Acessory Minerals and Crustal Processes

智力上的优点。这项以成就为基础的更新(ABR)提案要求提供资金，以继续进行与大陆地壳中辅助矿物的性质有关的多方面研究计划。总的目标是加强确定地壳地质事件和过程的时间和强度的能力，范围从火成岩活动和变质作用到抬升和折返速率。上一个供资周期(2005-2009年)的研究主要集中在开发工具和技术来描述高温过程：即锆石、金红石、钛铁矿和石英的地质温度计以及评估其抗扩散重置能力所需的扩散数据。探索性地研究了缺陷在氧扩散中的作用，并开发了表征副矿物中氦扩散的技术。由于U和Th放射性衰变产生的He的扩散在定量地壳浅层岩石的时间-温度历史方面有许多应用，因此未来的研究将在很大程度上转向这一领域的应用。(U-Th)/He热年代学是描述地质系统热历史的一种强有力的技术。这项技术的基础是对氦在副矿物(如磷灰石、锆石、钛铁矿、氙矿和独居石)中的迁移性(扩散)的了解。氦在锆石和磷灰石中扩散的测量结果与从含放射性成因氦的天然晶体的整体释放研究中得出的信息大体一致。在锆石的情况下，直接仿形显示了显著的扩散各向异性，扩散速度更快，与分子动力学模拟通常预测的择优晶向平行。未来的努力将集中在：1)找出磷灰石批量释放和直接剖析结果之间差异的根本原因；2)将研究扩展到其他辅助矿物；3)评估可能的氦饱和对扩散的影响；4)评估辐射损伤在氦扩散中的作用；以及5)开发用于模拟非球形颗粒中各向异性扩散的计算机代码。还将继续开发辅助矿物温度计，包括评估压力对锆石钛温度计的影响，并校准磷灰石结晶温度计。拟议的研究将提供有关地壳中关键稀有元素矿物行为的基本信息，并能够从中提取有关地壳过程和演化的信息。重点是基本实验数据的获取，但系统具有战略性目标，希望在对固体地球科学具有广泛意义的领域进一步加深知识。这项工作为解决岩石学和构造问题提供了新的工具，并有望导致分子动力学的完善和矿物中扩散过程的第一性原理模拟。该项目将有助于开发量化变质岩和火成岩的T-T历史的方法。由于这项工作的重点是含有放射性元素的矿物，因此结果也将与放射性废物隔离领域(例如，扩散测量)直接相关。此外，拟议的研究还包括开发新的实验方法和晶体生长技术，这些技术可能会在其他领域(如陶瓷工程)中得到应用。最后，该项目将支持一名博士生和几名本科生参与拟议的研究。

Intellectual merit. This accomplishment-based renewal (ABR) proposal requests funding to continue a multi-faceted program of research bearing on the properties of accessory minerals in the Earth's continental crust. The overall goal is to enhance capabilities for determining the timing and intensity of crustal geologic events and processes ranging from igneous activity and metamorphism to uplift and exhumation rates. Research during the last funding cycle (2005-2009) focused mainly on development of tools and techniques for characterizing high-temperature processes: i.e., geothermometers for zircon, rutile, titanite and quartz and the diffusion data needed to evaluate their resistance to diffusive resetting. Exploratory efforts were made to investigate the role of defects on oxygen diffusion, and to develop techniques to characterize He diffusion in accessory minerals. Because diffusion of He produced by radioactive decay of U and Th has numerous applications in quantifying time-temperature histories of shallow crustal rocks, future research will shift substantially toward applications in this area. (U-Th)/He thermochronometry is a powerful technique for characterization of thermal histories of geologic systems. Underpinning the technique is knowledge of the mobility (diffusion) of He in accessory minerals (e.g., apatite, zircon, titanite, xenotime and monazite). Measurements of He diffusion in zircon and apatite are generally consistent with information deduced from bulk-release studies of natural crystals containing radiogenic He. In the case of zircon, direct profiling reveals substantial diffusive anisotropy, with faster diffusion rates parallel preferred crystallographic orientations as generally pedicted by molecular dynamics simulations. Future efforts will focus on: 1) identifying the underlying cause for differences between bulk-release and direct-profiling results for apatite; 2) extending the study to other accessory minerals; 3) assessing possible He saturation effects on diffusion; 4) evaluating the role of radiation damage in He diffusion; and 5) development of computer codes for modeling anisotropic diffusion in non-spherical grains. Work will also continue on development of accessory-mineral thermometers, including evaluation of the effect of pressure on the Ti-in-zircon thermometer and calibration of a crystallization thermometer for apatite.The proposed research will provide fundamental information on the behavior of key rare-element minerals in the Earth's crust and enable extraction of information from them regarding crustal processes and evolution. Emphasis is on acquisition of basic experimental data, but systems are strategically targeted in the hope of furthering knowledge in areas of broad significance to the solid-earth sciences. This work provides new tools for addressing petrological and tectonic problems, and will hopefully lead to refinement of molecular dynamics and first-principles modeling of diffusion processes in minerals.Broader impacts. This project will contribute to development of methods to quantify T-t histories of metamorphic and igneous rocks. Because the work focuses upon minerals that contain radioactive elements, results will also be directly relevant the radioactive waste isolation arena (e.g., He diffusion measurements). Moreover, the proposed studies involve development of new experimental methods and crystal-growth techniques that may find applications in other fields (e.g., ceramic engineering). Lastly, this project will support one PhD student and involvement of several undergraduates in aspects of the proposed research.