EAR-PF: Quartz-in-zircon: An elastic model for quantifying depth and time scales of crystallization and exhumation of Hadean zircon

Joseph Gonzalez博士获得了美国国家科学基金会EAR博士后奖学金，在帕维亚大学开发锆石中石英包裹体的弹性模型，以更好地了解冥古宙（4ga）的地球条件。锆石在地壳岩石中很常见，是最常用来推断岩石年龄和结晶温度的矿物。尽管人们广泛使用锆石来测定时间和温度，但目前还没有确定锆石结晶深度的方法。该项目的目的是通过研究在4ga古冥古宙锆石的不同生长阶段作为包裹体被捕获的石英晶体，开发一种确定锆石形成深度的方法。冈萨雷斯博士将通过模拟石英包裹体与其锆石宿主之间的弹性相互作用，并将模型结果与现有的锆石年代学和温度测定相结合，来实现这些目标。将锆石中的石英弹性模型应用于来自澳大利亚杰克山省的冥古宙锆石，将有助于了解地球板块构造开始的时间和演化。在担任美国国家科学基金会博士后期间，冈萨雷斯博士将组织并参加由帕维亚大学主办的教育活动，向公众和未来的学生解释正在进行的研究。此外，他将共同指导本科生和研究生，并组织一个关于该项目的专门网站，在那里，任何感兴趣的人都可以访问正在进行的结果的简单语言描述。寄主-包裹体矿物对的弹性模型已成为研究寄主矿物生长过程中包裹体夹带的热气压条件的常用工具。然而，弹性模型只针对弹性各向异性包裹体（如石英）中包含的弹性各向异性寄主矿物（如石榴石）。为了理解弹性各向异性寄主与包裹体矿物（如锆石中的石英包裹体）之间的弹性相互作用，必须考虑寄主与包裹体之间的互易晶体取向（CORs）。在帕维亚大学，将完成一系列的有限元模型来量化晶体取向对锆石宿主与石英包裹体之间应变和应力的影响。一旦知道了取向的影响，模型结果就可以应用于杰克山锆石中的石英包裹体来推断结晶深度。单晶x射线衍射将用于获得锆石主体和石英包裹体的晶体取向和单位胞参数，允许计算包裹体内的残余压力。残余压力和晶体取向可用于有限元模型，并应用于目标包裹体的三维x射线层析模型，以确定石英包裹体在锆石寄主内可能的包裹条件。来自杰克山锆石的石英锆石结果将用于评估现代板块俯冲过程开始于冥古宙相对较冷的热环境的假设。更广泛地说，锆石中石英弹性模型将广泛适用于地壳岩石，并可与其他岩石学方法相结合，以增加对地球过程的理解。该项目更广泛的影响包括指导本科生和研究生以及一般的公众外展活动。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Dr. Joseph Gonzalez has been awarded an NSF EAR postdoctoral fellowship to work at the University of Pavia developing an elastic model for quartz inclusions contained in zircon to better understand Hadean (4 Ga) earth conditions. Zircon is common in crustal rocks and is the most frequently used mineral to infer ages and crystallization temperatures attained by rocks. Despite the extensive use of zircon for time and temperature determinations, there are no methods for determining the depth of zircon crystallization. The objective of this project is to develop a method to determine depth of zircon formation by investigating quartz crystals trapped as inclusions at various stages of growth in 4 Ga old Hadean zircon. Dr. Gonzalez will achieve these goals by modeling the elastic interactions between quartz inclusions and their zircon host and integrating model results with existing zircon geochronologic and thermometric determinations. The quartz-in-zircon elastic model applied to Hadean zircons from the Jack Hills province of Australia will give insights into the timing and evolution of the onset of Earth’s plate tectonics. During his tenure as an NSF Postdoctoral Fellow, Dr. Gonzalez will organize and participate in educational events hosted by the University of Pavia to explain ongoing research to the general public and prospective students. Furthermore, he will co-mentor undergraduate and graduate students and organize a dedicated website about the project, where plain language descriptions of ongoing results will be accessible to anyone interested.Elastic models of host-inclusion mineral pairs have become frequently used tools for investigating the thermobarometric conditions of inclusion entrapment during host mineral growth. However, elastic models have only been developed for elastically anisotropic inclusions (e.g. quartz) contained in elastically isotropic host minerals (e.g. garnet). In order to understand the elastic interactions between elastically anisotropic host and inclusion minerals (e.g. quartz inclusions in zircon), the reciprocal crystallographic orientation (CORs) between the host and inclusion must be incorporated. At the University of Pavia, a series of finite element models will be completed to quantify the effect of crystallographic orientation on the strain and stress between the zircon host and quartz inclusion minerals. Once the effect of orientation is known, model results can be applied to quartz inclusions contained within Jack Hills zircons to infer the crystallization depth. Single crystal X-ray diffraction will be used to obtain the crystallographic orientation and unit cell parameters of the zircon host and quartz inclusion, permitting calculation of the remnant pressure within the inclusion. Remnant pressures and crystallographic orientations can be used in finite element models and applied to 3-D X-ray tomographic models of targeted inclusions to determine the possible entrapment conditions of the quartz inclusion within the zircon host. Quartz-in-zircon results from Jack Hills zircons will be used to evaluate hypotheses that modern style plate subduction processes began under relatively cool thermal regimes in the Hadean Eon. More broadly, the quartz-in-zircon elastic model will be widely applicable to crustal rocks and can be combined with other petrologic methods to increase understanding of Earth processes. Broader impacts of this project include mentoring undergraduates and graduate students and general public outreach activities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.