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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 >Length-scales of chemical and isotopic heterogeneity in the mantle section of the Shetland Ophiolite Complex, Scotland
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Length-scales of chemical and isotopic heterogeneity in the mantle section of the Shetland Ophiolite Complex, Scotland

机译：苏格兰卫生间蛋白质复合物的地幔部分中化学和同位素异质性的长度尺度

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摘要

Kilometre to sub-metre scale heterogeneities have been inferred in the oceanic mantle based on sampling of both ophiolites and abyssal peridotites. The similar to 492 Ma Shetland Ophiolite Complex (SOC) contains a well-preserved mantle section that is dominated by harzburgite (similar to 70 vol.%) previously reported to have variable major and trace element compositions, yet dominantly chondritic initial(187)Os/Os-188 compositions. To assess the preservation of compositional heterogeneities at sub-metre length-scales in the oceanic mantle, a similar to 45 m(2) area of the SOC mantle section was mapped and sampled in detail. Harzburgites, dunites and a pyroxenite from this area were analysed for lithophile and highly-siderophile element (HSE) abundances, as well as for Os-187/Os-188 ratios. Lithophile element data for most rocks are characteristic of supra-subduction zone (SSZ) metasomatic processes. Two dunites have moderately fractionated HSE patterns and suprachondritic gamma Os-(492 Ma) values (+5.1 and +7.5) that are also typical of ophiolitic dunites generated by SSZ melt-rock interactions. By contrast, six harzburgites and four dunites have approximately chondritic-relative abundances of Os, Ir and Ru, and gamma Os-(492 Ma) values ranging only from -0.6 to +2.7; characteristics that imply no significant influence during SSZ processes. Two harzburgites are also characterised by significantly less radiogenic gamma Os (492 ma) values (-3.5 and -4), and yield Mesoproterozoic time of Re depletion (T-RD) model ages. The range of Os isotope compositions in the studied area is comparable to the range reported for a suite of samples representative of the entire SOC mantle section, and approaches the total isotopic variation of the oceanic mantle, as observed in abyssal peridotites. Mechanisms by which this heterogeneity can be formed and preserved involve inefficient and temporally distinct melt extraction events and strong localised channelling of these melts. (C) 201
机译：公里处亚米级规模的非均质性已经推断基于两个蛇绿岩和深海橄榄岩的采样大洋地幔。的类似于492马设德兰蛇绿复合物（SOC）含有保存良好的地幔部由方辉（类似于70体积％）为主的先前报道具有可变主要和微量元素的组合物，但显性球粒初始（187）O的/ OS-188的组合物。为了评估在海洋地幔，类似的45米（2）的SOC地幔部分的面积组成的非均质的子米长度尺度的保存被映射并详细采样。方辉，纯橄岩和从该区域中的石岩进行分析的亲石和高度亲铁元件（HSE）丰度，以及对于OS-187 / OS-188比率。亲石对于大多数岩石元件数据是超俯冲带（SSZ）交代过程的特性。两个纯橄岩已适度分馏HSE图案和suprachondritic伽马OS-（492 Ma）的值（5.1和7.5），其也由典型产生的SSZ蛇绿纯橄岩的熔化 - 岩石相互作用。相比之下，六方辉和四个纯橄岩有Os，Ir和Ru和伽马OS-约球粒-相对丰度（492 Ma）的值的范围从只-0.6到2.7;暗示在SSZ过程没有显著影响的特点。两方辉的特征还在于显著更少放射伽马OS（492毫安）值（-3.5和-4），并产生重新耗尽（T-RD）模式年龄的中元时间。锇同位素组合物在所研究的区域中的范围相当于报道的一套样品代表整个SOC地幔部的的范围内，并接近海洋地幔的总同位素变化，如在深海橄榄岩观察。通过这种异质性，可以形成和保留机制涉及低效和时间不同的熔体提取事件和强定域窜这些熔体的。 （C）201

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