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。它们存在于基于消费者的聚合物（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；在地球的深处，它们的浓度可以影响岩石在特定温度下是熔融岩浆还是结晶。卤素还影响地壳中稀土元素、钴、铬、铜等关键元素的迁移和运输。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，但关于我们星球最早时期卤素的分布和行为的信息很少。了解这些早期时期是很重要的，因为正是这些信息作为模型的输入，试图了解地球的现在和未来状态。这项研究将有助于了解：(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)之间随时间的运动。由于来自早期地球的宝贵信息很少，研究人员将依靠一个强大的地球化学资源库（锆石矿物，其年龄可追溯到44亿年，可抵抗物理和化学风化），精心设计的实验室实验和质谱分析。这项工作将培养矿物学、最先进的实验地球化学/材料科学和质谱学方面的本科生/研究生。这些培训机会的应用范围超出了地球科学。这些太古宙和冥古宙锆石的卤素测量将与高温高压实验室划分实验相结合，为锆石中的卤素地球化学提供背景。总之，这些信息将用于探索可能在早期地球上盛行的不同的卤素循环模型，其结果将对早期地壳的组成以及可能的早期地球表面水化学产生直接影响。这项研究将首次获得锆石熔体和锆石流体之间详细的F和Cl分配系数。结果还将用于约束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发现的一套~ 39亿年前的锆石，这些锆石在湿花岗岩固体下结晶，可能记录了重要的早太古宙变质或流体流动事件。分配研究将使我们能够广泛地描述早期地球的地壳-水圈系统和地幔之间的卤素交换。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，将进行新的锆石中Cl和F的分析，以更好地表征陆地卤素循环。研究人员将在高P和高T实验、电子显微镜和质谱方面培养一名博士生。第二，“实验地球化学原理”这门课程将作为一门高级混合讲座-实验室课程，设计成一种主动学习的“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，从而完成一篇高级研究论文。最后，PI将设计并制作一个简单的岩石显微镜，使矿物能够在平面偏振光和交叉偏振光下观察。利用这个显微镜的特点，为8-12年级的学生开发一个简单的教育课程。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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 researchers 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 researchers 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.