Geochronology, Genesis, and Geological Significance of Tuffaceous Breccia and Tectonic Breccia at Sumaomaleyang on the Southern Margin of the Altyn Tagh

The Suman Maleyang area is located in southern Qiemo County, Xinjiang, in the western East Kunlun. Owing to its remote setting and difficult field conditions, previous work has relied largely on regional geological mapping, and the age, origin, and tectonic setting of the volcanic-sedimentary succession remain poorly constrained by structural, geochronological, and geochemical data. Here we investigate a representative section containing tuffaceous volcanic breccia and tectonic breccia through field structural analysis, petrography, whole-rock major- and trace-element geochemistry, and LA-ICP-MS zircon U-Pb dating. Field observations reveal brittle deformation characterized by superposed thrust and strike-slip faulting, consistent with Cenozoic deformation along the Altyn Tagh fault system dominated by sinistral strike-slip motion with local transpression. The tuffaceous volcanic breccia preserves typical volcaniclastic textures with a tuffaceous matrix, whereas the tectonic breccia is characterized by intense fragmentation, silicification, and tectono-hydrothermal overprinting. Geochemically, the rocks are enriched in large-ion lithophile elements, depleted in high-field-strength elements, and show negative Sr anomalies. They have total REE contents of 107×10^–6–823×10^–6, LREE/HREE ratios of 2.04–4.17, LREE-enriched patterns, and moderate negative Eu anomalies (Eu/Eu*=0.65–0.98). Th/U ratios range from 1.38 to 4.30, and the overall trace-element characteristics show an affinity with a subduction-related continental-margin arc setting. Zircon U-Pb ages span the Neoarchean, Paleoproterozoic, Mesoproterozoic–Neoproterozoic, and Paleozoic, with prominent age populations at ca. 2.6 Ga, 1.8 Ga, 1.5 Ga, 1.2 Ga, and 473 Ma. The zircons are dominated by xenocrystic grains and record repeated contributions from older basement components and multiple regional tectonothermal events. The youngest population at ca. 473 Ma contains only a few grains and is therefore not interpreted as a robust crystallization age; instead, it constrains the maximum depositional age to ca. 473 Ma. Taken together, the petrographic and geochemical characteristics of the tuffaceous volcanic breccia suggest formation in a subduction-related continental-margin arc setting associated with Proto-Tethyan subduction and accretion in the western East Kunlun. The tectonic breccia was subsequently generated by fault-related fragmentation and hydrothermal alteration of the volcanic rocks. Multistage hydrothermal veins and limonitic alteration within the fault zones further suggest that these structures may have acted as pathways for hydrothermal fluid migration and precipitation, with potential implications for gold exploration in the area.