Distribution and Origin of Gas and Volatiles in the Bishop Magma

火山斑晶中的玻璃包裹体可以揭示岩浆喷发前的状态及其结晶压力。这些知识对于了解火山喷发以及岩浆和矿石的形成和演化是必要的。该项目将确定单个浮石块的孔洞和晶体含量，以及斑晶的组成和玻璃包裹体中H2O和CO2的浓度，这些包裹体来自加利福尼亚州流纹岩毕晓普凝灰岩中受地层控制的地点的石英和长石斑晶。这些测定将被用来评估以下假设：1)在喷发前的岩浆体上部存在气体聚集，2)气体聚集主要是导致整体岩浆密度强烈向上降低，从而阻止对流和喷发期间岩浆分带的存活；3)从脉状喷发向火山灰流型喷发的转变对应着天然气聚集量的急剧变化；4)天然气聚集主要来自较深层次的分异作用，而不是原地结晶；5)岩浆在上升过程中加入了H2O。

Inclusions of glass in volcanic phenocrysts can reveal the preeruptive state of magma and its pressure of crystallization. Such knowledge is needed to understand volcanic eruptions and the formation and evolution of magmas and ores. This project will determine the vesicularity and crystal content of individual lumps of pumice as well as the compositions of phenocrysts and concentrations of H2O and CO2 in glassy and revitrified inclusions in quartz and feldspar phenocrysts from stratigraphically controlled sites in the rhyolitic Bishop Tuff, Calif. These determinations will be used to assess the following postulates: 1) An accumulation of gas existed in the upper part of the preerupted body of magma; 2) Gas accumulation was mostly responsible for a strong upward decrease in bulk magma density and consequent prevention of convection and survival of magmatic zoning during eruption; 3) the transition from plinian to ash- flow style of eruption corresponds to a sharp change in the amount of accumulated gas; 4) gas accumulation largely derived from deeper levels of differentiation rather than in situ crystallization; 5) H2O was added to magma during ascent.