Insights into the Earliest Magmas from Inclusions and Trace Elements in Zircon

从锆石中的包裹体和微量元素洞察最早的岩浆

• 批准号: 1551437
• 负责人: Timothy Harrison
• 金额: $ 28.06万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-02-15 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1551437&HistoricalAwards=false
• 关键词: Insights; into; Earliest; Magmas; Inclusions

Earth's first few hundred million years remains one of the last frontiers for fundamental discovery in the earth sciences but lacks a rock record. Grains of the mineral zircon deposited in younger sediments are the best known resource for investigating this period. Zircons from the Jack Hills locality in Western Australia have yielded great insights into the character of Hadean (i.e., 4 billion years ago, or Ga) magmas through investigation of both their trace chemistry and exotic phases trapped within the zircons as they grew (i.e., mineral inclusions). However, fully exploiting the information recorded in these zircons and their inclusions has been hampered by a lack of foundational studies. This project constitutes a series of investigations into various aspects of zircon trace element chemistry and inclusion character, which will allow for better understanding of the geologic processes acting on Hadean Earth. Fundamental observations on the trace element chemistry and mineral inclusion character of the Hadean Jack Hills zircons have revealed several aspects of the chemistry and mineralogy of the magmas from which they grew. Quartz and muscovite dominate thelikely primary inclusion assemblages of the zircons, suggesting shale-like precursors. The zircons also contain rare oxide, sulfide, and carbonaceous phases relevant to various under-explored aspects of their host magma chemistry, especially volatiles. However, questions remain as to how to distinguish primary inclusion assemblages, their relationship to magma chemistry, and the relevance of various aspects of host zircon trace chemistry to magmatic volatile contents.This project constitutes several allied investigations of Hadean zircon trace chemistry and inclusion character which can reveal important aspects of source melt chemistry and define objective criteria for distinguishing primary versus altered mineral inclusions. The discovery of carbonaceous inclusions in Hadean zircons allows for the documentation of carbon isotopic variations during the Hadean and early Archean. In addition, the relationship of source magma trace element content and redox conditions with zircon chemistry and inclusion assemblages will be investigated using a suite of ~400 million year old granitoids of known composition and origin, and the results applied to better understand the last dark age of Earth history.

地球最初的几亿年仍然是地球科学基础发现的最后前沿之一，但缺乏岩石记录。 在较年轻的沉积物中沉积的锆石矿物颗粒是研究这一时期的最佳已知资源。 来自西澳大利亚州杰克山的锆石对冥古宙的特征有很好的了解（即，40亿年前，或Ga）岩浆，通过研究它们的微量化学和在锆石生长时被捕获的外来相（即，矿物夹杂物）。 然而，由于缺乏基础研究，充分利用这些锆石及其包裹体中记录的信息受到了阻碍。 该项目对锆石微量元素化学和包裹体特征的各个方面进行了一系列调查，这将有助于更好地了解作用于冥古宙地球的地质过程。对冥古宙杰克山锆石的微量元素化学和矿物包裹体特征的基本观察揭示了它们生长的岩浆的化学和矿物学的几个方面。 石英和白云母占主导地位thelikely原生包体组合的锆石，建议页岩样的前体。锆石还含有稀有的氧化物，硫化物和碳相有关的各种未开发的方面，其主机岩浆化学，特别是挥发分。然而，问题仍然存在，如如何区分原生包裹体组合，它们与岩浆化学的关系，和相关的主机锆石微量化学的各个方面，岩浆volatile contents.This项目构成了几个联盟的调查深源锆石微量化学和包裹体的字符，可以揭示源熔体化学的重要方面，并确定区分原生与蚀变矿物包裹体的客观标准。在冥古宙锆石中发现碳质包裹体，为研究冥古宙和太古代早期的碳同位素变化提供了依据。 此外，源岩浆微量元素含量和氧化还原条件与锆石化学和包裹体组合的关系将使用一套~ 4亿年的已知成分和起源的花岗岩类进行研究，其结果将用于更好地了解地球历史的最后一个黑暗时代。