CAREER: Rates and Timescales of Metamorphic Reactions at Convergent Plate Boundaries

职业：会聚板块边界处的变质反应的速率和时间尺度

• 批准号: 0547999
• 负责人: Ethan Baxter
• 金额: $ 50.45万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-01-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0547999&HistoricalAwards=false
• 关键词: CAREER; Rates; Timescales; Metamorphic; Reactions

Modern research and teaching in the earth sciences must include an increased awareness of the rates and timescales of geologic processes. Frontier research in plate boundary processes involves modeling of the production, consumption, and transport of fluids, as well as the evolving physical properties of the solid earth. Metamorphic reactions are at the roots of these processes. Model predictions of subduction zone processes require quantification of the rate and timescale over which metamorphic reactions in the crust and mantle proceed. However, in light of field-based and lab-based studies which differ in their kinetic predictions by many orders of magnitude, a lack of consensus exists regarding the rates most applicable to natural systems. Intellectual Merit: This proposal will address this fundamental need for field-based quantification of metamorphic reaction rates and timescales, with an emphasis on mineral transformations and volatile release in subduction zones. The approach involves the integration of three existing methodologies: 1) precise Sm/Nd geochronology of zoned garnets, 2) thermodynamic and modal analysis of zoned garnets, 3) modeling of reactive transport in layered rock systems to evaluate relative rates of reaction and transport. The main focus will be on garnet-forming dehydration reactions which occur in a wide variety of tectonic and lithologic settings. Isotopic (i.e. age) microsampling within zoned garnets will be provided using the recent joint NSF-Boston University TIMS/MicroMill Facility at BU under the directorship of the PI. The analytical mission of this facility, to push the limits of analytical precision and small sample size, is perfectly suited to the needs of the proposed research. The combined methodology will be applied to well-studied garnets from New England representing a regional metamorphic setting. Garnets from subduction zone settings (i.e. blueschist or low-T eclogite) will be sampled and analyzed similarly with the goal of developing a rate law for subduction zone mineral reactions and volatile release.Broader Impacts: It is important to infuse high school and undergraduate experiences with an appreciation of the exciting quantitative aspects of Earth Science, exemplified by the research described here. The education plan centers around a community outreach program called 'Rocks Beneath Our Toes' or RoBOT, integrated with undergraduate teaching and research. RoBOT engages Boston area high school students in the selection and sampling of rockoutcrops in their own communities, which should enhance their level of interest and sense of connection to the RoBOT program. Undergraduate mineralogy students will complete semester-long research projects on these and other samples from their own field trip. The RoBOT program culminates with a visit by high school students to BU to tour the TIMS Facility, use the microscopes in small breakout groups led by undergraduates, and hear the undergraduates' final reports. This outreach program gives all students the chance to share in the excitement of discovery-based learning while gaining an appreciation of frontier research in geochemistry. Outstanding undergraduates coming from the RoBOT experience would be tapped each year to help establish and maintain a synergistic research team. The research plan is rich with opportunities for undergraduates including field experience in New England or abroad within the context of the broader research goals. The proposal will support 2 graduate students who will be responsible for conducting the bulk of the research activities, while mentoring the undergraduates.

地球科学的现代研究和教学必须包括提高对地质过程的速率和时间尺度的认识。板块边界过程的前沿研究涉及流体的产生、消耗和传输以及固体地球不断变化的物理特性的建模。变质反应是这些过程的根源。俯冲带过程的模型预测需要量化地壳和地幔中变质反应进行的速率和时间尺度。然而，鉴于基于现场和基于实验室的研究其动力学预测存在多个数量级的差异，因此对于最适用于自然系统的速率缺乏共识。智力价值：该提案将解决变质反应速率和时间尺度的现场量化的基本需求，重点是俯冲带的矿物转化和挥发物释放。该方法涉及三种现有方法的整合：1) 分区石榴石的精确 Sm/Nd 地质年代学，2) 分区石榴石的热力学和模态分析，3) 层状岩石系统中反应输运的建模，以评估反应和输运的相对速率。主要关注点是在各种构造和岩性环境中发生的石榴石形成脱水反应。分区石榴石内的同位素（即年龄）微量采样将使用最近在 BU 的 NSF-波士顿大学 TIMS/MicroMill 联合设施在 PI 的领导下提供。该设施的分析任务是突破分析精度和小样本量的极限，完全适合拟议研究的需求。综合方法将应用于经过深入研究的代表区域变质环境的新英格兰石榴石。来自俯冲带环境（即蓝片岩或低 T 榴辉岩）的石榴石将进行类似的采样和分析，目的是制定俯冲带矿物反应和挥发物释放的速率定律。更广泛的影响：注入高中和本科生的经验非常重要欣赏地球科学令人兴奋的定量方面，这里描述的研究就是例证。该教育计划以名为“Rocks Beneath Our Toes”（RoBOT）的社区外展计划为中心，与本科生教学和研究相结合。 RoBOT 让波士顿地区的高中生参与自己社区中岩石露头的选择和采样，这应该会增强他们对 RoBOT 项目的兴趣和联系感。矿物学本科生将根据自己实地考察的这些样品和其他样品完成为期一个学期的研究项目。机器人项目的高潮是高中生访问 BU，参观 TIMS 设施，在由本科生带领的小组中使用显微镜，并听取本科生的期末报告。这个推广计划让所有学生都有机会分享基于发现的学习的兴奋，同时获得对地球化学前沿研究的欣赏。每年都会选拔具有机器人经验的优秀本科生来帮助建立和维持一个协同研究团队。该研究计划为本科生提供了丰富的机会，包括在更广泛的研究目标背景下在新英格兰或国外的实地经验。该提案将支持两名研究生，他们将负责开展大部分研究活动，同时指导本科生。