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首页> 外文期刊>Contributions to Mineralogy and Petrology >The effect of chrysotile nanotubes on the serpentine-fluid Li-isotopic fractionation
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The effect of chrysotile nanotubes on the serpentine-fluid Li-isotopic fractionation

机译：温石棉纳米管对蛇纹石液体锂同位素分馏的影响

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We determined the lithium isotope fractionation between synthetic Li-bearing serpentine phases lizardite, chrysotile, antigorite, and aqueous fluid in the P,T range 0.2–4.0 GPa, 200–500°C. For experiments in the systems lizardite-fluid and antigorite-fluid, 7Li preferentially partitioned into the fluid and Δ7Li values followed the T-dependent fractionation of Li-bearing mica-fluid (Wunder et al. 2007). By contrast, for chrysotile-fluid experiments, 7Li weakly partitioned into chrysotile. This contrasting behavior might be due to different Li environments in the three serpentine varieties: in lizardite and antigorite lithium is sixfold coordinated, whereas in chrysotile lithium is incorporated in two ways, octahedrally and as Li-bearing water cluster filling the nanotube cores. Low-temperature IR spectroscopic measurements of chrysotile showed significant amounts of water, whose freezing point was suppressed due to the Li contents and the confined geometry of the fluid within the tubes. The small inverse Li-isotopic fractionation for chrysotile-fluid results from intra-crystalline Li isotope fractionation of octahedral Li[6] with preference to 6Li and lithium within the channels (Li[Ch]) of chrysotile, favoring 7Li. The nanotubes of chrysotile possibly serve as important carrier of Li and perhaps also of other fluid-mobile elements in serpentinized oceanic crust. This might explain higher Li abundances for low-T chrysotile-bearing serpentinites relative to high-T serpentinites. Isotopically heavy Li-bearing fluids of chrysotile nanotubes could be released at relatively shallow depths during subduction, prior to complete chrysotile reactions to form antigorite. During further subduction, fluids produced during breakdown of serpentine phases will be depleted in 7Li. This behavior might explain some of the Li-isotopic heterogeneities observed for serpentinized peridotites.
机译：我们确定了200,500°C的P，T范围内合成的含锂蛇纹石相蜥蜴石，温石棉，蛇纹石和水性流体之间的锂同位素分馏。对于在蜥蜴岩流体和反蛇纹岩流体中的实验， 7 Li优先分配到流体中，Δ 7 Li值遵循含锂云母的T依赖性分馏-流体（Wunder等人，2007）。相比之下，对于温石棉流体实验， 7 Li弱地分配为温石棉。这种相反的行为可能是由于三个蛇纹石品种中的锂环境不同：在蜥蜴石和反蛇纹石中，锂是六重配位的，而在温石棉中，锂是以八面体和含锂的水簇填充纳米管核心的两种方式结合的。温石棉的低温红外光谱测量显示大量水，由于Li含量和管内流体受限的几何形状，水的凝固点得到抑制。八面体Li [6] 的晶体内Li同位素分馏优先于通道内的 6 Li和锂，从而实现了温石棉流体的小Li同位素反分馏（温石棉的Li [Ch] ），偏爱 7 Li。温石棉的纳米管可能是锂的重要载体，也可能是蛇纹石化海洋地壳中其他可流动元素的重要载体。这可能解释了相对于高T蛇纹石，低T温石棉蛇纹石的Li丰度更高。在完成温石棉反应以形成蛇纹岩之前，温和的碳纳米管中的同位素重的含锂流体可以在俯冲过程中在相对浅的深度释放出来。在进一步俯冲过程中，蛇形相分解过程中产生的流体将被消耗在 7 Li中。这种行为可能解释了蛇纹橄榄岩中观察到的锂同位素异质性。

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