Development of new oxybarometers for silicic magmas

中-硅质岩浆的氧逸度通常是用Fe-Ti双氧化物温压计法重建的。然而，许多硅质火成岩缺乏共存的磁铁矿和钛铁矿或其他可以用来限制氧气的镁铁质矿物。此外，在许多最初存在这种相的样品中，它们随后在固相线下过程中被破坏或重新设置。该项目的目的是开发三种新的矿物熔融分配式氧气压计，既适用于火山岩，也适用于缓慢冷却的侵入岩。该项目分为三个独立的子项目，涉及三种不同多价元素的矿物熔体分配：(1)钒在磁铁矿和硅酸盐熔体之间的分配，(2)铀在锆石(或磷灰石)和硅酸盐熔体之间的分配，以及(3)铁在长石和硅酸盐熔体之间的分配。这些平衡中的每一个都将在受控的温度和fO2条件下进行实验研究，所产生的校准将在已知T-fO2条件下形成的自然样品上进行测试。后者将通过对岩浆石英斑晶中的硅酸盐熔融包裹体和固体包裹体进行激光烧蚀电感耦合等离子体质谱分析来完成，其优点是捕获的相受到热液的保护而不被改变，在岩浆冷却过程中包裹体内发生的再平衡过程在分析整个未暴露的包裹体时被“逆转”。

The oxygen fugacity of intermediate to silicic magmas is most commonly reconstructed by Fe-Ti two-oxide thermobarometry. However, many silicic igneous rocks lack coexisting magnetite and ilmenite or other mafic minerals that could be used to constrain fO2. Furthermore, in many samples in which such phases originally were present they subsequently were destroyed or reset during subsolidus processes. The aim of this project is to develop three new mineral-melt partitioning oxybarometers that can be applied to both volcanic and slowly-cooled, intrusive rocks. The project is divided into three independent subprojects that deal with the mineral-melt partitioning of three different multivalent elements: (1) vanadium partitioning between magnetite and silicate melt, (2) uranium partitioning between zircon (or apatite) and silicate melt, and (3) iron partitioning between feldspar and silicate melt. Each of these equilibria will be investigated experimentally under controlled temperature and fO2 conditions, and the resulting calibrations will be tested on natural samples that formed at known T-fO2 conditions. The latter will be done via laser ablation ICP-MS analysis of silicate melt inclusions and solid inclusions within magmatic quartz phenocrysts, which has the advantage that the trapped phases were protected from alteration by hydrothermal fluids, and that re-equilibration processes that occurred within the inclusions during magma cooling are "reversed" during the analysis of entire, unexposed inclusions.