The Effects of Radiation Damage and Crystallography on Helium Diffusion in Minerals: An Integrated Bulk and Laser Ablation Depth Profiling Study

辐射损伤和晶体学对矿物中氦扩散的影响：综合体和激光烧蚀深度剖析研究

• 批准号: 1346321
• 负责人: Kip Hodges
• 金额: $ 27.39万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-05-15 至 2019-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1346321&HistoricalAwards=false
• 关键词: Effects; Radiation; Damage; Crystallography; Helium

Thermochronology - the study of temperature histories for geologic samples using the tools of isotope and nuclear geochemistry - has evolved into a fundamental part of earth system research. Just as the geochemistry community in the 1970's and 1980's led an explosion in the development of new isotopic tracers as probes of mantle and crustal evolution, the thermochronology community is now driving a rapid expansion in the temperature range and precision of temperature history reconstructions. Such reconstructions have a variety of applications to understanding aspects of earth system evolution relevant to society. Reconstructing the thermal history of sedimentary basins is essential for our determination of oil and gas potential. More generally, we know that thermal histories are of rocks in the upper crust are strongly influenced by erosional processes. Those processes are, in turn, influenced by climatic variations such that low-temperature thermochronometry - the focus of this research project - has become our primary means of reconstructing past climate fluctuations on timescales of millions of years. Such information is essential for us to establish long-term climate variations that can help us to better compare current climate trends to those further back in earth history, and to more fully evaluate the societal implications of extreme changes in climate. The practical utility of mineral-isotopic systems for thermochronometry, is limited by the quality of our knowledge of helium diffusion kinetics. Recent experimental studies of apatite and zircon suggest that radiation damage substantially affects the diffusivity of helium. Recent studies of zircon suggest a strong helium diffusion anisotropy (orders of magnitude greater parallel to the c crystallographic direction). The investigators propose a study aimed at systematically quantifying both of these influences on helium diffusion on a variety of minerals with proven or anticipated value for (U-Th)/He thermochronometry: monazite, rutile, titanite, xenotime, and zircon. They will prepare samples with various levels of radiation damage through thermal annealing and proton irradiation for two kinds of diffusion experiments: 1) the more familiar incremental heating, bulk diffusion approach through which most of the currently available helium diffusion data were obtained; and 2) a newly developed laser ablation depth profiling approach that enables the interrogation of laboratory induced diffusion profiles in predetermined crystallographic orientations. The ultimate goal of the project will be to contribute to the development of a schema for assigning appropriately unique diffusion parameters to individual crystals so that themochronologists can more confidently use measured dates for thermal history reconstructions.

热团学 - 使用同位素和核地球化学工具对地质样品的温度历史研究 - 已演变为地球系统研究的基本部分。正如1970年代和1980年代的地球化学界引发了新同位素示踪剂的发展，作为地幔和地壳进化的探针，热量体学界现在正在迅速升高温度范围和温度历史重建的精度。这样的重建具有多种应用，以理解与社会相关的地球系统进化的各个方面。重建沉积盆地的热史对于我们确定石油和天然气潜力至关重要。更普遍地，我们知道，热历史是上皮中的岩石的，受侵蚀过程的强烈影响。这些过程反过来受到气候变化的影响，因此，低温热相理计（该研究项目的重点）已成为我们重建过去气候波动对数百万年时间尺度的主要手段。 这些信息对于我们建立长期气候变化至关重要，这可以帮助我们更好地将当前的气候趋势与地球历史上的人们进行比较，并更充分地评估气候极端变化的社会含义。矿物质系统用于热化学计的实际实用性受我们对氦扩散动力学知识的质量的限制。磷灰石和锆石的最新实验研究表明，辐射损伤基本影响了氦的扩散率。最近对锆石的研究表明氦扩散各向异性（平行于C晶体学方向的数量级）。研究人员提出了一项研究，旨在系统地量化这两种影响对（u-th）/HE热chronometry的氦延伸的影响：he thermochronometry：sonazite，金红石，钛铁矿，Xenotime和锆石。他们将通过热退火和质子照射来制备具有不同水平的辐射损伤的样品，以进行两种扩散实验：1）更熟悉的增量加热，大量扩散方法，通过这些方法获得了大多数当前可用的氦扩散数据； 2）一种新开发的激光消融深度分析方法，该方法能够在预定的晶体学方向中对实验室诱导的扩散谱进行询问。该项目的最终目标是为开发模式的开发做出贡献，以将适当的唯一扩散参数分配给单个晶体，以便themochonologister可以更自信地使用测量的日期进行热历史重建。