Zircons Are Forever

EAR-0207340山谷这个项目将调查过去44亿年来地壳的岩浆史。将对矿物锆石进行氧同位素比率、U-Pb年龄和稀土元素浓度的分析。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，在辐射损害程度较低的样品中几乎永远存在。将采用新的离子微探针和激光技术，以实现高精度和精确度，和/或高空间分辨率。将对分区锆石中的单个区域进行分析。将从早太古代、元古界和中生代到新生代对选定的地体进行火成岩矿物研究。太古宙样本将包括来自西澳大利亚杰克山的碎屑锆石，我们在那里发现了过去赠款期间已知的最古老的地球样本。较年轻的样品将记录美国西部爱达荷州和内华达山脉岩层的地壳改造过程。对锆石的分析将与岩浆石榴石、斜纹石、钛铁矿、绿帘石、金红石和石英的新数据进行比较。结合起来，这些结果将提供包括岩浆前捕虏晶、岩浆斑晶和一系列岩浆后蚀变矿物在内的演化成分的记录。这些对锆石及其伴生的火成岩矿物的研究将对了解地壳的起源和演化具有广泛的意义。对太古宙(4.0-4.4Ga)锆石的研究为地球上最早的条件提供了唯一的证据。最近关于“早期地球变冷”的假说将受到检验，这一假说对第一批海洋的形成时间和生命起源具有重要意义。

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.