AI 中文总结
本研究通过多种表征技术揭示天然玄武岩橄榄石晶界的结构与微量元素特征，发现其为不相容元素的纳米级储存库，需纳入微量元素质量平衡计算。
AI 中文摘要
晶界在多晶橄榄石中普遍存在，但其结构和微量元素化学特征仍缺乏充分约束。我们通过关联电子背散射衍射、透射电子显微镜和原子探针层析技术，表征了来自留尼汪岛富尔奈斯火山和夏威夷冒纳罗亚火山的未变形橄榄石集合体中的晶界。这些晶界为结晶态，结构宽度约1 nm，未观测到连续玻璃质薄膜；Ca、Al、P、Na和Ti呈选择性富集，而Mg、Fe、Ni和Mn保持均匀分布。多个富集质量窗口与名义稀土元素离子位置重合，但未分辨的等压线及缺乏诊断性同位素包络线无法实现可靠归属。二价阳离子偏析遵循离子尺寸失配趋势，而异价离子偏离则受未约束因素影响。Ca的界面过量为2.94-2.97原子/平方纳米，相当于0.327-0.330单分子层，接近Hiraga等人（2004）报道的1523 K平衡偏析等温线上限，处于玄武岩橄榄石结晶温度范围内，这支持晶界形成于晶体生长过程，尽管晶群聚集后经高温停留也可产生类似特征。Ca的化学宽度约为6-9 nm，富集程度最高的元素的化学宽度可达10-15 nm，表明狭窄的结构核心与较宽的化学偏析之间存在解耦。与已发表的变形橄榄石原子探针数据相比，这些晶界保留了更宽的富集晕，但分析差异使得该对比具有不确定性。因此，橄榄石晶界构成了一个独特的纳米级储存库，应与晶体内部和残余熔体一同纳入富橄榄石集合体的微量元素质量平衡计算中。
英文摘要
Grain boundaries are pervasive in polycrystalline olivine, yet their structure and trace-element chemistry remain poorly constrained. We characterize boundaries in undeformed olivine aggregates from Piton de la Fournaise (La Reunion) and Mauna Loa (Hawaii) by correlating electron backscatter diffraction, transmission electron microscopy, and atom probe tomography. The boundaries are crystalline, with a structural width of about 1 nm and no continuous glassy film resolved. Ca, Al, P, Na, and Ti are selectively enriched, whereas Mg, Fe, Ni, and Mn remain homogeneous. Several enriched mass windows coincide with nominal rare-earth-element ion positions, but unresolved isobars and the lack of a diagnostic isotope envelope preclude secure assignments. Divalent-cation segregation follows an ionic-size-misfit trend, while aliovalent departures require unconstrained contributions. The Ca interfacial excess is 2.94-2.97 atoms per square nanometer, equivalent to 0.327-0.330 monolayers, and lies near the upper published 1523 K equilibrium segregation isotherm of Hiraga et al. (2004), within the range of basaltic olivine crystallization temperatures. This supports boundary formation during crystal growth, although synneusis followed by high-temperature residence could produce a similar signature. Ca chemical widths are about 6-9 nm, and those of the most strongly enriched elements reach about 10-15 nm, demonstrating decoupling between the narrow structural core and broader chemical segregation. Compared with published atom-probe data on deformed olivine, these boundaries preserve broader halos, although analytical differences make the contrast tentative. Olivine grain boundaries therefore constitute a distinct nanoscale reservoir that should be included alongside crystal interiors and residual melt in trace-element mass balances of olivine-rich aggregates.
Comments46 pages; 10 main figures and 10 supplementary figures; supplementary text and tables included
