The behavior of Ti-Nb-Ta is crucial to reveal the genesis of island arc magmatism. However, mobilization and fractionation of Ti-Nb-Ta in subduction zone settings remain poorly understood. The discovery of felsic veins rich in coarse-grained rutile within retrograde eclogite of the North Qaidam UHP metamorphic belt provides a unique and novel opportunity to study age variation during rutile formation and alteration, as well as Ti-Nb-Ta mobility and fractionation during fluid/melt-rock interaction. Rutile high-resolution elemental mapping, and U-Pb bulk grain (ID-TIMS), and in-situ U-Pb geochronology have been utilized to focus on the properties of rutile in both, felsic vein and retrograde eclogite host to gain insight into possible similarities and differences. Three groups of rutile were distinguished according to its host rock, trace elements signature, and genetical connection to ilmenite: eclogite-hosted rutile (Rt-1), felsic vein-hosted rutile not associated with ilmenite (Rt-2a), and associated with ilmenite (Rt-2b). Field evidence and rutile trace elements characteristics document the source of vein-hosted rutile to be mainly derived from the eclogite during fluid/melt-rock interaction. Principal Component Analysis reveals that Nb, Ta, Sn, and W are more enriched in Rt-2a compared to Rt-1; Rt-2b has higher Nb, U, and Hf than Rt-2a. High-resolution mapping across large rutile grains shows the enrichment of high field strength elements (HFSEs) in rutile near to ilmenite, which indicates a HFSEs back diffusion from the rutile–ilmenite boundary during the replacement of rutile by ilmenite. The Nb/Ta ratios of Rt-2a are lower than those of Rt-1, which result from different partition coefficients of Nb and Ta during fluid/melt-rock interaction. The diffusion-influenced rutile exhibits suprachondritic Nb/Ta ratios and demonstrates that diffusion of Nb in rutile is higher than that of Ta under identical P-T conditions. Rutiles Rt-1 and Rt-2a yield consistent ²⁰⁶Pb/²³⁸U ages of 426-423 Ma, which is similar to the 433 ± 3 Ma determined by ID-TIMS results of bulk rutile grains. This indicates that Ti-Nb-Ta must have been mobilized during the exhumation of deeply subducted continental crust. However, the diffusion-influenced rutile shows a large variation of ages compared to the rutile not associated with ilmenite, demonstrating that the back-diffusion may affect the U-Pb system in rutile. Therefore, when rutile is partially altered into ilmenite or titanite, its dating should be used with caution. Thus, this study demonstrates volume diffusion is a very important geological process to result in extreme HFSEs fractionation and age variation of rutile on the mineral scale. The rutile aggerates that occur in the felsic veins in 3-5m distance to the adjacent retrograde eclogite suggest that Ti-Nb-Ta-rich melts/fluids were transported over a distance of at least several meters and that rutile does not represent a residual phase of the Na-Si-Al-, F- and CH₄-bearing fluid/melt environment that formed during anatexis of the subducted continental crust. The formation of rutile-rich aggregates during the generation, transport, and crystallization of subducted continental crust-derived melts/fluids in the deep roots of orogenic belts may be a critical trigger for the depletion of HFSEs in arc magmatic rocks during the formation of the continental crust.

Ti-Nb-Ta 的行为对于揭示岛弧岩浆作用的成因至关重要。然而，对俯冲带环境中 Ti-Nb-Ta 的动员和分馏仍然知之甚少。在柴北缘超高压变质带逆行榴辉岩中发现富含粗粒金红石的长英质脉，为研究金红石形成和蚀变过程中的年龄变化以及流体过程中Ti-Nb-Ta的迁移和分馏提供了独特而新颖的机会/熔岩相互作用。金红石高分辨率元素映射、U-Pb 散装颗粒 (ID-TIMS) 和原位 U-Pb 年代学已被用于关注长英质脉和逆行榴辉岩宿主中金红石的性质，以深入了解可能的相同点和不同点。金红石按其主岩分为三组，微量元素特征以及与钛铁矿的遗传联系：榴辉岩承载的金红石 (Rt-1)、长英质脉承载的金红石与钛铁矿无关 (Rt-2a)，以及与钛铁矿相关联 (Rt-2b)。现场证据和金红石微量元素特征证明脉状金红石的来源主要来自流体/熔岩相互作用过程中的榴辉岩。主成分分析表明，与 Rt-1 相比，Nb、Ta、Sn 和 W 在 Rt-2a 中的含量更高；Rt-2b 具有比 Rt-2a 更高的 Nb、U 和 Hf。大金红石晶粒的高分辨率映射显示钛铁矿附近金红石中高场强元素 (HFSEs) 的富集，这表明在钛铁矿取代金红石期间，HFSEs 从金红石-钛铁矿边界反向扩散。Rt-2a 的 Nb/Ta 比低于 Rt-1，这是由于流体/熔岩相互作用过程中 Nb 和 Ta 的分配系数不同造成的。受扩散影响的金红石表现出超球粒状 Nb/Ta 比率，并表明在相同的 PT 条件下，Nb 在金红石中的扩散高于 Ta。金红石 Rt-1 和 Rt-2a 产量一致²⁰⁶铅/ ²³⁸U 年龄为 426-423 Ma，与大块金红石晶粒的 ID-TIMS 结果确定的 433 ± 3 Ma 相似。这表明，在深俯冲大陆地壳的折返过程中，Ti-Nb-Ta 必定被动员起来。然而，与与钛铁矿无关的金红石相比，受扩散影响的金红石显示出较大的年龄变化，表明反向扩散可能影响金红石中的 U-Pb 系统。因此，当金红石部分转变为钛铁矿或钛铁矿时，应谨慎使用其测年。因此，这项研究表明，体积扩散是一个非常重要的地质过程，会导致矿物尺度上金红石的极端 HFSE 分馏和年龄变化。₄ - 在俯冲大陆地壳的深熔区形成的含流体/熔体环境。在造山带深部俯冲大陆地壳熔体/流体的生成、运输和结晶过程中，富含金红石的聚集体的形成可能是弧形岩浆岩中HFSEs在形成过程中耗尽的关键触发因素。大陆地壳。