Zircons Are Forever

这个项目将调查过去44亿年里地壳的岩浆历史。对锆石进行氧同位素比值、U-Pb年龄和稀土元素浓度分析。锆石的高熔化温度、化学惰性和硬度创造了一个地球化学信息的时间胶囊，它几乎永远存在于辐射损伤较低的样品中。新的离子探针和激光技术将用于高精度和高精度，和/或高空间分辨率。对分带锆石内的单域进行分析。选取早太古宙、元古代、中生代至新生代的岩浆岩进行研究。太古宙样本将包括来自西澳大利亚杰克山的碎屑锆石，我们在过去的资助时期在那里发现了地球上已知最古老的样本。较年轻的样本将记录美国西部爱达荷州和内华达山脉岩基的地壳改造过程。对锆石的分析将与岩浆石榴石、坏辉石、钛矿、绿柱石、金红石和石英的新数据进行比较。这些结果将提供包括岩浆前异晶、岩浆斑晶和一系列岩浆后蚀变矿物在内的演化成分记录。这些锆石及其伴生火成岩矿物的研究将对认识地壳的起源和演化具有广泛的意义。对太古宙（4.0 - 4.4 Ga）锆石的研究提供了地球上最早条件的唯一证据。最近提出的“凉爽的早期地球”假说将得到验证，这将对第一个海洋的时间和生命的起源产生影响。

EAR-0207340ValleyThis project will investigate the magmatic history of the Earth's crust over the past 4.4 billion years. The mineral zircon will be analyzed for oxygen isotope ratio, U-Pb age, and rare earth element concentration. The high melting temperature, chemical inertness, and hardness of zircon creates a time capsule of geochemical information that lasts virtually forever in samples with low amounts of radiation damage. New ion microprobe and laser techniques for high precision and accuracy, and/or high spatial resolution will be employed. Single domains within zoned zircons will be analyzed. Igneous minerals will be studied from selected terranes of early Archean, Proterozoic and Mesozoic through Cenozoic age. Archean samples will include detrital zircons from the Jack Hills, Western Australia, where we discovered the oldest known sample of the Earth in the past grant period. The younger samples will document processes of crustal reworking in the Idaho and Sierra Nevada batholiths of the western U.S. Analyses of zircon will be compared to new data for magmatic garnet, baddeleyite, titanite, epidote, rutile and quartz. In combination, these results will provide a record of evolving compositions including pre-magmatic xenocrysts, magmatic phenocrysts and a range of post magmatic alteration minerals. These studies of zircons and associated igneous minerals will have broad significance for understanding the origin and evolution of the Earth's crust. Studies of the Archean (4.0 to 4.4 Ga) zircons provide the only evidence of the earliest conditions on Earth. The recent hypothesis of a "Cool early Earth" will be tested, which has implications for the timing of the first oceans and the origin of life.