Abstract Understanding metal-silicate differentiation in small rocky bodies that accreted early in solar system history requires quantification of the effects of variable amounts of silicate melt and molten metal on the connectivity of metal-rich liquids. To shed light on this question, the equilibrium geometry and textural ripening of metal grains in the vicinity of the metal interconnection threshold have been determined experimentally. High pressure and temperature experiments were performed in the three-phase system forsterite + silicate melt + nickel at conditions of 1 GPa and up to 2080 K using piston-cylinder and Paris-Edinburgh presses. Sample textures were analyzed by 3D X-Ray microtomography either in-situ at the PSICHE beamline of the SOLEIL synchrotron, or on quenched samples using a laboratory Computed Tomography scan. Although dihedral angles point to textural equilibrium at the scale of individual grains at the end of each experiment, the attainment of textural equilibrium at sample scale is not straightforward. Depending on the relative proportions of the phases, different states of textural maturation are revealed. A particularly important issue is that time-resolved in-situ microtomography data show that cold (subsolidus) compression at the beginning of the experiment leads to soft metal grains being squeezed between silicates, leading to a forced interconnectivity of nickel. High temperature experiments with metal contents ≤20 vol% resulted in disruption of these forced networks, while the networks persisted in time for metal contents ≥25 vol%. This is taken to indicate that the stable interconnection threshold of pure nickel in a partially molten silicate matrix lies between 20 and 25 vol%. Therefore, we conclude that care must be taken when defining the interconnection threshold: not only should there be existence of a network of touching grains, but this network must persist in time in the absence of external forces and at pressure-temperature conditions that permit grain-boundary movement (i.e. excluding kinetically arrested systems). Growth of silicate grains is identified as the process driving textural maturation, and may explain the variability of interconnection thresholds reported in the literature. In addition, these considerations shed light on the diversity of textures observed in natural meteoritic samples (e.g. carbonaceous and ordinary chondrites and primitive achondrites), providing textural arguments to constrain the processes that affected these meteorites.

中文翻译：

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使用 3D 显微断层扫描重新评估部分熔融硅酸盐基质中的金属互连性

摘要 要了解在太阳系历史早期吸积的小岩体中的金属硅酸盐分化，需要量化不同数量的硅酸盐熔体和熔融金属对富含金属的液体的连通性的影响。为了阐明这个问题，已经通过实验确定了金属互连阈值附近金属晶粒的平衡几何形状和纹理成熟。在镁橄榄石 + 硅酸盐熔体 + 镍的三相系统中，在 1 GPa 和高达 2080 K 的条件下使用活塞-气缸和巴黎-爱丁堡压机进行了高压和高温实验。样品质地通过 3D X 射线显微断层扫描在 SOLEIL 同步加速器的 PSICHE 光束线原位或使用实验室计算机断层扫描扫描淬火样品进行分析。尽管在每个实验结束时，二面角指向单个晶粒尺度上的结构平衡，但在样本尺度上达到结构平衡并不简单。根据相的相对比例，揭示了不同的质地成熟状态。一个特别重要的问题是，时间分辨原位显微断层扫描数据显示，实验开始时的冷（亚固相线）压缩导致软金属颗粒被挤压在硅酸盐之间，从而导致镍的强制互连。金属含量≤20 vol% 的高温实验导致这些强制网络的破坏，而当金属含量≥25 vol% 时，网络持续存在。这表明纯镍在部分熔融硅酸盐基质中的稳定互连阈值介于 20 和 25 vol% 之间。因此，我们得出结论，在定义互连阈值时必须小心：不仅应该存在接触谷物的网络，而且该网络必须在没有外力和允许谷物的压力-温度条件下持续存在。 - 边界运动（即不包括动力学停滞系统）。硅酸盐颗粒的生长被确定为驱动结构成熟的过程，并且可以解释文献中报道的互连阈值的可变性。此外，这些考虑阐明了在天然陨石样本中观察到的纹理多样性（例如