High-Mg andesites (HMAs) and their cognate intrusive rocks constitute volumetrically very small proportions of the total earth, and are mainly distributed along the edges of convergent plates. Petrogenetic studies can provide possible solutions for discrepancies in the geodynamics and subduction zone evolution. This paper presents the first ever reports of the newly discovered high-Mg diorite in Akechukesai area, the western part of the East Kunlun Orogenic Belt, and provides a reference for the evolutionary history and subduction mechanism of the Proto-Tethys Ocean. Akechukesai high-Mg diorites yielded a weighted mean zircon U-Pb dating age of 427.3 ± 2.3 Ma (Middle Silurian). Results of the geochemical analyses show that the high-Mg diorites were high-K calc-alkaline series with the SiO₂ content ranging 50.40 to 55.41 wt%. They are characterized by high values of Mg^# (67–77), high MgO (6.92–10.58 wt%), TiO₂ (0.53–0.87 wt%), Cr (286–615 ppm), Ni (61–124 ppm), Ba (570–927 ppm) contents, and low FeO^total/MgO ratios (0.54–0.89). Furthermore, they exhibit nearly flat right-declined rare-earth element (REE) patterns with slight LREE enrichment. The samples are enriched in large ion lithophile elements (e.g., Ba, Rb, and Th) and depleted in high field strength elements (e.g., Ta, Nb, and Ti). These geochemical features are analogous to the sanukitic high-Mg andesites. The mean value of the initial ε_Hf(t) is −1.3, indicating that the source is enriched mantle. The values of Rb/Cs, Ba/La, and La/Sm ratios suggest that subducting sediments formed an important component of the magmatic source. The presence of water-bearing minerals such as amphibole and biotite indicate a water-rich and oxygen-rich primitive magma system. Petrogenetic analysis indicates that the Akechukesai high-Mg diorites probably formed by melts and aqueous fluids produced from partial melting of the subducting sediments interacting with mantle peridotites. We hypothesize that, after the closure of the Proto-Tethys Ocean Basin in the Middle Silurian, the deep subducted slab broke-off and formed a slab window, asthenospheric material upwelled heating the subducting sediments and causing them to melt. Thus, we suggest that the emplacement of the Akechukesai high-Mg diorites mark the commencement of post-collisional magmatism.

高镁安山岩 (HMA) 及其同类侵入岩在地球总量中所占的比例很小，主要分布在会聚板块的边缘。岩石成因研究可以为地球动力学和俯冲带演化中的差异提供可能的解决方案。本文首次报道了东昆仑造山带西部阿克楚克赛地区新发现的高镁闪长岩，为原始特提斯洋的演化历史和俯冲机制提供了参考。阿克楚克赛高镁闪长岩的加权平均锆石 U-Pb 定年年龄为 427.3 ± 2.3 Ma（中志留纪）。地球化学分析结果表明，高镁闪长岩为高钾钙碱性系列，SiO ₂含量范围为 50.40 至 55.41 wt%。它们的特点是高 Mg ^# (67–77)、高 MgO (6.92–10.58 wt%)、TiO ₂ (0.53–0.87 wt%)、Cr (286–615 ppm)、Ni (61–124 ppm) , Ba (570–927 ppm) 含量和低 FeO^总/MgO 比率 (0.54–0.89)。此外，它们表现出几乎平坦的右倾稀土元素 (REE) 模式，并具有轻微的 LREE 富集。样品富含大离子亲石元素（例如，Ba、Rb 和 Th）并缺乏高场强元素（例如，Ta、Nb 和 Ti）。这些地球化学特征类似于sanukitic高镁安山岩。初始ε _Hf的平均值(t) 为-1.3，说明来源为富集地幔。Rb/Cs、Ba/La 和 La/Sm 比值表明俯冲沉积物是岩浆源的重要组成部分。角闪石和黑云母等含水矿物的存在表明原始岩浆系统富水富氧。岩石成因分析表明，阿克楚克赛高镁闪长岩可能由俯冲沉积物与地幔橄榄岩相互作用产生的部分熔融产生的熔体和含水流体形成。我们假设，在中志留纪原始特提斯洋盆地关闭后，深俯冲板块断裂并形成板块窗口，软流圈物质上涌加热俯冲沉积物并使其熔化。因此，