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

Joseph Gonzalez博士已获得NSF博士后研究金，在帕维亚大学工作，开发锆石中石英夹杂物的弹性模型，以更好地了解Hadean（4 Ga）地球条件。 锆石在地壳岩石中很常见，是最常用于推断岩石年龄和结晶温度的矿物。尽管锆石被广泛用于时间和温度的测定，但还没有确定锆石结晶深度的方法。本项目的目的是开发一种方法，通过调查在4Ga古老的冥古宙锆石中作为包裹体在不同生长阶段捕获的石英晶体来确定锆石形成的深度。Gonzalez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地质年代学和温度测定相结合来实现这些目标。石英在锆石弹性模型应用于从杰克山省的澳大利亚Hadean锆石将提供洞察地球的板块构造的开始的时间和演变。在担任NSF博士后研究员期间，冈萨雷斯博士将组织和参加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，并组织一个专门的网站有关该项目，在那里正在进行的结果将访问任何人感兴趣的平实语言描述。弹性模型的主机包体矿物对已成为常用的工具，用于调查包体包埋在主机矿物生长过程中的温压条件。然而，弹性模型只开发了弹性各向异性夹杂物（如石英）中包含的弹性各向同性的主机矿物（如石榴石）。为了理解弹性各向异性的主体矿物和包裹体矿物（例如锆石中的石英包裹体）之间的弹性相互作用，主体和包裹体之间的相互晶体学取向（CORs）必须被纳入。在帕维亚大学，将完成一系列有限元模型，以量化晶体取向对锆石宿主和石英包裹体矿物之间的应变和应力的影响。一旦定向的影响是已知的，模型的结果可以应用到包含在杰克山锆石的石英夹杂物，以推断结晶深度。单晶X射线衍射将用于获得锆石主体和石英夹杂物的晶体学取向和晶胞参数，从而计算夹杂物内的残余压力。残余压力和晶体学取向可用于有限元模型中，并应用于目标包裹体的3-D X射线断层扫描模型，以确定锆石宿主内石英包裹体的可能捕获条件。来自杰克山锆石的石英锆石结果将被用来评估现代风格的板块俯冲过程开始于冥古宙相对较冷的热制度下的假设。更广泛地说，锆石中的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。该项目的更广泛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NSF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.