Biotite Equilibria in High Silica Rhyolites: Controls on Volatile Fugacities and Abundance in Bishop and Toba Tuff Magmas

9526527卢瑟福，拟议的研究是确定高硅流纹岩的相平衡，从控制黑云母组成和黑云母稳定性开始。黑云母-碱性长石-磁铁矿平衡是确定喷发前水逸度的一种强有力的工具，但由于黑云母的铁和亚铁组成随压力、温度和流体组成的约束很差，所以使用有限。将进行两组实验：(1)用碱性长石和含钛磁铁矿对黑云母进行退火；(2)在毕晓普凝灰岩和托巴凝灰岩样品上进行水热实验，所有实验都是在混合流体(H2O、CO2、F)的存在下进行的。用微量滴定和显微x射线光电子能谱测定黑云母的铁/铁组成。用离子探针和电子探针分别测定O、H和F的含量。这项研究将约束高硅流纹岩中黑云母的稳定性和成分，标定黑云母-磁铁矿-碱性长石平衡，并将这些结果应用于确定毕晓普和托巴岩浆的喷发前条件。

9526527 Rutherford The proposed research is to determine the phase equilibria for high silica rhyolite beginning with the controls on biotite composition and biotite stability. The biotite-alkali feldspar-magnetite equilibrium is potentially a powerful tool for determining the pre-eruptive water fugacities, but has been of limited use because of the poor constraints on the ferric and ferrous iron composition of biotite as a function of pressure, temperature, and fluid composition. Two sets of experiments will be performed: (1) annealing biotite with alkali feldspar and titaniferous magnetite, and (2) hydrothermal experiments on samples from the Bishop and Toba Tuffs, all in the presence of mixed fluids (H2O, CO2 , F) of controlled composition. The ferrous/ferric composition of biotite will be determined by microtitration and micro x-ray photoelectron spectroscopy. The O, H and F contents will be determined by ion probe and electron microprobe. This research will constrain the stability and composition of biotite in high silica rhyolite, calibrate the biotite-magnetite-alkali feldspar equilibrium, and apply these results to determine the pre-eruptive conditions of the Bishop and Toba magmas.