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（4Ga）的锆石提供了最早期地球上唯一已知的地球化学记录，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形成于母岩和构造体系中，从完全发育的大陆地壳中的真正花岗岩（严格意义上）的湿熔融到辉长岩地壳中的镁铁质岩中形成。这个问题的解决将有助于限制地球上板块构造、全尺寸硅铝大陆和真正的花岗岩的出现。锆石作为年轻岩石中火成岩、变质和沉积过程的时间胶囊被广泛研究。锆石中锂的组成和同位素比值是研究流体-岩石相互作用与地质时代关系的新工具。我们对锆石中锂的初步研究表明，[Li]在陆壳锆石中的富集程度是洋壳锆石的1000倍以上，而_7Li在陆壳中的分馏程度要大得多。杰克山锆石的成分支持基于氧同位素比值的假设，即早在4.3 Ga地球上就存在海洋和广泛的风化作用。如果是正确的，这表明地球比以前认为的更早地适合生命。提出了锆石中锂成分[Li]和同位素比值（_7Li）以及锆石中矿物包裹体的新研究。锆石将通过离子探针以1 - 10微米的分辨率进行原位分析。主要目标是：1）更好地了解锂的替代和交换锆石的系统学2）系统地识别矿物包裹体中的锆石作为一种工具，以确定寄主岩石的碎屑锆石，和3）约束的成因4.4至4.0 Ga碎屑锆石从杰克山，西澳大利亚州。锆石从选定的年轻岩石，包括镁铁质和长英质洋壳，也将作为可能的类似物，现在失踪的4 Ga母岩进行研究。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、分带和其他放射性同位素系统。其中包括培训研究生和博士后研究员。该方案在培养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学稳定同位素实验室的主要业务赠款，并将帮助开发这里提出的稳定同位素研究所需的Wisc-SIMS IMS-1280离子微探针的新能力。

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.