EAR-PF: Numerical Modeling Perspectives on Zircon Petrochronology

EAR-PF：锆石岩石年代学的数值模拟视角

• 批准号: 1855223
• 负责人: Nathan Andersen
• 金额: $ 17.4万
• 依托单位: Andersen, Nathan Lee
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-04-01 至 2020-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1855223&HistoricalAwards=false
• 关键词: EAR; PF; Numerical; Modeling; Perspectives

Dr. Nathan Andersen has been granted an NSF EAR Postdoctoral Fellowship to work at the University of Oregon to better understand magma evolution by modeling zircon dates in igneous rocks. The accumulation of magma reservoirs in the continental crust is a fundamental process that is responsible for the growth of the crust, the segregation of economically valuable ore deposits, and the generation of volcanic eruptions. Dating and compositional measurements of the mineral zircon are commonly employed to reconstruct the history of magma reservoir growth in the geologic record. Numerical models of magma emplacement and thermo-chemical evolution have promoted an increasingly sophisticated understanding of the processes by which magma is accumulated and stored. However, uniting the zircon and modeling perspectives is subject to the fundamental difficulty of relating chemical analyses made at the crystal-scale of nano and/or micro meters to processes at the magma reservoir scale of meters to tens of kilometers. Thus, these methods are poorly integrated. The objective of this project is to develop a numerical modeling framework that couples the growth rate of zircon crystals to the physical, chemical and thermal evolution of the host magma. This modeling approach will also serve as a basis for videos and animations illustrating magma reservoir processes that will be used to communicate the results of this research to the general public and for the production of publicly available materials for K-12 and undergraduate earth science education. The ubiquity of zircon in the crust and its physical and chemical robustness make it an indispensable tracer of magma reservoir longevity and chemical evolution. Yet, these characteristics also contribute to ambiguous geologic interpretations of the geologic record. While advances in the analysis of zircon over the last two decades have resulted in dramatic improvements in analytical precision and spatial resolution, these new capabilities have revealed previously unappreciated complexities in the zircon record that drive contemporary petrologic controversies. This project will integrate a magma dynamics model --including multi-phase flow, phase equilibrium, and heat flow -- with a model of Zr-diffusion-limited zircon growth that also incorporates a range of trace element partitioning behavior and the development of enriched boundary layers. This framework will address three principal and interrelated questions surrounding the interpretation of zircon data: i) How does the trade-off between the spatial resolution and analytical precision of the zircon date affect its interpretation? Particularly, do dates produced for whole crystals lead to the same conclusions as those produced by in situ techniques? How well do either capture the evolution of the host magma system?; ii) What criteria are most effective at distinguishing inherited zircons from those crystallized in situ?; iii) How do -micrometer to sub-micrometer - scale variations in zircon chemistry relate to the host melt evolution? Initial models will comprise a single magma reservoir in the crust. Guided by the results of these simulations, greater complexity will be implemented through the tracking of individual zircon crystals that move within the magma reservoir, the development of interconnected reservoirs that comprise a trans-crustal magma system, and calibrated simulations designed to reproduce well-studied natural systems. This approach will yield new insights into the timescales and conditions of magma storage, the relationship between voluminous ignimbrites and plutons, and the scaling of volcanic eruptions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

内森·安德森博士已获得美国国家科学基金会的博士后奖学金，在俄勒冈州大学工作，通过模拟火成岩中的锆石年代来更好地了解岩浆演化。大陆地壳中岩浆库的积累是一个基本过程，它导致地壳的生长、有经济价值的矿床的分离以及火山爆发的产生。矿物锆石的定年和成分测量通常用于重建地质记录中岩浆储层生长的历史。岩浆侵位和热化学演化的数值模型促进了对岩浆聚集和储存过程的日益复杂的理解。然而，将锆石和建模观点结合起来面临着将纳米和/或微米晶体尺度的化学分析与几米到几十公里的岩浆库尺度的过程联系起来的根本困难。因此，这些方法的整合性很差。该项目的目标是开发一个数值模拟框架，将锆石晶体的生长速率与寄主岩浆的物理、化学和热演化相耦合。这种建模方法还将作为说明岩浆库过程的视频和动画的基础，这些视频和动画将用于向公众传达本研究的结果，并用于制作K-12和本科地球科学教育的公开材料。 锆石在地壳中的普遍存在及其物理和化学稳定性使其成为岩浆库寿命和化学演化的不可或缺的示踪剂。然而，这些特征也导致地质记录的地质解释模糊不清。虽然在过去的二十年中，锆石分析的进步导致了分析精度和空间分辨率的显著提高，但这些新功能揭示了锆石记录中以前未被认识到的复杂性，这些复杂性推动了当代岩石学的争议。该项目将整合一个岩浆动力学模型-包括多相流，相平衡和热流-与锆扩散限制锆石生长的模型，还包括一系列的微量元素分配行为和富集边界层的发展。该框架将解决围绕锆石数据解释的三个主要和相互关联的问题：i）锆石数据的空间分辨率和分析精度之间的权衡如何影响其解释？特别是，整个晶体产生的日期是否会导致与原位技术产生的结果相同的结论？两者对宿主岩浆系统的演化捕捉得如何？; ii）什么标准是区分继承锆石和原地结晶锆石最有效的标准？（三）微米到亚微米尺度的锆石化学变化与主熔体演化有何关系？最初的模型将包括地壳中的单一岩浆库。在这些模拟结果的指导下，将通过跟踪在岩浆储层内移动的单个锆石晶体，开发包括跨地壳岩浆系统的相互连接的储层，以及旨在重现经过充分研究的自然系统的校准模拟来实现更大的复杂性。这一方法将对岩浆储存的时间尺度和条件、大量熔结凝灰岩和岩体之间的关系以及火山爆发的规模产生新的见解。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。