Collaborative Research: Experimental deformation of monazite and titanite: Implications for interpretation of petrochronologic data

合作研究：独居石和钛矿的实验变形：对岩石年代学数据解释的启示

• 批准号: 2217836
• 负责人: James Hirth
• 金额: $ 36.83万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2217836&HistoricalAwards=false
• 关键词: Collaborative; Research; Experimental; deformation; monazite

The deformation behavior of rocks controls the strength of the lithosphere, the location and intensity of earthquakes, the response of Earth to impact events, and the concentration and deposition of ore minerals. To understand the conditions and duration under which rocks deformed in the geologic past, and to improve understanding of earthquake processes, mineral resource identification, and crustal strength modelling, we will conduct a series of experiments on minerals important for geologic age dating. These deformation experiments will be conducted at conditions which simulate environments deep within the Earth’s crust. The principal investigators will fabricate synthetic rock samples embedded with natural mineral grains and use a rock deformation apparatus to impose high stress and strain conditions typical of deep Earth shear zones. The experiments will focus on the deformation behavior of accessory phase minerals titanite and monazite, which are routinely used for petrochronology, a technique which uses radiometric age dating to determine the timing of ancient metamorphic reactions and deformation events. The deformation behavior of the major rock-forming minerals (e.g., quartz, feldspar, olivine) has been well-studied, but our experiments will be among the first to investigate the deformation behavior of accessory phase minerals. Accessory phase minerals, such as monazite, are reservoirs for Rare Earth Elements (REEs) and the results of our experiments will provide better understanding of REE mobilization within fault zones. Societal benefits of the project include direct training of graduate and undergraduate students and a postdoctoral researcher in experimental and analytical skills that are valuable in many high-level government, defense, and industrial laboratories. Outreach efforts will involve developing earth science curricula for Providence, RI elementary school. The Department of Earth, Environmental and Planetary Sciences at Brown has an active outreach program known as the Science-Teaching and Education Program (STEP), which partners with local teachers to develop earth science modules in their classes. The project will also contribute to the broadening of underrepresented groups in STEM. The goal of this project is to experimentally deform a selection of accessory phase minerals and use multiple advanced microanalytical techniques to examine how various deformation and recrystallization mechanisms affect the distribution of elements and isotopes important for geochronology. The researchers will conduct a multi-step experimental protocol consisting of deformation in a Griggs-rig solid medium deformation apparatus followed by high temperature static annealing of a subset of samples. Accessory phases monazite and titanite with well-characterized trace element contents will be embedded as porphyroclasts in a matrix of quartz, synthetic quartz, or feldspar and deformed under prescribed temperatures, pressures, and strain rate conditions. Multiple advanced analytical techniques will allow us to investigate the composition and structure of deformed samples from the aggregate to atomic scale. The principal investigators will quantify the influence of lattice defects on the mobility of impurity elements and consequences of recrystallization for interpreting the geochemistry of deformed minerals. Our results will provide fundamental constraints on the rheological behavior of accessory phase minerals and enable more confident applications of accessory phase geochronology and geothermometry to deformed rocks.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.

岩石的变形行为控制着岩石圈的强度、地震的位置和强度、地球对撞击事件的响应以及矿石矿物的富集和沉积。为了了解过去地质时期岩石变形的条件和持续时间，并提高对地震过程、矿产资源识别和地壳强度建模的认识，我们将对对地质年龄测定重要的矿物进行一系列实验。这些变形实验将在模拟地壳深处环境的条件下进行。主要研究人员将制造嵌入天然矿物颗粒的合成岩石样品，并使用岩石变形装置施加地球深层剪切带典型的高应力和应变条件。这些实验将重点研究副相矿物钛矿和独居石的变形行为，这些矿物通常用于岩石年代学，这是一种利用放射性年龄测定来确定古代变质反应和变形事件时间的技术。主要造岩矿物（例如石英、长石、橄榄石）的变形行为已得到充分研究，但我们的实验将是第一个研究副相矿物变形行为的实验。独居石等副相矿物是稀土元素 (REE) 的储库，我们的实验结果将有助于更好地了解断层带内 REE 的流动。该项目的社会效益包括直接培训研究生和本科生以及博士后研究员的实验和分析技能，这些技能对于许多高级政府、国防和工业实验室都很有价值。外展工作将包括为罗德岛州普罗维登斯小学开发地球科学课程。布朗大学地球、环境和行星科学系有一个积极的外展计划，称为科学教学和教育计划 (STEP)，该计划与当地教师合作，在课堂上开发地球科学模块。该项目还将有助于扩大 STEM 中代表性不足的群体。该项目的目标是通过实验使精选的副相矿物变形，并使用多种先进的微分析技术来研究各种变形和再结晶机制如何影响对地质年代学重要的元素和同位素的分布。研究人员将进行多步骤实验方案，包括在 Griggs-rig 固体介质变形装置中变形，然后对一部分样品进行高温静态退火。具有充分表征的微量元素含量的副相独居石和钛矿将作为碎卟啉嵌入石英、合成石英或长石基质中，并在规定的温度、压力和应变率条件下变形。多种先进的分析技术将使我们能够研究从聚集到原子尺度的变形样品的成分和结构。主要研究人员将量化晶格缺陷对杂质元素迁移率的影响以及再结晶的后果，以解释变形矿物的地球化学。我们的研究结果将为副相矿物的流变行为提供基本约束，并使副相地质年代学和地温测量学更自信地应用于变形岩石。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。