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

该项目研究天然晶体在化学平衡下生长的程度。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。这项研究检查了几个不同山脉的岩石，这些岩石在地质时期受到不同的压力和温度。该项目支持研究生和本科生的教育和培训，包括来自得不到充分服务群体的学生。此外，在研究过程中收集的样本是博伊西州立大学本科生课堂矿物学和岩石学练习的重点，该大学提供独特的学生人口统计（西班牙裔，归国和退伍军人学生的显着比例）。该项目的中心焦点是批判性地评估变质晶体在岩石中的化学平衡中大量生长的假设。一种新的方法，使用包裹体弹性热压恢复温度和压力独立的矿物化学。主要研究问题包括：（1）包裹体弹性压力法和温度法是否产生了与热力学方法显著不同的P-T路径？(2)包裹体弹性气压计和温度计是否意味着石榴石核的静态生长，甚至可能包括低级岩石中的整个晶体？(3)无论是在矩阵应变或在散装组合物，移动平衡石榴石生长到更高的温度减少的量的超越，石榴石核心的大小，并计算的P-T路径的偏差？分析包括四个不同的造山带的压力和温度的测量：北方阿巴拉契亚山脉，阿尔卑斯山脉中部，智利最南端，和喜马拉雅山脉中部/东部。结果广泛评估的频率和幅度的不平衡石榴石生长，以及温度和应变对石榴石成核的影响。该研究包括一名博士生和一名本科生，他们进行测量、解释数据、在国际会议上展示结果，并将结果撰写出版。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。

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.