| 秘鲁南部海岸岩基带基底杂岩的锆石U-Pb年龄和Lu-Hf同位素约束 |
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| 引用本文：刘君安,郭维民,曾勇,Ccallo WALTER,Soberon DANTE,Santos ALAN.2026.秘鲁南部海岸岩基带基底杂岩的锆石U-Pb年龄和Lu-Hf同位素约束[J].地球学报,47(5):1117-1132. |
| DOI：10.3975/cagsb.2026.012721 |
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| 基金项目:本文由国家重点研发计划项目(编号: 2021YFC2901804)和中国地质调查局地质调查项目(编号: DD20230900702; DD202309007; DD20230051)联合资助。 |
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| 中文摘要:秘鲁阿雷基帕省海岸岩基带的基底杂岩是南美安第斯山中新生代造山带根部地壳的独特构成部分, 也是探究南美大陆早期演化的关键构造岩石单元。对其岩石组成与构造变形的调查研究不足, 且缺乏高精度年龄证据支撑, 已成为制约其构造演化认知的瓶颈。通过Atico–Chala地区的地质调查, 查明基底杂岩由表壳岩系和变质深成岩组成, 它经历了韧性剪切变形以及角闪岩相-麻粒岩相的变质作用。在表壳岩系中发现了层状斜长角闪片麻岩, 经岩石学、地球化学、锆石U-Pb年龄和Lu-Hf同位素研究, 厘定了其原岩为细碧岩类的基性火山熔岩, 归属于岛弧拉斑玄武岩或洋岛火山岩, 具有与大洋板片俯冲作用相关的富铌玄武岩地球化学特征。用LA-ICP-MS测得斜长角闪片麻岩的锆石U-Pb年龄为(1 863±8) Ma, 并经历(1 798±58) Ma的首次变质改造; εHf(t)的变化范围为–0.7~4.3, 亏损地幔二阶段模式年龄TDM2介于2 196~2 467 Ma, 表明其母岩浆主要源自深部幔源组分的部分熔融, 成岩过程中混入了很少量的古老地壳物质。研究显示, 该基底杂岩形成于古元古代造山纪末期(约1.86 Ga), 处于Nena古大陆东部的陆缘弧或洋岛环境, 深部大洋板块俯冲引发软流圈地幔上涌, 与岛弧下方的地幔楔混合喷发富铌玄武岩, 并在古元古代固结纪初期(约1.79 Ga)经历首次变质改造成为古元古代的火山杂岩, 是哥伦比亚超大陆聚合形成过程中本区残遗的重要证据。 |
| 中文关键词:基底杂岩 斜长角闪片麻岩 锆石U-Pb 锆石Lu-Hf同位素 LA-ICP-MS 哥伦比亚超大陆 海岸岩基带 秘鲁 |
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| Zircon U-Pb Geochronology and Lu-Hf Isotope Constraints of the Basement Complex in the Coastal Batholith, Southern Peru |
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| Abstract:The basement complex of the coastal batholith in Arequipa Province, Peru, is a unique crustal component at the root of the Neogene orogenic belt in the South American Andes. It is a critical tectonic rock unit for understanding the early evolution of the continent. However, its rock composition, tectonic deformation, and high-precision geochronology remain unclear. This has become a significant obstacle in fully comprehending its tectonic history. Detailed geological investigations conducted in the Atico–Chala region revealed that the basement gneiss consists of supracrust and metamorphic plutons. These rocks experienced ductile shear deformation and amphibolite-to-granulite facies metamorphism. Layered plagioclase-hornblende gneisses have been identified in supracrust. Integrated petrological, geochemical, zircon U-Pb geochronological, and Lu-Hf isotopic analyses indicated that the protolith corresponded to fine-basaltic volcanic lava classified as either island arc tholeiitic or oceanic island basalt. This classification aligns with geochemical signatures indicative of subduction-related processes, specifically Nb-enriched basalts associated with oceanic plate subduction. LA-ICP-MS U-Pb zircon dating yielded a crystallization age of (1 863±8) Ma for the plagioclase amphibolite gneiss, followed by an initial metamorphic event at (1 798±58) Ma. The εHf(t) values ranged from –0.7 to 4.3, whereas the two-stage depleted mantle model ages (TDM2) varied between 2 196 and 2 467 Ma. These results suggest that the parent magma originated primarily from the partial melting of deep mantle components, with minor contributions from ancient crustal materials during magmatism. This study indicates that the basement gneiss formed during the Late Paleoproterozoic orogeny (~1.86 Ga), likely in a continental margin arc or oceanic island setting on the eastern edge of the Nena supercontinent. Subduction of the oceanic lithosphere beneath this region triggered asthenospheric upwelling, leading to mixing with the depleted mantle wedge beneath the island arc and the subsequent eruption of Nb-rich basalt. The first metamorphic transformation occurred during the Early Paleoproterozoic consolidation period (~1.79 Ga), leading to the formation of Paleoproterozoic volcanic complexes. These geological features provide critical evidence for the preservation of tectonic remnants associated with the assembly of the Columbia supercontinent. |
| keywords:basement complex plagioclase amphibole gneiss zircon U-Pb geochronology zircon Lu-Hf isotopes LA-ICP-MS Columbia supercontinent coastal batholith Peru |
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