Compositional Buffering of Magmas as an Indicator of Magmatic Processes

岩浆的成分缓冲作为岩浆过程的指标

• 批准号: 0003367
• 负责人: Dennis Geist
• 金额: $ 8.39万
• 依托单位: Regents of the University of Idaho
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-06-01 至 2005-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003367&HistoricalAwards=false
• 关键词: Compositional; Buffering; Magmas; Indicator; Magmatic

GeistEAR-0003367Whereas many volcanoes erupt magmas of diverse composition over a wide range of temperatures, others erupt magmas of nearly identical composition over a narrow range of temperature. One or more magmatic processes must buffer the compositions in the latter type of system as the magmas ascend through the lithosphere, and determining and quantifying those processes are the objectives of this proposal. Because the processes involved in buffering cause little variability in whole rock compositions, the main means of the study will be electron and ion microprobe analysis of rehomogenized melt inclusions. Much of this study, and many others, depends on the presumption that melt inclusions reliably reflect the compositional evolution of the magma. To test this presumption, a series of experiments has been designed to assess the degree that inclusions' compositions are reliable. Growing crystals change the compositions of the liquid in a boundary layer whose thickness depends on the diffusivity of the chemical constituents and the growth rate of the crystal. The effect of a compositional boundary layer on the composition of melt inclusions will be simulated by creating artificial melt inclusions by annealing a pre-fractured crystal in the presence of a melt with which it is in equilibrium. Boundary layers of different thicknesses should be generated by a range of cooling rates and different amounts of total cooling.

许多火山在很宽的温度范围内喷出不同成分的岩浆，而另一些火山在很窄的温度范围内喷出几乎相同成分的岩浆。 当岩浆上升通过岩石圈时，一个或多个岩浆过程必须缓冲后一种类型系统中的成分，确定和量化这些过程是本提案的目标。由于在缓冲过程中所涉及的原因在整个岩石成分的变化不大，研究的主要手段将是电子和离子微探针分析的再均匀化熔融包裹体。这项研究和许多其他研究都依赖于熔融包裹体可靠地反映岩浆成分演化的假设。为了验证这一假设，设计了一系列实验来评估包裹体成分的可靠程度。 生长的晶体改变了边界层中液体的成分，边界层的厚度取决于化学成分的扩散率和晶体的生长速率。 将模拟的熔体夹杂物的组合物上的组成边界层的效果，通过创建人工熔体夹杂物退火预断裂晶体的存在下，它是在平衡的熔体。 不同厚度的边界层应通过一定范围的冷却速率和不同的总冷却量来产生。