Experimental determination of boron isotope fractionation between silicate melts and aqueous fluids, with application to understanding magmatic-hydrothermal ore genesis

这一建议将解决理解与花岗岩和伟晶岩有关的矿床形成的一个关键空白：岩浆-热液转变的作用是什么？理论预测，在这种转变过程中，硼同位素应该在硅酸盐熔体和流体之间发生分馏，经验研究表明，电气石可以在天然岩石中记录这种转变。然而，验证这一点所需的信息是缺乏的，因为目前对花岗岩熔体和源自它们的含水流体之间的b同位素分馏程度没有一致意见。本文提出的研究旨在解决这一问题，通过实验研究在自然系统中具有现实意义的可变成分和可控压力-温度条件下流体与合成花岗岩熔体之间的b同位素交换。研究将包括：a)用SIMS b -同位素谱测试时间序列实验，以确定平衡交换的实现；b)用TIMS对淬火熔体和流体进行b -同位素分析；c)用核磁共振光谱确定成分可变的合成熔体中硼的配位数；d)用熔体和流体相中硼形态的分子动力学模拟来补充实验工作。将结果应用于自然成矿系统，将通过重新解释来自波茨坦SIMS实验室和其他已发表来源的花岗岩和伟晶岩相关矿床的b同位素变化研究的丰富现有数据来完成，其中电气石被怀疑是在岩浆-热液转变中结晶的。

This proposal will address a critical gap of understanding the formation of ore deposits related to granites and pegmatites: what is the role of the magmatic-hydrothermal transition? Theory predicts that boron isotopes should fractionate between silicate melt and fluid at this transition, and empirical studies suggest that tourmaline can record this shift in natural rocks. However, the information needed to validate this is lacking because there is no current agreement on the extent of B-isotope fractionation between granitic melts and aqueous fluids derived from them. The research proposed here aims to resolve this question by conducting experimental studies of B-isotope exchange between fluids and synthetic granitic melts with variable compositions and controlled pressure-temperature conditions that are realistic for natural systems. The investigations will include: a) time-series experiments tested with SIMS B-isotope profiling to establish attainment of equilibrium exchange, b) B-isotopic analysis of quenched melt and fluid by TIMS, c) determining the coordination number of boron in compositionally variable synthetic melts using NMR spectroscopy and d) complementing the experimental work with molecular dynamic simulations of boron speciation in melt and fluid phases. Application of the results to natural ore-forming systems will be done by re-interpreting the abundant existing data from studies of B-isotope variations in granite- and pegmatite-related ore deposits from the Potsdam SIMS laboratory and other published sources, where tourmaline was suspected to have crystallized across the magmatic-hydrothermal transition.