Lithium Isotopes and Mineral Inclusions in Zircons- 4.4 Ga to Recent

智力上的优点。年龄超过 40 亿年 (4 Ga) 的锆石提供了唯一已知的最早地球条件的地球化学记录，他们的研究引起了相当大的兴趣和争议。它们被不同地解释为在母岩和构造体系中形成，从完全发育的大陆地壳中真正的花岗岩（sensu stricto）的湿熔融到辉长岩地壳中的基性岩中的形成。这个问题的解决将有助于限制地球上板块构造、全尺寸唾液质大陆和真正的花岗岩的出现。锆石作为较年轻岩石中火成岩、变质和沉积过程的时间胶囊而被广泛研究。锆石中的锂成分和同位素比率可能是耦合流体-岩石相互作用与地质时间的强大新工具。我们对锆石的初步锂研究表明，与来自洋壳的锆石相比，来自大陆地壳的锆石中的 [Li] 富集了 1000 多倍，并且 _7Li 的值在大陆地壳中更加分馏。杰克山锆石的成分支持基于氧同位素比的假设，即地球上早在 4.3 Ga 就存在海洋和广泛的风化作用。如果正确，这表明地球适合生命生存的时间比之前认为的要早得多。我们提出了关于锆石中锂成分 [Li] 和同位素比 (_7Li) 以及锆石中矿物包裹体的新研究。锆石将通过离子微探针以 1 - 10 微米的分辨率进行原位分析。主要目标是：1) 更好地了解锆石中锂取代和交换的系统学；2) 系统地识别锆石中的矿物包裹体，作为确定碎屑锆石母岩的工具；3) 限制西澳大利亚杰克山 4.4 至 4.0 Ga 碎屑锆石的成因。来自选定的较年轻地体（包括镁铁质和长英质洋壳）的锆石也将作为现在失踪的 4 Ga 母岩的可能类似物进行研究。这些研究和数据将与锆石和主岩的其他地球化学参数相关联，包括：年龄、氧同位素比、微量元素、分区和其他放射性同位素系统。更广泛的影响。其中包括研究生和博士后研究员的培训。该项目在培训学术研究人员方面非常成功； 20名毕业生担任研究或教学职务，10名毕业生建立了自己的稳定同位素实验室。这笔赠款将是华盛顿大学地质稳定同位素实验室的主要运营赠款，并将帮助开发 Wisc-SIMS ims-1280 离子微探针的新功能，这是本文提出的稳定同位素研究所需的。

Intellectual merit. Zircons that are older than 4 billion years ( 4 Ga) provide the only known geochemical record of conditions on earliest Earth, and their study has stimulated considerable interest and controversy. They are variously interpreted to have formed in parent rocks and tectonic regimes ranging from wet melting of true granites (sensu stricto) in fully developed continental crust to forming in mafic rocks in gabbroic crust. Resolution of this question would help constrain the emergence on Earth of plate tectonics, full-size sialic continents, and true granites. Zircons are widely studied as time capsules of igneous, metamorphic, and sedimentary processes in younger rocks. Lithium compositions and isotope ratios in zircon are potentially a powerful new tool for coupling fluid-rock interaction to geologic time. Our preliminary lithium studies in zircons show that [Li] is enriched by a factor of over 1000 in zircons from continental crust vs. zircons from ocean crust and that values of _7Li are much more fractionated in continental crust. The compositions of Jack Hills zircons support the hypothesis, based on oxygen isotope ratios, that oceans and extensive weathering existed on Earth as early as 4.3 Ga. If correct, this indicates that Earth was hospitable for life much earlier than previously thought. We propose new studies of lithium composition [Li] and isotope ratio (_7Li) in zircons and of mineral inclusions in zircons. Zircons will be analyzed in situ by ion microprobe at 1 - 10 micron resolution. The primary goals will be to:1) better understand the systematics of Li substitution and exchange in zircon2) systematically identify mineral inclusions in zircons as a tool to determine host rock for detrital zircons, and3) constrain the genesis of 4.4 to 4.0 Ga detrital zircons from the Jack Hills, Western Australia. Zircons from selected younger terranes, including mafic and felsic ocean crust, will also be studied as possible analogs for the now missing 4 Ga parent rocks. These studies and data will be correlated to other geochemical parameters of zircons and host-rocks including: age, oxygen isotope ratio, trace elements, zoning, and other radiogenic isotope systems.Broader impacts. These include training of graduate students and postdoctoral fellows. This program has been very successful in training academic researchers; 20 graduates have research or teaching positions and 10 have established their own stable isotope laboratories. This grant will be the main operating grant of the UW Geology Stable Isotope Laboratory and will help develop the new capabilities of the Wisc-SIMS ims-1280 ion microprobe that are required by the stable isotope research proposed here.