Mercury (Hg) provides critical information on terrestrial planet formation and evolution due to its unique physicochemical properties and multiform isotopic compositions. Current knowledge of Hg is mainly limited to Earth's surface environments, and the understanding of Hg in the Earth's interior remains unclear. Accretionary orogens are major settings for continental crustal growth and crust-mantle interactions. We studied the Hg concentration and isotopic composition of igneous rocks in the eastern Central Asian orogenic belt, using Hg as a proxy to trace the recycling of surface materials in Earth's lithosphere. Our results show low Hg abundances in mafic through felsic igneous rocks (4.93 ± 4.35 ppb, standard deviation [SD], n = 267). Mafic rocks show slightly lower δ202Hg (−2.9‰ ± 0.5‰, SD, n = 24) than intermediate (−2.4‰ ± 0.8‰, SD, n = 58) and felsic (−1.5‰ ± 0.8‰, SD, n = 185) rocks, indicating a chemical stratification of Hg isotopic composition in the continental crust with isotopically lighter Hg in the lower part and heavier Hg in the upper part. Slightly positive Δ199Hg values are observed in mantle-derived mafic (0.07‰ ± 0.06‰, SD) and intermediate (0.06‰ ± 0.07‰, SD) rocks, which agree well with those reported for marine sediments, indicating the involvement of fluids or melts from the oceanic crust. Larger variations of Δ199Hg values (−0.26‰ to +0.21‰, average: 0.01‰ ± 0.08‰, SD, n = 185) are observed in felsic rocks, further indicating recycling of surface Hg from the marine reservoir via slab subduction (reflected by positive values) plus magmatic assimilation of terrestrial Hg (reflected by negative values). Our study demonstrates that Hg isotopes can be a promising tracer for the chemical dynamics of Earth's lithosphere.

中文翻译：

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增生造山带火成岩的汞同位素组成：对岩石圈再循环的影响

水星 (Hg) 因其独特的物理化学性质和多种同位素组成，提供了关于类地行星形成和演化的重要信息。目前对汞的认识主要局限于地球表面环境，对地球内部汞的认识仍不清楚。增生造山带是大陆地壳生长和壳幔相互作用的主要环境。我们研究了中亚造山带东部火成岩的汞浓度和同位素组成，以汞为代表来追踪地球岩石圈中地表物质的循环利用。我们的结果显示长英质火成岩中镁铁质中的 Hg 丰度较低（4.93 ± 4.35 ppb，标准偏差 [SD]，n = 267）。基性岩的 δ202Hg (-2.9‰ ± 0.5‰, SD, n = 24) 略低于中间 (-2.4‰ ± 0.8‰, SD, n = 58) 和长英质 (-1.5‰ ± 0.8‰, SD, n = 185) 岩石，表明大陆地壳中 Hg 同位素组成的化学分层，下部 Hg 同位素较轻，上部 Hg 较重部分。地幔基镁铁质（0.07‰±0.06‰，SD）和中间（0.06‰±0.07‰，SD）岩石中观察到微正的Δ199Hg值，与报道的海洋沉积物非常吻合，表明流体或熔体的参与来自大洋地壳。在长英质岩石中观察到 Δ199Hg 值的较大变化（-0.26‰ 至 +0.21‰，平均值：0.01‰ ± 0.08‰，SD，n = 185），进一步表明通过板片俯冲从海洋储层中回收地表汞（反映为正值）加上陆地汞的岩浆同化（由负值反映）。