Volatile Element Evidence of Local MORB Mantle Heterogeneity Beneath the Southwest Indian Ridge, 48°–51°E
Volatile Element Evidence of Local MORB Mantle Heterogeneity Beneath the Southwest Indian Ridge, 48°–51°E
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DOI：
10.1029/2021gc009647
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发表时间：
2021-07
期刊：
影响因子：
3.7
通讯作者：
Wei Wang;Katherine A. Kelley;Zhenggang Li;F. Chu;Yunpeng Dong;Ling Chen;Yanhui Dong;Jie Li
中科院分区：
文献类型：
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作者：
Wei Wang;Katherine A. Kelley;Zhenggang Li;F. Chu;Yunpeng Dong;Ling Chen;Yanhui Dong;Jie Li
西南印度洋脊（SWIR）下的地幔源反映了一个复杂的污染历史。岩浆的挥发分含量是这类不均匀性的重要示踪物，它可能会破坏恒定的挥发分/非挥发分元素比，如H2O/Ce比。尽管近年来已有一些研究利用微量元素和同位素数据来研究SWIR 48°-51 ° E地区的地幔源区不均匀性和岩浆作用，但挥发性元素的限制为该地区地幔不均匀性的起源模式提供了有价值的检验。在这里，我们提供了来自48°-51 ° E区域的9个稀有玄武岩玻璃样品的新数据，这使得能够仔细评估初级与次级过程对玻璃挥发物含量的影响。这些样品受到不同程度的碳脱气和富Cl流体的浅同化作用的强烈影响，但也显示出一贯的高H2O/Ce比值（458.8 ± 14.9），在MORB中最高，这不能用晚期次级过程，地壳同化或不同深度的橄榄岩地幔的简单熔融来解释。相反，高的H2O/Ce比值是地幔源组成的特征。48°-51 ° E区域相对于SWIR的其他区域，高度不相容的微量元素明显更贫化，尽管这种贫化在H2O中不明显，H2O在整个SWIR中同样丰富。我们链接在这些玻璃中的高H2O/Ce比与其他微量元素特征诊断的俯冲和流体添加，这表明地幔源反映了耐火地幔残留物，以前熔融的俯冲带内的签名。
The mantle source beneath the Southwest Indian Ridge (SWIR) reflects a complex history of contamination. Magmatic volatile contents are vital tracers of these kinds of heterogeneities, which may fractionate otherwise constant volatile/non‐volatile elemental ratios, such as the H2O/Ce ratio. Although several studies have recently used trace element and isotopic data to address mantle source heterogeneity and magmatic processes at SWIR 48°–51°E region, volatile element constraints provide a valuable test of models for the origins of mantle heterogeneities in this region. Here, we present new data for nine rare basaltic glass samples from the 48°–51°E region, which enable careful assessment of the effects of primary versus secondary processes on the glass volatile contents. These samples are strongly affected by variable extents of carbon degassing, and shallow assimilation of Cl‐rich fluid, but also reveal consistently high H2O/Ce ratios (458.8 ± 14.9), among the highest in MORBs, that cannot be explained by late‐stage secondary processes, crustal assimilation, or simple melting of peridotite mantle at variable depths. Instead, the high H2O/Ce ratios are features of the mantle source composition. The 48°–51°E region is notably more depleted in highly incompatible trace elements relative to other regions of the SWIR, although this depletion is not apparent in H2O, which is similarly abundant throughout the SWIR. We link the high H2O/Ce ratios in these glasses with other trace element characteristics diagnostic of subduction and fluid addition, suggesting that the mantle source reflects signatures of a refractory mantle residue that previously melted within a subduction zone.