The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization
The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization
复制标题
橄榄石晶体塑性变形的遗产：蛇纹石化过程中的高扩散路径
DOI：
10.1007/s00410-011-0695-3
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发表时间：
2012
影响因子：
3.5
通讯作者：
H. Austrheim
中科院分区：
文献类型：
--
作者：
O. Plümper;H. King;C. Vollmer;Q. Ramasse;H. Jung;H. Austrheim
晶体塑性橄榄石变形产生由刃型位错组成的亚晶界是软流圈地幔流动的必然结果。尽管晶体塑性变形和蛇纹石化在时空上是解耦的，但我们在挪威两个上地幔剖面的部分蛇纹石化橄榄石颗粒中发现了微米级的成分再调整，表现为条带状的富铁（$\bar{X}_{\text{Fe}}$ = 0.24 ± 0.02（区域）；0.12 ± 0.02（整体））或贫铁（$\bar{X}_{\text{Fe}}$ = 0.10 ± 0.01（区域）；0.13 ± 0.01（整体））分带。聚焦离子束样品制备结合透射电子显微镜（TEM）和像差校正扫描TEM，能够进行原子级分辨的电子能量损失光谱线分析，结果表明每个区域都直接与一个亚晶界相关联。我们推断这些分带是橄榄石叶蛇纹石化过程中环境的Fe²⁺Mg⁻¹交换势以及趋向元素交换平衡的结果。在一个系统中，沿亚晶界的固态扩散增强促进了这一过程，否则该系统会通过溶解 - 再沉淀重新达到平衡。铁的富集或贫化受局部橄榄石/斜方辉石质量比、温度以及磁铁矿稳定性所施加给系统的二氧化硅活度控制。两种分带类型与叶蛇纹石之间的Fe - Mg交换系数$K_{\text{D}}^{{{\text{Atg}}/{\text{Ol}}}}$趋向于交换平衡。与未受影响的整体成分相比，两种分带类型中锰都富集，镍都贫化。沿橄榄石亚晶界纳米级、不均匀分布的叶蛇纹石沉淀表明水能够沿着它们进入。通过电子背散射衍射获得的橄榄石颗粒区域与不同蛇纹石脉世代之间的晶体学取向关系支持了蛇纹石化是沿着橄榄石亚晶界开始的这一假设。
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 ($$ \bar{X}_{\text{Fe}} $$ = 0.24 ± 0.02 (zones); 0.12 ± 0.02 (bulk)) or Fe-depleted ($$ \bar{X}_{\text{Fe}} $$ = 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 Fe2+Mg−1 exchange potential during antigorite 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. The Fe-Mg exchange coefficients $$ K_{\text{D}}^{{{\text{Atg}}/{\text{Ol}}}} $$ between both types of zoning and antigorite display coalescence toward exchange equilibrium. With both types of zoning, Mn is enriched and Ni depleted compared with the unaffected bulk composition. Nanometer-sized, heterogeneously distributed antigorite precipitates along olivine subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries.
DOI：
10.1093/jmicro/dfp052
发表时间：
2010-04-01
期刊：
JOURNAL OF ELECTRON MICROSCOPY
影响因子：
--
作者：
Buban, James P.;Ramasse, Quentin;Stahlberg, Henning
通讯作者：
Stahlberg, Henning