Thallium (Tl) isotope ratios are an emerging tool that can be used to trace crustal recycling processes in arc lavas and ocean island basalts (OIBs). Thallium is a highly volatile metal that is enriched in volcanic fumaroles, but it is unknown whether degassing of Tl from subaerial lavas has a significant effect on their residual Tl isotope compositions. Here, we present Tl isotope and concentration data from degassing experiments that are best explained by Rayleigh kinetic isotope fractionation during Tl loss. Our data closely follow predicted isotope fractionation models in which TlCl is the primary degassed species and where Tl loss is controlled by diffusion and natural convection, consistent with the slow gas advection velocity utilized during our experiments. We calculate that degassing into air should be associated with a net Tl isotope fractionation factor of α_net = 0.99969 for diffusion and natural gas convection (low gas velocities) and α_net = 0.99955 for diffusion and forced gas convection (high gas velocities). We also show that lavas from three volcanoes in the Kamchatka arc exhibit Tl isotope and concentration patterns that plot in between the two different gas convection regimes, implying that degassing played an important role in controlling the observed Tl isotope compositions in these three volcanoes. Literature inspection of Tl isotope data for subaerial lavas reveals that the majority of these appear only minorly affected by degassing, although a few samples from both OIBs and arc volcanoes can be identified that likely experienced some Tl degassing.

中文翻译：

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岩浆脱气过程中的Is同位素分馏：来自实验和堪察加弧熔岩的证据

hall（Tl）同位素比率是一种新兴工具，可用于追踪弧形熔岩和大洋洲玄武岩（OIBs）中的地壳回收过程。hall是一种高度挥发性的金属，富含火山富马酚，但从地下熔岩中对T1脱气是否对其残留的T1同位素组成有显着影响尚不得而知。在这里，我们介绍了脱气实验中的T1同位素和浓度数据，这些数据最好用T1损失期间的瑞利动力学同位素分馏来解释。我们的数据严格遵循预测的同位素分级分离模型，其中TlCl是主要的脱气物质，并且Tl的损失由扩散和自然对流控制，这与我们实验中使用的缓慢气体对流速度一致。α_净 = 0.99969扩散和天然气对流（低气体速度）和α_净 = 0.99955扩散和强制气体对流（高的气体速度）。我们还显示，堪察加弧线中三个火山的熔岩表现出Tl同位素和浓度模式，在两个不同的气体对流方式之间绘图，这表明脱气在控制这三个火山中观测到的Tl同位素组成中起着重要作用。对航空熔岩Tl同位素数据的文献检查表明，尽管可以识别出OIB和弧形火山中的一些样品可能经历了一些Tl脱气，但其中大多数似乎只受到了脱气的轻微影响。