At the Seridó Belt pegmatitic province, fluid advection from dykes and sills led to trace element diffusion and partitioning in biotite, producing sub metric concentration halos in host mica schist and gneiss. We analyzed trace element concentration vs. distance profiles in the host rock of pegmatitic granite intrusions showing enrichments in Li, F, Cl, Zn, Rb, Nb, Sn, Cs, Ta, U and depletions in Sr and Ba. We estimated fluid temperatures in the range 600 to 700 °C using methods of Ti in biotite, F-OH in biotite-apatite and Tschermak component in biotite-muscovite. We analytically modeled thermal profiles around pegmatitic planar intrusions and found that cooling by thermal flats in the first meters into the host rock is reached in 100 years for a 10 m thick sill. The model constraints sustained heat flow during pegmatitic melt emplacement into a colder host rock. The measured trace element profiles were fitted with solutions of differential equations modeling advection-diffusion-partitioning in porous media under isothermal and cooling conditions. Each trace element profile is equally fitted by values of pegmatitic fluid concentration vs. fluid flux duration plotting as a straight line. We obtained a theorical framework combining pegmatitic fluid trace element composition, fluid flux duration and velocity, rock/fluid trace element partition coefficient, and cooling rate. Using published fluid inclusion trace element composition, we obtained fluid flux duration between tens of years to several centuries for the studied profiles. In the case of low temperature fluid flux at 450 °C the modeled flux duration is increased by less than one order of magnitude. The results allow us to interpret the trace element halos as sub millennial hot isothermal fluid influx from the pegmatites into their host rock. Trace element partitioning from the fluid into host rock falls mostly within the range of 0.01 to 25 and decreases in the order Nb, Cu, Rb, Zn-Li, Cs-Sn. The model constraints fluid advection velocity between 1 × 10⁻¹¹ m/s and 1 × 10⁻⁹ m/s, typical of regional metamorphism to shear focused fluid flow regimes. The trace element enrichment of biotite along the profiles reproduces the observed pattern for whole rock, indicating that biotite is their main sink during pegmatitic fluid influx. Using experimental F in biotite diffusivity we obtained a minimal planar diffusion distance, or the effective porosity, between 7 and 15 μm for the total F re-homogenization of metamorphic biotite by pegmatitic fluid. As shown from others fluid-present petrogenetic systems, the trace element contents of biotite in host rock at the contact with pegmatitic intrusions can be a potential tool for the assessment of their rare metal potential.

在SeridóBelt的聚乙二醇化省，来自堤坝和窗台的流体平流导致黑云母中痕量元素的扩散和分配，从而在寄主云母片岩和片麻岩中产生亚度量浓度的光晕。我们分析了成岩花岗岩侵入体中的痕量元素浓度与距离分布的关系曲线，显示出富集于Li，F，Cl，Zn，Rb，Nb，Sn，Cs，Ta，U以及Sr和Ba的贫化。我们使用黑云母中的Ti，黑云母-磷灰石中的F-OH和黑云母-白云母中的Tschermak组分的方法估算了流体温度在600至700°C范围内。我们分析了围绕成象平面侵入体的热剖面模型，发现对于厚度为10 m的门槛，在100年内就可以通过热平面在进入主岩的前几米内达到冷却效果。该模型限制了将古卷熔体安置到较冷的主体岩石中的持续热流。在等温和冷却条件下，对测得的痕量元素分布图拟合微分方程的模型，该模型模拟了多孔介质中的对流-扩散-分配。每个痕量元素的分布图均以笔电流体浓度与流体通量持续时间的值绘制为一条直线。我们获得了一个理论框架，其结合了古卷流体微量元素组成，流体通量持续时间和速度，岩石/流体微量元素分配系数以及冷却速率。使用已公布的流体包裹体微量元素组成，对于所研究的剖面，我们获得了几十年到几个世纪之间的流体通量持续时间。在450°C的低温流体通量的情况下，模拟的通量持续时间增加不到一个数量级。结果使我们能够将微量元素晕解释为千年期热等温流体从伟晶岩流入其宿主岩石。从流体分配到基质岩中的痕量元素主要在0.01至25的范围内，并以Nb，Cu，Rb，Zn-Li，Cs-Sn的顺序减少。该模型将流体对流速度限制在1×10之间^-11 m / s和1×10 ^-9 m / s，典型的区域变质作用是剪切集中流体的流动状态。黑云母沿剖面的微量元素富集再现了整个岩石的观察模式，表明黑云母是它们在岩溶流体涌入期间的主要汇。使用黑云母扩散率中的实验性F，我们得出了变质黑云母通过凝析液重新进行F均质化的最小平面扩散距离，即有效孔隙率，介于7和15μm之间。从其他流体成岩系统中可以看出，与岩屑侵入体接触时，宿主岩中黑云母中的微量元素含量可能是评估其稀有金属潜力的潜在工具。