Volcanic Processes in Volatile-Rich Magmas: Constraints From Phase Equilibria and the Role of the Fluid Phase

富含挥发分岩浆中的火山作用：相平衡和流体相作用的制约。布朗大学地质系P.I.马尔科姆·J·卢瑟福这里提出的研究涉及三个项目，都旨在更全面地了解岩浆混合、结晶、晶体-熔体分离和脱气等过程是如何在富含气的次火山岩浆系统中发生的。这些任务涉及对实地研究期间收集的样品以及在受控条件下通过实验制备的样品进行一系列分析工作。第一个项目是研究压力对角闪石-斜长石-熔体平衡的影响，主要目标是改进含角闪石火山岩的地压计。第二个目标是更好地了解岩浆过程和圣海伦斯山岩浆储存带的作用。这座火山是美国最活跃的火山之一，考虑到该中心喷发的种类和数量，对该中心的研究是一个很好的机会，可以了解火山过程如何在这样的岩浆系统中工作。这一建议中的第二项研究任务涉及实验，以调查火山流体相转移可能起的作用的理论，以解释富硅岩浆系统中氧化和硫浓缩的起源。在这项任务中，将获得有关火山气体的组成随岩浆条件的变化以及共存晶体和熔体的组成的基本数据。这样的数据是火山喷发预测的主要方法之一的基础，也就是监测释放的气体的成分。这项任务的重点是1991年皮纳图博山的这一过程是如何发生的，但类似的玄武岩岩浆注入先前存在的富含硅质的岩浆储存带似乎经常发生，而且经常被认为是镁铁质侵入触发了硅质岩浆的喷发。次火山岩浆储存带中两种岩浆相互作用的过程是可能控制火山喷发行为变化的基本过程之一。最后一项任务在某种程度上是探索性的，建立在最近对苏弗里尔山喷发和更古老、更大的鱼谷凝灰岩喷发的研究中所做的观察基础上。喷发产物中周期性分带的角闪石晶体似乎记录了喷发前岩浆的反复过程。组成带携带了有关它们形成过程的信息，可能还携带了它们生长的时间跨度。提出的研究是通过对这些晶体进行详细的成分和建模研究来提取这些信息的初步尝试。该项目将涉及P.I.和三名研究生，其中两名是女性。

Volcanic processes in volatile-rich magmas: constraints from phase equilibria and the role of the fluid phase. P.I. Malcolm J. Rutherford, Geology Department, Brown UniversityABSTRACT The research proposed here involves three projects, all directed at developing a more complete understanding of how processes such as magma mixing, crystallization, crystal-melt separation, and degassing occur in subvolcanic gas-rich magma systems. The tasks involve a range of analytical work on samples collected during field study, and on samples prepared experimentally under controlled conditions. The first project is an investigation of the pressure effect on hornblende-plagioclase-melt equilibria with a major objective being an improved geobarometer for hornblende-bearing volcanic rocks. A second objective is to better understand magmatic processes and the role of a magma storage zone at Mount St Helens. This volcano is one of the most active in the USA, and study of this center represents a great opportunity to gain an understanding of how volcanic processes work in such magma systems, given the variety and number of eruptions at this center. The second research task in this proposal involves experiments to investigate a theory regarding the possible role of a volcanic fluid phase transfer as an explanation for the origin of oxidation and sulfur enrichment in silica-rich magma systems. This task is one in which fundamental data will be obtained on the composition of volcanic gases as a function of magmatic conditions and the composition of coexisting crystals and melt. Data such as this is fundamental in one of the main methodologies of volcanic eruption prediction, that of monitoring the composition of the gases released. The task is focused on how this process occurred at Mount Pinatubo in 1991, but similar injections of basaltic magma into pre-existing silica-rich magma storage zones appear to happen regularly, and it is often theorized that the mafic intrusion triggers the eruption of the silicic magma. The process of two magma interactions in a subvolcanic magma storage zone is one of fundamental processes that might control the changes in behavior of an erupting volcano. The final task is somewhat exploratory, building on observations that have recently been made in studies of the Soufriere Hills eruption and the much older and larger Fish CanyonTuff eruption. Cyclically zoned hornblende crystals in the eruption products appear to record a recurring process in the pre-eruption magmas. The composition zones carry information about the processes involved in their formation and, potentially about the time span of their growth. The research proposed is a preliminary attempt to extract this information using a detailed compositional and modeling study of these crystals. The project will involve the P.I., and three graduate students, two of whom are women.