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首页> 外文期刊>Contributions to Mineralogy and Petrology >The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization
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The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization

机译：橄榄石结晶塑性变形的遗产：蛇纹石化过程中的高扩散途径

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摘要

Crystal-plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow. Although crystal-plastic deformation and serpentinization are spatio-temporally decoupled, we identified compositional readjustments expressed on the micrometric level as a striped Fe-enriched (X_(Fe) = 0.24 ± 0.02 (zones); 0.12 ± 0.02 (bulk)) or Fe-depleted (X_(Fe) = 0.10 ± 0.01 (zones); 0.13 ± 0.01 (bulk)) zoning in partly serpentinized olivine grains from two upper mantle sections in Norway. Focused ion beam sample preparation combined with transmission electron microscopy (TEM) and aberration-corrected scanning TEM, enabling atomic-level resolved electron energy-loss spectroscopic line profiling, reveals that every zone is immediately associated with a subgrain boundary. We infer that the zonings are a result of the environmental Fe~(2+)Mg~(-1) exchange potential during an-tigorite serpentinization of olivine and the drive toward element exchange equilibrium. This is facilitated by enhanced solid-state diffusion along subgrain boundaries in a system, which otherwise re-equilibrates via dissolution-reprecipitation. Fe enrichment or depletion is controlled by the silica activity imposed on the system by the local olivine/orthopyroxene mass ratio, temperature and the effect of magnetite stability.
机译：晶塑性橄榄石变形以产生由边缘位错组成的亚晶粒边界是软流圈地幔流的必然结果。尽管晶体塑性变形和蛇形化在时空上是分离的，但我们确定了在微米级上表示为富铁条纹（X_（Fe）= 0.24±0.02（区域）; 0.12±0.02（散装））或Fe的成分重新调整挪威两个上地幔部分的部分蛇纹化橄榄石颗粒中的贫化（X_（Fe）= 0.10±0.01（区域）; 0.13±0.01（散装））分区。聚焦离子束样品制备与透射电子显微镜（TEM）和像差校正扫描TEM结合使用，可进行原子级分辨的电子能量损失谱线描图，揭示出每个区域都与亚晶粒边界直接相关。我们推断这些分区是橄榄石的钙铁矿蛇纹石化过程中环境Fe〜（2+）Mg〜（-1）交换势以及对元素交换平衡的驱动的结果。沿着系统中亚晶界增强的固态扩散会促进此过程，否则该扩散会通过溶解-再沉淀而重新平衡。铁的富集或耗竭受局部橄榄石/邻苯二酚质量比，温度和磁铁矿稳定性的影响而施加在系统上的二氧化硅活性所控制。

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