Fast diffusing Li isotopes provide important insights into the “recent” transient events or processes for both modern and ancient times, but questions remain concerning the large Li isotopic variations of mantle peridotites, which greatly hampers their usage as a geochemical tracer. This study investigates in situ Li content and isotopic profiles of the constituent minerals of abyssal peridotites from the Gakkel Ridge and Southwest Indian Ridge. The complicated and large variations of Li isotopic profiles in Clinopyroxene (Cpx) and Orthopyroxene (Opx) indicate Li isotopic disequilibrium at millimeter scale. The negative correlations of a wide range of Li contents (0.5 to 6.5 ppm) and δ⁷Li values (−10 to +20‰) of olivine, Opx and Cpx grains/relicts, trace element zoning of Cpx, the occurrence of plagioclase, olivine serpentinization along cracks, together with numerical modeling demonstrate the observed Li characteristics to be a manifestation of high‐temperature mineral‐melt Li diffusion during melt impregnation overprinted by low‐temperature mineral‐fluid Li diffusion during dissolution and serpentinization. The preservation of the Li isotopic diffusion profiles requires rapid cooling of 0.3–5°C/year after final‐stage melt impregnation at the Moho boundary, which is consistent with the low temperature at very slow spreadin g ridges caused by conductive cooling. Compared with the well‐studied melt‐rock interaction process, our study indicates that low‐temperature fluid‐rock interaction can induce Li diffusion even in the visibly unaltered mineral relicts of partially altered rocks.

中文翻译：

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深海橄榄岩的锂同位素变化巨大，揭示了快速冷却和熔体/流体-岩石相互作用

快速扩散的锂同位素为现代和古代的“近期”瞬变事件或过程提供了重要的见识，但有关地幔橄榄岩锂同位素的大变化仍然存在疑问，这极大地阻碍了其作为地球化学示踪剂的用途。这项研究调查了来自Gakkel脊和西南印第安脊的深渊橄榄岩的组成矿物的原位Li含量和同位素分布。在斜茂铁（Cpx）和邻苯二茂铁（Opx）中Li同位素分布的复杂和大变化表明，毫米级的Li同位素不平衡。广泛的锂含量（0.5至6.5 PPM）和δ的负相关⁷橄榄石，Opx和Cpx晶粒/遗物的Li值（−10至+20‰），Cpx的微量元素分区，斜长石的出现，沿裂缝的橄榄石蛇纹石化以及数值模拟表明所观察到的Li特征是熔体浸渍过程中的高温矿物熔体Li扩散被溶解和蛇形化过程中的低温矿物流体Li扩散所覆盖。Li同位素扩散分布图的保存需要在Moho边界进行最后阶段的熔体浸渍后，以0.3-5°C /年的速度进行快速冷却，这与传导冷却导致的非常缓慢的扩散脊处的低温相一致。与经过充分研究的熔岩相互作用过程相比，