Volcanic Processes in Subduction Zone Magmas: Composition, Abundance, and Role of C-O-H-S Volatiles

这个建议包括三个项目，都是为了更全面地了解岩浆混合、结晶、结晶-熔体分离和脱气等岩浆过程是如何在富含气体的俯冲带火山系统中发生的。这些任务包括对在实地研究中收集的样品以及在受控的P、T和fO2条件下实验制备的样品进行一系列分析工作（即电子显微探针、离子探针、傅氏红外光谱）。第一个项目是对1912年卡特迈火山喷发的调查，在那次喷发中，三个成分不同的岩浆在一次事件中喷发出来。该研究既是对岩浆混合过程的研究，也是对Hildreth提出的分带岩浆储藏区假说的检验。第二项任务是获得火山气体组成作为P、T、fO2的函数，以及共存的晶体和熔体组成的基本数据。本研究将考虑CO2-H2O-S组分气相。第三个项目是对几乎同时发生在加州黑丘和邻近的沙斯塔山的火山爆发的研究。本文的目的是确定两次喷发的喷发前岩浆条件，并建立岩浆条件与共存的斜长石和角闪石组成的表达式，这是两次喷发的突出阶段。

RutherfordEAR-0073771This proposal involves three projects, all directed at developing a more complete understanding of how the magmatic processes such as magma mixing, crystallization, crystal-melt separation, and degassing occur in gas-rich, subduction zone volcanic systems. The tasks involve a range of analytical work (i.e., electron microprobe, ion-probe, F.T.I.R spectroscopy) on samples collected during field study, and on samples prepared experimentally under controlled P, T, and fO2, conditions. The first project is an investigation of the 1912 eruption of Mt. Katmai where three compositionally distinct magmas were erupted in a single event. The study is simultaneously an investigation of magma mixing processes, and a test of the zoned magma storage region hypothesis proposed by Hildreth. The second task is one in which fundamental data will be obtained on the composition of volcanic gases as a function of P, T, fO2, and the composition of coexisting crystals and melt. This study will consider CO2-H2O-S composition gas phases. The third project is a study of the volcanic eruptions which occurred almost simultaneously at Black Butte and adjacent Mount Shasta in California. The objective of this work is to determine the pre-eruption magma condition for the two eruptions, and to develop an expression relating magmatic conditions and the compositions of coexisting plagioclase and hornblende which are prominent phases in these eruptions.