Abstract Paired LA-ICP-MS U Pb and Lu Hf isotopic data and trace element data are reported on zircon in thin section from poorly known acid migmatites exposed in the Cabo Ortegal Complex, Western Variscides, NW Spain. The migmatites are part of the high-pressure granulite unit, tectonically placed between the eclogite and ultramafic units. Large oscillatory zoned zircon cores date the felsic igneous protolith at 459 ± 7 Ma as a minimum age reflecting a protracted basic magma differentiation in a Cambro-Ordovician arc setting. Lower Th/U, weakly- to un-zoned overgrowth rims are attributed to partial melting at 392 ± 5 Ma during high-pressure metamorphism. The distinctly lower epsilon Hf (+4.0) of the rim relative to the core (+8.2) implies an open-system behavior metamorphism and mass transfer between different units in deep parts of a subduction channel during the Variscan Orogeny. Tiny xenomorphic zircon crystals devoid of internal microstructures dated at 355 ± 4 Ma and with nearly flat REE patterns are interpreted as product of metamorphic overprint driven by hot fluids. The latter is envisaged as a subduction channel short-duration metamorphic phenomenon.

中文翻译：

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来自 Cabo Ortegal 杂岩体（西班牙西北部）的高压酸性混合岩的 U-Pb、Hf 同位素和 REE 限制：Variscan 俯冲通道中短期变质作用的新证据

摘要 LA-ICP-MS 的 U Pb 和 Lu Hf 配对同位素数据和痕量元素数据报告了来自西班牙西北部 Cabo Ortegal 杂岩中的鲜为人知的酸性混合岩的锆石薄片。混合岩是高压麻粒岩单元的一部分，在构造上位于榴辉岩和超基性单元之间。大型振荡带状锆石核将长英质火成岩原岩的年龄确定为 459 ± 7 Ma，作为反映寒武纪-奥陶纪弧环境中长期基本岩浆分化的最小年龄。较低的 Th/U，弱到未分区的过度生长边缘归因于高压变质作用期间 392 ± 5 Ma 的部分熔化。边缘相对于核心 (+8.0) 明显较低的 epsilon Hf (+4.0)。2) 暗示了瓦里斯坎造山运动期间俯冲通道深部不同单元之间的开放系统行为变质和质量传递。没有内部微结构的微小异形锆石晶体的年代为 355 ± 4 Ma，并且具有几乎平坦的 REE 图案，被解释为由热流体驱动的变质叠印产物。后者被设想为俯冲通道短时变质现象。