Light Element Investigations of Natural and Experimental Zircon

天然和实验锆石的轻元素研究

• 批准号: 1447404
• 负责人: Dustin Trail
• 金额: $ 29.72万
• 依托单位: University of Rochester
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-02-01 至 2019-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1447404&HistoricalAwards=false
• 关键词: Light; Element; Investigations; Natural; Experimental

The geological events of Earth's past not only shaped the present-day planet, but will also influence the evolution of Earth in the future. In geology, rocks are the key to the past; in many cases they represent the only resource available to study "deep time." However, no known whole rocks exists from before 4 billion years ago. The reservoir of known terrestrial material is limited to very rare "grains of sand" found in only a handful of sediments throughout the world. In the absence of the original rock that hosted these "grains of sand," - or specifically the mineral zircon - there are numerous challenges. This research will address these problems through two complementary approaches. The first involves measurements to deduce the chemical composition of these very rare minerals (zircons), while the second involves the synthesis of the mineral in the controlled environment of a high pressure, high temperature experimental geology laboratory. These experiments - where pressure, temperature, and magma composition can be varied - will serve as a stepping stone to interpret the chemistry of the most ancient known terrestrial samples. The application of these experiments to natural samples will result in new knowledge about the environments and conditions of the earliest Earth (including the composition of magmas), and is therefore a key source of information to understand the evolution of Earth through time. Broader impacts of this work also include the training of undergraduate and graduate students in novel high pressure / high temperature crystal and glass synthesis techniques. Synthetic glasses and crystals make up a component of many consumer products today. Students will also conduct measurements of these materials using modern analytical technology such as a laser ablation inductively coupled plasma mass spectrometer. And finally, secondary school science teachers will benefit from laboratory demonstrations that explain how geologists determine the ages of ancient rocks and minerals; they will also participate in the development of simple diagrams that explain key concepts of geology and geochemistry that they can then use for instruction in their classes. The experimental work for this project will be conducted using a piston cylinder apparatus at the University of Rochester. Zircons will: (i) be synthesized in silicic melts; or (ii) approach equilibrium elemental and isotopic compositions through time series experiments in the presence of fluids. Partition coefficients/isotope compositions of run products will be determined for light stable elements in zircon and co-existing phases. The first goal is to robustly calibrate the incorporation light elements into the zircon lattice as a function of melt composition, melt structure, and temperature. Second, the developed calibrations will be applied to Archean and Hadean zircons. These experiments and the application of the results will play a fundamental role in the quest to link chemical signatures preserved in ancient zircons with early crystal processes. This work will also extend knowledge of the zircon parent rock composition long since gone.

地球过去的地质事件不仅塑造了现在的地球，而且还将影响地球未来的演化。在地质学中，岩石是打开过去的钥匙；在许多情况下，它们是研究“深部时间”的唯一资源。然而，在40亿年前还没有已知的完整岩石存在。已知的陆地物质储藏库仅限于在世界各地的少数沉积物中发现的非常罕见的“沙粒”。在缺乏承载这些“沙粒”的原始岩石，特别是矿物锆石的情况下，存在着无数的挑战。本研究将通过两个相辅相成的方法来解决这些问题。第一个涉及推断这些非常稀有的矿物(锆石)的化学成分的测量，第二个涉及在高压高温实验地质实验室的受控环境中合成矿物。这些实验--其中压力、温度和岩浆成分可以变化--将作为解释最古老的已知陆地样本化学的垫脚石。将这些实验应用于自然样品将产生关于最早地球的环境和条件的新知识(包括岩浆的组成)，因此是了解地球随时间演变的关键信息来源。这项工作的更广泛影响还包括对本科生和研究生进行新型高压/高温晶体和玻璃合成技术的培训。合成玻璃和水晶构成了当今许多消费品的组成部分。学生还将使用现代分析技术，如激光烧蚀电感耦合等离子体质谱仪对这些材料进行测量。最后，中学科学教师将受益于解释地质学家如何确定古代岩石和矿物年龄的实验室演示；他们还将参与开发简单的图表，解释地质和地球化学的关键概念，然后在课堂上使用这些图表进行教学。该项目的实验工作将使用罗切斯特大学的活塞缸装置进行。锆石将：(I)在硅质熔体中合成；或(Ii)在流体存在的情况下，通过时间序列实验接近平衡的元素和同位素组成。将测定锆石及其共存相中轻稳定元素的分配系数/运行产物的同位素组成。第一个目标是作为熔体组成、熔体结构和温度的函数，强有力地校准掺入锆石晶格的轻元素。其次，开发的定标将应用于太古宙和赫甸的锆石。这些实验和结果的应用将在寻求将保存在古代锆石中的化学特征与早期结晶过程联系起来方面发挥基础性作用。这项工作还将扩大对早已不复存在的锆石母岩成分的了解。