Mixing of low δ⁷Li sediment components (δ⁷Li(‰) = 1000 × [(⁷Li/⁶Li)_sample/(⁷Li /⁶Li)_L-SVEC − 1]) with high δ⁷Li altered oceanic crusts can explain the MORB-like Li isotopic signature of arc lavas. However, marine sediments with low δ⁷Li values have rarely been reported. The metasomatism of metasedimentary rocks in mélange zones may induce large Li isotopic fractionation; however, the Li isotopic behaviour of metasedimentary rocks during high-temperature fluid-rock reactions remains poorly understood. In this study, an integrated Li-O-Sr-Nd isotopic investigation was conducted on the Baiyun orogenic gold deposit, which represents a relatively simplified high-T hydrothermal system, to explore the Li isotopic behaviour during high-T metasomatism (>200 °C) of metapelites. The main host rocks in Baiyun are lithologically monotonous schists, with alterations including K-feldspathization, sericitization, and carbonation. The Nd isotopes identified host rock samples that could best represent the protolith of the altered schists in Baiyun. The Sr and O isotopic modelling yielded consistent water/rock ratios of 0.1–7.6 and 0.6–5.9, respectively, suggesting that relatively small volumes of fluids were infiltrated. There is no correlation among Li, Sr, and O isotopes; instead, a negative Li-K₂O correlation and a positive δ⁷Li-K₂O correlation of the altered schists are observed, suggesting that potassic metasomatism controlled Li concentrations and Li isotopes. The δ⁷Li values of altered schists in Baiyun can be classified into Group I, having lower Li concentrations (3.2–22.2 ppm) and δ⁷Li values (−3.8–0.4‰) than the protolith (31.6–47.9 ppm, 0.9–2.8‰), and Group II, having significantly lower Li concentrations (0.9–2.5 ppm) and overlapped or higher δ⁷Li values (1.0–4.5‰) than the protolith. Fluid leaching during high-T alteration removes Li and more ⁷Li than ⁶Li, which accounts for the lower Li concentrations and δ⁷Li values of Group I. When there is little Li remaining in rocks owing to progressive fluid leaching, the Li isotopes of the altered schists are equilibrated with heavy fluid Li (fluid buffering), which leads to higher δ⁷Li values observed in Group II. Based on a case study in Baiyun, this study proposes that similar high-T metasomatism of metasedimentary rocks in mélange zones could result in low δ⁷Li sediment inputs. Mixing of flux-modified isotopically light sediment inputs with isotopically heavy, altered oceanic crusts could account for the MORB-like Li isotopes of arc lavas.

低 δ ⁷ Li 沉积物组分 (δ ⁷ Li(‰) = 1000 × [( ⁷ Li/ ⁶ Li)_样品/( ⁷ Li / ⁶ Li) _L-SVEC  - 1]) 与高 δ ⁷ Li 蚀变洋壳的混合可以解释弧熔岩的类似 MORB 的 Li 同位素特征。然而，具有低 δ ^{7的海洋沉积物}Li 值很少被报道。混杂带变沉积岩的交代作用可能导致大的Li同位素分馏；然而，在高温流体-岩石反应过程中，变沉积岩的锂同位素行为仍然知之甚少。本研究对代表相对简化的高T热液系统的白云造山金矿进行了综合 Li-O-Sr-Nd 同位素研究，以探索高T期间的 Li 同位素行为。Metapelites的交代作用（> 200°C）。白云主要围岩为岩性单调的片岩，具有钾长石化、绢云母化、碳化等蚀变。Nd同位素确定了最能代表白云蚀变片岩原岩的母岩样品。Sr 和 O 同位素模型分别产生一致的水/岩比，分别为 0.1-7.6 和 0.6-5.9，表明渗透的流体体积相对较小。Li、Sr和O同位素之间没有相关性；相反，观察到改变的片岩的负Li-K ₂ O相关和正δ ⁷ Li-K ₂ O相关，表明钾交代控制了Li浓度和Li同位素。δ ⁷白云蚀变片岩的 Li 值可分为 I ​​组，其 Li 浓度（3.2-22.2 ppm）和 δ ⁷ Li 值（-3.8-0.4‰）低于原岩（31.6-47.9 ppm，0.9-2.8‰）和第 II 组，与原石相比，Li 浓度显着降低（0.9-2.5 ppm）和重叠或更高的 δ ⁷ Li 值（1.0-4.5‰）。高T蚀变过程中的流体浸出去除了 Li 和⁷ Li 多于⁶ Li，这导致 I 组的 Li 浓度和 δ ⁷ Li 值较低。当由于进行性流体浸出而岩石中剩余的 Li 很少时，Li 同位素的改变的片岩与重流体 Li 平衡（流体缓冲），这导致更高的 δ⁷在第 II 组中观察到的 Li 值。基于白云的一个案例研究，本研究提出混杂带变沉积岩的类似高T交代作用可能导致低 δ ⁷ Li 沉积物输入。通量改性同位素轻沉积物输入与同位素重同位素改变的海洋地壳的混合可以解释弧熔岩的 MORB 类锂同位素。