Collaborative Research: Measurement of Copper Speciation in Basaltic Glasses using X-ray Absorption Spectroscopy, a New Window on Metal Solubility and Transport in Magmatic Systems

金属（如铜）在硅酸盐熔体中的溶解度会受到岩浆的自然性质（如压力、温度和熔体成分）的强烈影响。了解这些物质如何控制金属的溶解度，特别是铜的溶解度，有很多重要的原因。它有助于研究人员了解类地行星核心形成的潜在驱动机制，或者导致经济上重要的成矿矿床形成的条件。这也是了解火山脱气如何影响金属排放到大气中的关键。本研究提出使用基于同步加速器的x射线吸收精细结构（XAFS）光谱分析天然和合成岩浆玻璃，目的是为陆地熔体中Cu的形态提供第一个直接的实验约束。XAFS是目前唯一可用于直接测量自然浓度下岩浆玻璃中Cu形态的高空间分辨率方法。除了限制熔体中存在哪些Cu物种的科学目标外，这项工作还将扩大少数民族学生对地球科学的参与，并培养学生掌握最先进的实验和分析技术。这将通过三个重叠的项目来实现。项目1将包括在控制硫和氧条件下生产的合成玄武岩玻璃的铜形态测量。这套合成玻璃将仔细控制氧和硫逸度，然后使用XAFS分析铜形态的变化。项目2包括从火山系统中取样的天然玻璃的铜形态测量。该项目的目标是来自硫化物占主导的低h2o熔体系统的自然样品（使用从2008年至今的基拉韦厄山顶喷口收集的样品），来自硫化物占主导的高h2o熔体系统的样品（来自南喀斯喀特山脉的玄武岩煤渣锥体），以及来自南喀斯喀特山脉和墨西哥西部科利马地堑的硫酸盐占主导的火山样品。项目3将专注于开发先进的基于同步加速器的岩浆玻璃Cu K-edge XAFS光谱技术，该技术将应用于项目1和项目2的样品，重点是开发高能量分辨率荧光检测XAFS （HERFD-XAFS）技术，用于分析地质材料和岩浆玻璃中的Cu。与传统的XAFS方法相比，这种新的HERFD-XAFS技术有望提供更好的光谱灵敏度和分辨率，以独特地限制这些样品中存在的铜配体。这些建议的测量将是这些方法在岩浆玻璃上的首次应用，并将建立一个新的光谱测量数据库，供岩石学界使用。总之，这一系列研究将大大有助于我们对岩浆系统中金属溶解度和运输的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The solubility of metals such as copper (Cu) in silicate melts can be strongly influenced by natural properties of the magma such as pressure, temperature, and melt composition. Understanding how such things control metal solubility, particularly for Cu, is important for a number of reasons. It helps researchers understand potential driving mechanisms for core formation in terrestrial planets, or the conditions that lead to the formation of economically important metallogenic ore deposits. It's also key to understanding how volcanic degassing may impact metal emissions to the atmosphere. This study proposes to use synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy of natural and synthetic magmatic glasses with the goal of providing the first direct, experimental constraints on the speciation of Cu in terrestrial melts. XAFS is currently the only methodology available for directly measuring Cu speciation in magmatic glasses at natural concentrations with high spatial resolution. In addition to the scientific goal of constraining which Cu species exist in melts, this work will broaden the participation of minority students in geoscience, and train students in state-of-the-art experimental and analytical techniques.This will be achieved through three overlapping projects. Project 1 will include copper speciation measurements of synthetic basaltic glasses that are produced at controlled sulfur and oxygen conditions. This suite of synthetic glasses will have both oxygen and sulfur fugacity carefully controlled and will then be analyzed for changes in Cu speciation using XAFS. Project 2 includes Cu speciation measurements of natural glasses sampled from volcanic systems. This project targets natural samples from a sulfide-dominated system with H2O-poor melts (using samples collected from the Kilauea summit vent between 2008 and present), samples from a sulfide-dominated system with higher-H2O melts (from a basaltic cinder cone in the southern Cascade Range), and from sulfate dominated volcanics from both the southern Cascades Range and the Colima Graben in western Mexico. Project 3 will focus on developing advanced, synchrotron-based spectroscopic techniques for Cu K-edge XAFS of magmatic glasses, which will be applied to samples available from Projects 1 and 2, with a focus on developing High Energy-Resolution Fluorescence Detected XAFS (HERFD-XAFS) techniques for the analysis of Cu in geologic materials and magmatic glasses specifically. Such new HERFD-XAFS techniques hold the promise of providing superior spectroscopic sensitivity and resolution compared to conventional XAFS methods for uniquely constraining the copper ligands are present in these samples. These proposed measurements will be the first application of these methods to magmatic glasses and will establish a new database of spectroscopic measurements that will be available to the petrology community. Together, this suite of studies will significantly contribute to our understanding of metal solubility and transport in magmatic systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.