Phase stability fields in calc-alkaline magmatic systems and textural evolution of crystalline aggregates

钙碱性岩浆系统中的相稳定场和晶粒的结构演化

• 批准号: 439826178
• 负责人: Professor Dr. Sumit Chakraborty, Ph.D.
• 金额: --
• 依托单位: Institut für Geologie, Mineralogie und Geophysik
• 依托单位国家: 德国
• 项目类别: Research Units
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/439826178?language=en
• 关键词: Phase; stability; fields; calc; alkaline

Magma plumbing systems of calc-alkaline volcanoes are complex. The magma storage conditions (P, T, fO2, fH2O), the geochemical processes occurring at depth as well as the lifetime of magma reservoirs are difficult to constrain. One approach to determine time scales of magmatic processes in arc systems is to analyze compositionally zoned minerals and to apply diffusion chronometry, but the correct interpretation of the compositional profiles requires additional information to be known: (1) the magma storage conditions (e.g. temperature, pressure) and (2) the lifetime of the individual crystals used for diffusion chronometry. This information is particularly difficult to constrain for arc magmas because they contain high and variable water concentrations, which affect crystallization temperatures significantly, and because crystals may be the subject of dissolution/growth processes, especially due to numerous replenishment and mixing processes. The goals of this proposal are (1) to provide better general constraints on the role of P, T, fO2, fH2O on the stability of main silicate phases in calc-alkaline systems and (2) to understand the rate of textural evolution of polycrystalline partially molten mineral aggregates (simulating processes in a crystal mush) and to evaluate the influence of growth and dissolution on diffusion profiles (and on estimated time scales). High pressure experimental studies will be conducted to constrain the crystallization temperatures of the main phases olivine, clino- and orthopyroxene, and plagioclase as a function of pressure (100 - 500 MPa), fO2 (QFM+1.5 -QFM+3.5) and fH2O (2 to 7 wt% H2O in melt). The starting compositions will be representative of the large variety of primitive calc-alkaline melts and of two volcanoes from Kamchatka (Bezymianny and Klyuchevskoy), which have different plumbing systems. The experiments with compositions from Bezymianny (andesitic-dacitic) and Klyuchevskoy (basaltic) will also be used to constrain the magma storage conditions, which are needed for accurate diffusion chronometry. These two volcanoes are ideal candidates to check if differences between time scales recorded in mineral phases can be detected between andesitic-dacitic systems with probably large volume magma reservoirs and basaltic systems with low-volume magma channel (see Project #8 of the research unit). The basaltic compositions that will be used to understand the textural evolution of polycrystalline aggregates will be designed so that they are in equilibrium with Fo-rich olivine crystals only and the results will be directly applied to simulation of such processes (see Project #5 of the research unit). The experimental results will also allow us to test and recalibrate mineral-melt thermobarometers available so far and are crucial to improve thermodynamic models that are designed to predict phase relations and liquid lines of descent.

钙碱性火山的岩浆管道系统很复杂。岩浆存储条件（P，T，FO2，FH2O），在深度以及岩浆储层的寿命上发生的地球化学过程很难约束。确定ARC系统中岩浆过程时间尺度的一种方法是分析构图分区矿物质并应用扩散时间表，但是对组成曲线的正确解释需要已知的其他信息：（1）岩浆存储条件（例如，温度，例如，温度，压力）和（2）用于扩散时间表的单个晶体的寿命。由于弧岩浆包含较高和可变的水浓度，因此这些信息尤其难以限制，这会显着影响结晶温度，并且由于晶体可能是溶解/生长过程的主题，尤其是由于大量补充和混合过程。该提案的目标是（1）对P，T，FO2，FH2O在Calcalaline Systems中主要硅酸盐阶段的稳定性以及（2）了解Polycrystalline的质地演化速率以及（2），提供更好的一般限制。部分熔融的矿物聚集体（在晶体糊中模拟过程），并评估生长和溶解对扩散谱的影响（以及估计的时间尺度）。将进行高压实验研究，以限制主要相的结晶温度橄榄石，临床和正py耐氧烯，以及斜长石，与压力（100-500 MPa），FO2（QFM+1.5 -QFM+3.5）和FH2O（FH2O（FH2O）的函数熔体中的2至7 wt％H2O）。起始组合物将代表具有不同管道系统的各种原始骨碱性融化和来自Kamchatka（Bezymianny和Klyuchevskoy）的两座火山。来自Bezymianny（Andesitic-Dacitic）和Klyuchevskoy（玄武岩）组成的实验也将用于限制岩浆存储条件，这是准确的扩散时间表所需的。这两个火山是理想的候选者，可以检查是否可以在具有较大体积的岩浆储层和具有低体积的岩浆通道的矿物阶段中记录的时间尺度之间的差异（参见研究单元的项目＃8） 。将设计用于理解多晶骨料的质地演化的玄武岩成分将被设计，以便它们仅与富含FO的橄榄石晶体保持平衡，并将结果直接应用于模拟此类过程（请参见项目＃5研究单位）。实验结果还将使我们能够测试和重新校准迄今为止可用的矿物融化热力计，并且对于改善旨在预测相关相关和液态下降的热力学模型至关重要。