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是复杂的。岩浆的储存条件（P、T、fO 2、fH 2 O）、深部发生的地球化学过程以及岩浆库的寿命都难以确定。确定弧系中岩浆作用时间尺度的一种方法是分析成分环带矿物并应用扩散测时法，但正确解释成分剖面需要了解以下额外信息：（1）岩浆储存条件（例如温度、压力）和（2）用于扩散测时法的单个晶体的寿命。这一信息是特别难以约束弧岩浆，因为它们含有高和可变的水浓度，这会影响结晶温度显着，因为晶体可能是溶解/生长过程的主题，特别是由于许多补充和混合过程。本提案的目标是（1）对P、T、fO 2的作用提供更好的一般约束，fH 2 O对钙碱性体系中主要硅酸盐相稳定性的影响，以及（2）了解多晶部分熔融矿物聚集体的结构演化速率（模拟晶体糊状物中的过程）并评估生长和溶解对扩散曲线（和对估计的时间尺度）的影响。将进行高压实验研究，以限制作为压力（100 - 500 MPa）、fO 2（QFM+1.5 -QFM+3.5）和fH 2 O（熔体中2 - 7重量% H2O）函数的主要相橄榄石、斜方辉石和斜方辉石以及斜长石的结晶温度。起始成分将代表大量原始钙碱性熔体和堪察加半岛的两座火山（Bezymianny和Klyuchevskoy），它们具有不同的管道系统。从Bezymianny（安山英安质）和Klyuchevskoy（玄武岩）的组合物的实验也将被用来约束岩浆储存条件，这是需要准确的扩散测时。这两座火山是检查矿物相记录的时间尺度之间的差异是否可以在可能具有大体积岩浆库的安山-英安岩系统和具有低体积岩浆通道的玄武岩系统之间检测到的理想候选火山（参见研究单元的项目#8）。将用于理解多晶聚集体的结构演化的玄武岩成分将被设计成使它们仅与富Fo橄榄石晶体平衡，并且结果将直接应用于此类过程的模拟（参见研究单元的项目#5）。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熔体温压计，并且对于改进用于预测相关系和下降液线的热力学模型至关重要。