Reevaluation of metamorphic garnet-based P-T paths and their tectonic implications

这个项目研究的是天然晶体在化学平衡中的生长程度。这些信息是研究变质岩的核心，特别是它们形成时的压力和温度。这项研究考察了几个不同山脉地带的岩石，这些岩石在地质时期受到不同的压力和温度。该项目支持对研究生和本科生的教育和培训，包括来自贫困群体的学生。此外，在研究期间收集的样本是博伊西州立大学本科生矿物学和岩石学练习的重点，该大学服务于独特的学生群体(西班牙裔学生、归国学生和退伍军人学生的比例相当高)。这个项目的中心焦点是批判性地评估变质晶体在岩石中脱离化学平衡而生长的假说。应用包裹体弹性温压计恢复温度和压力的新方法不依赖于矿物化学。三个主要的研究问题包括：(1)与基于热力学的方法相比，包裹体弹性压力法和测温法是否产生显著不同的P-T路径？(2)包裹体弹性压力法和测温法是否意味着石榴石核的静态生长，甚至包括低品位岩石中的整个晶体？(3)将平衡石榴石生长转移到更高温度的基质应变或块体成分的差异是否会减少跳跃量、石榴石核的大小以及对计算的P-T路径的偏差？分析包括对四个不同造山带的压力和温度的测量：阿巴拉契亚山脉北部、阿尔卑斯山中部、智利最南端和喜马拉雅中部/东部。结果广泛地评价了石榴石不平衡生长的频率和程度，以及温度和应变对石榴石成核的影响。这项研究包括一名博士生和本科生进行测量，解释数据，在国际会议上展示结果，并将结果撰写发表。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project investigates the degree to which natural crystals grow in chemical equilibrium. This information is central to the study of metamorphic rocks, especially the pressures and temperatures at which they form. The research examines rocks from several different mountain belts that have been subjected to different pressures and temperatures through geologic time. The project supports the education and training of graduate and undergraduate students, including students from underserved groups. In addition, samples collected during the research are the focus of undergraduate in-class mineralogy and petrology exercises at Boise State University, which serves an unique student demographic (significant percentages of Hispanic, returning, and veteran students). The central focus of this project is to critically evaluate the hypothesis that metamorphic crystals grow substantially out of chemical equilibrium in a rock. A novel approach using inclusion elastic thermobarometry is applied to recover temperature and pressure independent of mineral chemistry. Three main research questions include: (1) Does inclusion elastic barometry and thermometry yield significantly different P-T paths compared to thermodynamically-based methods? (2) Does inclusion elastic barometry and thermometry imply static growth of garnet cores, perhaps even encompassing entire crystals in low-grade rocks? (3) Do differences either in matrix strain or in bulk compositions that shift equilibrium garnet growth to higher temperatures reduce the amount of overstepping, the size of garnet cores, and the bias to calculated P-T paths? Analyses include measurements of pressure and temperature for four different orogenic belts: the northern Appalachians, central Alps, southernmost Chile, and central/eastern Himalaya. Results broadly evaluate the frequency and magnitude of disequilibrium garnet growth, as well as the effects of temperature and strain on garnet nucleation. This research includes a PhD student and undergraduate students to make measurements, interpret data, present results at international meetings, and write up results for publication.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.