ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    阿尔金南缘苏满马勒央凝灰质角砾岩和构造角砾岩时代、成因及地质意义

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

    • 摘要: 苏满马勒央地区位于新疆且末县南部、东昆仑西段,因自然条件所限,前人对该区的研究主要依赖于区域地质填图,区内火山–沉积岩系的形成时代、成因及构造背景尚缺乏系统的构造变形解析、地质年代学和地球化学资料制约。笔者对该区含凝灰质角砾岩和构造角砾岩典型剖面开展了野外构造解析、岩相学观察、全岩主微量元素地球化学分析及 LA-ICP-MS 锆石 U-Pb 定年工作。野外构造解析表明,该剖面主要发育逆冲与走滑断裂叠加的脆性变形组合,反映阿尔金断裂带新生代左行走滑主导、局部挤压转换的变形特征。凝灰质火山角砾岩具典型的火山碎屑结构,基质为凝灰质;构造角砾岩则以强烈破碎、硅化及构造–热液叠加改造为主要特征。地球化学结果显示,岩石主要呈现富集大离子亲石元素(LILE)、亏损高场强元素(HFSE)、Sr 负异常等特征。稀土元素总量 ∑REE 值为 107×10–6~823×10–6,LREE/HREE值为2.04~4.17,呈轻稀土富集型配分模式,具中等 Eu 负异常(Eu/Eu*值为0.65~0.98)。Th/U 值为1.38~4.30,指示俯冲流体交代作用,整体显示陆缘弧地球化学亲缘性。凝灰质角砾岩与构造角砾岩中的锆石均属捕获成因的锆石,其U-Pb年龄跨越新太古代、古元古代、中元古代—新元古代及古生代等多个地质时期,并呈现5个年龄峰值(约 2.6 Ga、1.8 Ga、1.5 Ga、1.2 Ga及473 Ma)。上述年龄谱特征表明,源区曾先后混入多期基底物质并叠加构造–热事件产物。最年轻的473 Ma年龄组因锆石颗粒数较少,不宜直接解释为成岩年龄,仅作为最年轻年龄组,用以限定岩石的形成时代不早于约 473 Ma。综合研究认为,苏满马勒央地区凝灰质角砾岩与构造角砾岩原岩形成于与俯冲相关的陆缘弧环境,是原特提斯洋俯冲增生过程在东昆仑西段的岩石记录。此外,构造角砾岩内发育多期热液脉体与褐铁矿化蚀变,表明该区后期断裂带可能曾作为热液流体运移和沉淀的重要通道,对后续金矿找矿具有一定指示意义。

       

      Abstract: 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.

       

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