Experimental Study of Plagioclase Textures and Amphibole Reaction Rims: Implications for Rates of Magmatic Processes

地壳岩浆体中的矿物相以反应结构的形式记录了岩浆混合、加热和脱气的信息，这些反应结构发生在矿物对岩浆状态变化的反应中。通常表现出这些特征的两种矿物是斜长石和角闪石，它们分别表现为筛分、灰状和斑状分带（溶解和生长）和反应边缘（脱气和加热）。这些结构常被用来估计岩浆混合速率和岩浆上升过程。我们建议通过实验限制这些结构在浅层地壳储层条件下形成的速率，使用天然（流纹）英安岩和安山岩起始材料，以及干净的、无分区的、自面体种子晶体。我们提出这项研究的目标是为火山学家在检查地壳岩浆储层的产物时，定量地观察这些反应结构提供必要的校准。前人对这些织构率和成因的研究为我们的研究提供了良好的基础。然而，这项工作存在局限性，需要进一步研究以使约束适用于地壳岩浆储层的广泛矿物熔融成分和P-T条件。我们将在两项任务中实现我们的目标，这两项任务旨在通过实验来限制由加热和成分不平衡引起的斜长石溶解和再生结构的速率，以及由熔体脱气或加热产生的角闪孔反应边缘。第一项任务将重点研究anakchak流纹石和安山岩中斜长石的溶解和边缘生长，使用An20、An37和An80组成的斜长石种子斑晶，在0.1到300 MPa的压力和825到1100摄氏度的温度下，这项任务的目标是限制斜长石溶解速率，作为加热斜长石固体的函数。在另一种成分的斜长石稳定的熔体中，由于化学不平衡而导致斜长石的溶解和再生长。第二项任务将研究Redoubt英安岩和安山岩中寄生和角闪石角闪石角闪洞在这些成分中适合角闪洞稳定性的P-T条件下的破裂。这项任务的目标是将这种反应的已知校准扩展到不同的熔体成分和岩浆条件。此外，为了帮助岩石学家区分减压边缘和加热边缘，还将研究角闪孔的热击穿。这些研究结果将限制浅层地壳储层中重要斜长石和角闪孔反应结构的形成速率。

Larsen and GardnerEAR-0106658Mineral phases in crustal magma bodies record information about magma mixing, heating, and degassing in the form of reaction textures that occur as the mineral responds to the change in state of the magma. Two minerals that commonly show these features are plagioclase and amphibole, exhibiting sieve, dusty, and patchy zoning (dissolution and growth) and reaction rims (degassing and heating) respectively. These textures are often used to estimate the rates of magma mixing and magmatic ascent processes. We propose to experimentally constrain the rates at which these textures form at conditions applicable to shallow-level crustal reservoirs, using natural (rhyo)dacite and andesite starting material, and clean, unzoned, euhedral seed crystals. Our goal for this proposed study is to provide the vital calibrations needed to make observations of these reaction textures quantitatively useful for volcanologists when examining the products of crustal magma reservoirs. Previous work (refs) investigating the rates and causes of these textures have provided a good basis for our proposed study. However, limitations to this work exist, necessitating further study to make constraints useful to a wide range of mineral-melt compositions and P-T conditions applicable to crustal magma reservoirs. We will accomplish our goals in two tasks that are designed to experimentally constrain the rates of dissolution and regrowth textures in plagioclase resulting from heating and compositional disequilibrium, and amphibole reaction rims produced by melt degassing or heating. The first task will focus on plagioclase dissolution and rim growth in Aniakchak rhyodacite and andesite, using plagioclase seed phenocrysts of An20, An37, and An80 composition, at pressures between 0.1 and 300 MPa and temperatures between 825 and 1100 degrees C. The goal of this task is to constrain rates of plagioclase dissolution as a function of heating above the plagioclase solidus, and to examine dissolution and re-growth of plagioclase due to chemical disequilibrium in melts in which plagioclase of another composition is stable. The second task will investigate pargasite and hornblende amphibole breakdown in Redoubt dacite and andesite at P-T conditions appropriate for amphibole stability in these compositions. The goal of this task is to extend known calibrations of this reaction to different melt compositions and magmatic conditions. In addition, the thermal breakdown of amphibole will be investigated in order to help petrologists distinguish between decompression and heating rims. The results of these studies will be constraints on the rates of formation of important plagioclase and amphibole reaction textures in shallow-level crustal reservoirs.