Collaborative Research: Tracing ca. 4 billion years of volatile cycling in magmas and fluids: insights from halogens in synthetic and natural zircons

卤素（例如，氯和氟）是日常生活中遇到的关键成分。它们存在于消费型聚合物（塑料）、饮用水、牙膏、游泳池、清洁用品和食盐中。 在地球科学中，它们是海水的关键成分之一;在我们的星球深处，它们的浓度可以影响岩石在给定温度下是熔融岩浆还是结晶。卤素还影响地壳中关键元素的流动性和运输，如稀土元素，钴，铬和铜等，虽然研究人员对固体地球与海洋/大气之间的卤素相互作用有一些基本的了解，但有关卤素在地球最早期的分布和行为的信息很少。这些早期的时间是很重要的，因为它是作为输入到模型，试图了解地球的现在和未来的状态的信息。 这项研究将有助于理解（1）地球岩石内部的卤素和（2）海洋/大气之间的复杂联系，以及（1）和（2）之间的运动。 由于来自最早期地球的宝贵信息很少，研究小组将依靠强大的地球化学储存库（矿物锆石，其抵抗物理和化学风化，年龄可追溯到44亿年），精心设计的实验室实验和质谱法。 这项工作将教育本科生/研究生在矿物学，国家的最先进的实验地球化学/材料科学和质谱。 这些培训机会的应用范围超出了地球科学。这些太古代和冥古宙锆石的卤素测量将结合高温和高压实验室分区实验，提供锆石中的卤素地球化学背景。 这些信息将用于探索早期地球上可能存在的不同卤素循环模型，其结果将对早期地壳的组成和可能的早期地球表面水化学产生直接影响。 这项研究将产生有史以来第一个详细的F和Cl分配系数之间的锆石熔体和锆石流体。 结果也将被用来限制早期地球火成岩系统（锆石熔体）的F和Cl含量。此外，锆石-流体分配系数将应用于先前确定的一套约39亿年的锆石，其结晶低于湿花岗岩固相线，并可能记录重要的太古代早期变质或流体流动事件。 分区研究将能够对早期地球的地壳-水圈系统和地幔之间的卤素交换进行广泛的定性。 将进行锆石中Cl和F的扩散研究，以更好地确定锆石保留原生Cl和F的条件。最后，新的Cl-和F-的锆石分析将进行，以更好地表征陆地卤素循环。 PI将在高P和T实验，电子显微镜和质谱法方面培训一名博士生。 其次，“实验地球化学原理”课程将作为高年级混合讲座-实验室课程提供，设计为主动学习“工作室”形式。第三，本科生将进行与本提案目标直接相关的实验室研究，从而完成高级研究论文。 最后，PI将设计和建造一个简单的岩相显微镜，使矿物观察在平面偏振光和交叉偏振光，开发一个简单的教育课程，使用这种显微镜的功能，为8- 12年级的学生。这个奖项反映了NSF的法定使命，并已被认为是值得支持的评估使用基金会的智力价值和更广泛的影响审查标准。

Halogens (e.g., chlorine and fluorine) are key ingredients encountered in everyday life. They are found in consumer-based polymers (plastics), drinking water, toothpaste, swimming pools, cleaning supplies, and table salt. In the geosciences they represent one of the key components in ocean water; deeper into our planet, their concentration can affect whether a rock is a molten magma or crystalline at a given temperature. Halogens also affect the mobility and transport of critical elements in the crust like rare earth elements, cobalt, chromium, and copper etc. While researchers have some basic understanding of halogen interactions between the solid earth and the ocean/atmosphere, there is scant information about distribution and behavior of halogens during the very earliest times of our planet. These early times are important to understand because it is this information that serves as inputs into models that seek to understand the present and future state of Earth. This research will help to understand the complex connections between: (1) halogens inside of Earth’s rocks and (2) the ocean/atmosphere, and the movement between (1) and (2) through time. Since there is precious little information from the earliest Earth, the research team will rely upon a robust geochemical repository (the mineral zircon which resists physical and chemical weathering with ages that extend back to 4.4 billion years), carefully designed laboratory experiments, and mass spectrometry. This work will educate undergraduate/graduate students in mineralogy, state-of-the art experimental geochemistry/materials science, and mass spectrometry. These training opportunities have applications that extend beyond the geosciences. Halogen measurements of these Archean and Hadean zircons will be combined with high-temperature and high-pressure laboratory partitioning experiments to provide context for halogen-in-zircon geochemistry. Together, this information will be used to explore different halogen cycling models that may have prevailed on the early Earth, the outcome of which would have direct consequences for the composition of the early crust and possibly early Earth surface water chemistry. This research will yield the first ever detailed F and Cl partition coefficients between zircon-melt and zircon-fluid. Results will also be used to constrain the F and Cl contents of early Earth igneous systems (zircon-melt). In addition, zircon-fluid partition coefficients will be applied to a previously identified suite of ~3.9 billion- year-old zircons, which crystallized below the wet granite solidus and may record significant early Archean metamorphic or fluid-flow events. The partitioning studies will enable a broad characterization of halogen exchange between the crust-hydrosphere system and the mantle of the early Earth. Diffusion studies for Cl and F in zircon will be carried out to better establish the conditions under which zircon will retain primary Cl and F. Finally, new Cl- and F-in-zircon analyses will be undertaken, to better characterize terrestrial halogen cycling. The PI will train a PhD student in high P and T experimentation, electron microscopy, and mass spectrometry. Second, the course “Principles of Experimental Geochemistry”, will be offered as an upper division hybrid lecture- laboratory-based course designed as an active learning ‘studio’ format. Third, an undergraduate student will conduct laboratory research directly related to the objectives of this proposal, leading to a senior research thesis. And finally, the PI will design and build a simple petrographic microscope to enable mineral viewing in plane polarized and cross polarized light to develop a simple educational lesson, using the features of this microscope, for 8-12th grade students.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.