Phase equilibria of a Be, U and F-enriched vitrophyre from Spor Mountain, Utah
Phase equilibria of a Be, U and F-enriched vitrophyre from Spor Mountain, Utah
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DOI：
10.1016/0016-7037(87)90057-3
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发表时间：
1987-03
影响因子：
5
通讯作者：
J. Webster;J. Holloway;R. Hervig
中科院分区：
文献类型：
--
作者：
J. Webster;J. Holloway;R. Hervig
为了确定黄玉流纹岩岩浆的喷发前温度和H2O含量，实验测定了以黄玉流纹岩为代表的玻璃斑岩的平衡熔融关系。玻璃斑岩样品富含F和不相容元素，由约70%未蚀变的火山玻璃和30%的黑云母、石英、辉长岩、斜长石、岩浆萤石和各种副相晶体组成。黑云母的稳定性强烈地依赖于温度、压力和熔体中的H2O，而且显然与本研究范围内ƒO2的变化无关。在饱和水熔体中，随着压力从1 2 kbar增加到2 kbar，黑云母的热稳定性相对于石英、闪锌矿和斜长石的热稳定性增强。萤石在黑云母稳定性曲线的50°C以下但在50°C至75°C范围内稳定，在所研究的所有流体条件下，黄玉存在于固相线及其附近的产物中。玻璃斑岩中的1.2wt.%F导致在所研究的所有流体条件下，固相线温度都非常低，为≤525℃。实验测定的玻璃斑岩结晶序列与观察到的玻璃斑岩和上覆黄玉流纹岩的结晶序列对比表明，玻璃斑岩和黄玉流纹岩中的斑晶在1kb的压力下结晶，黑云母初始结晶时岩浆中至少含有4wt.%的水，岩浆中含有5wt.%的喷发前水。
The equilibrium melting relations of a vitrophyre representative of topaz rhyolites have been experimentally determined in order to constrain the pre-eruption temperature and H 2 O content of topaz rhyolite magmas. The vitrophyre sample is strongly enriched in F and incompatible elements and consists of approximately 70% unaltered volcanic glass and 30% crystals of biotite, quartz, sanidine, plagioclase, magmatic fluorite and a variety of accessory phases. Biotite stability is strongly dependent on temperature, pressure, and a H 2 O, in the melt, and is apparently independent of the variations in ƒo 2 over the range investigated in this study. The thermal stability of biotite increases relative to that of quartz, sanidine, and plagioclase in water-saturated melts as pressure increases from 1 2 to 2 kbar. Fluorite is stable to temperatures below but within 50° to 75° C of the biotite stability curve, and topaz is present in the products of runs at and near the solidus for all fluid conditions investigated. The 1.2 wt.% F in the vitrophyre results in very low solidus temperatures of≤ 525° C for all fluid conditions studied. Comparison of the experimentally determined crystallization sequence of the vitrophyre with the observed crystallization sequence of the vitrophyre and of the overlying topaz rhyolites indicates that the phenocrysts in the vitrophyre and in the topaz rhyolites crystallized at a pressure≥ 1 kb, that the magma contained at least 4 wt.% water during initial crystallization of biotite, and that the magma contained a pre-eruption water content of 5 wt.%.