Zoning of Oxygen Isotope Ratio Within Single Zircons

这项更新建议是为了支持对威斯康星大学麦迪逊分校大量收集的单锆石进行原位离子探针研究，其中包括地球上最古老的锆石，以及来自过铝质岩浆和嵌套火山口复合体的许多锆石。下一次增加的资金的主要科学目标将包括分析地球最古老的锆石（4.4-3.8 Ga）及其矿物内含物;调查大陆地壳随时间的成熟和演变;分析太古代和较年轻的花岗岩类的锆石、石榴石和钛铁矿;岩浆d18 O的生长分带与锆石中其他地球化学的相关性，以确定长英质岩浆房中混染的机制和时间;锆石中氧同位素的分析为锆石的岩石学研究提供了一种有价值的工具。威斯康星州二次离子质谱仪设备将为锆石的这些研究增加一个新的、潜在的革命性的维度。氧同位素比的原位分析将提供晶体内扩散分布、生长分区、遗传和辐射损伤的定量测量。这类资料以前没有。这些研究将对岩浆成因、深熔作用、变质作用以及陆壳的成熟和生长过程提供新的认识。对太古代早期（4.4-3.8 Ga）锆石的研究提供了地球最早期条件的唯一直接证据。该项目将测试最近提出的“早期地球凉爽”的假设，以及太阳系形成和地球吸积2亿年后大陆地壳、液态水和海洋的存在。这些信息对于回答这个问题是必要的：地球何时开始适合生命居住？该项目的更广泛影响包括学术著作的研究和出版、研究生和本科生教育、通过威斯康星州大学地质博物馆进行外展，以及开发研究二氧化碳封存和全球变暖等社会重要问题的新技术。

This renewal proposal is to support in situ ion microprobe studies of single zircons from extensive collections at the University of Wisconsin-Madison, which include the oldest zircons on Earth, plus many zircons from peraluminous magmas and nested caldera complexes. The major scientific goals for this next increment of funding will include the analysis of Earth's oldest zircons, 4.4-3.8 Ga, and their mineral inclusions; investigations of maturation and evolution of continental crust through time; analysis of zircon, garnet and titanites from Archean and younger granitoids; correlation of growth zoning of magmatic d18O with other geochemistry in zircon to determine mechanisms and timing of contamination in felsic magma chambers; and undergoing empirical tests of oxygen diffusion rate in zoned zircon.Analysis of oxygen isotopes in zircon provides a valuable petrologic tool. The Wisconsin Secondary-Ion Mass-Spectrometer facility will add a new, potentially revolutionary, dimension to these studies of zircon. In situ analysis of oxygen isotope ratios will provide quantitative measurement of intra-crystalline diffusion profiles, growth zoning, inheritance, and radiation damage. Such information has not previously been available. These studies will provide new insight into processes of magma genesis, anatexis, metamorphism, and the maturation and growth of continental crust. Studies of early Archean (4.4-3.8 Ga) zircons provide the only direct evidence of the earliest conditions on Earth. This project will test the recent hypotheses of a "Cool Early Earth", and the presence of continental crust, liquid water, and oceans 200 million years after the formation of the Solar System and the accretion of the Earth. This information is necessary to answer the question: When was Earth first habitable for life?Broader impacts of this project include research and publication of scholarly work, graduate and undergraduate education, outreach through the University of Wisconsin Geology Museum, and development of new techniques for studies of problems of societal importance including CO2 sequestration and global warming.