烟流气源而言，脱气程度更大。地幔源中普遍存在的再循环大气Xe表明耗尽的再循环物质甚至掺入了具有原始He和Ne同位素组成的地幔源中。因此，地幔源中原始的He和Ne贫化的亲石同位素组成不能解释为非软骨状块状硅酸盐地球的证据。

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