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

岩石的变形行为控制着岩石圈的强度、地震的位置和强度、地球对撞击事件的反应以及矿石的集中和沉积。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理解，我们将对地质年龄定年的重要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，并使用岩石变形设备施加典型的深部地球剪切带的高应力和应变条件。实验将重点关注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，这是一种使用放射性年龄测年来确定古代变质反应和变形事件的时间的技术。主要造岩矿物（如石英、长石、橄榄石）的变形行为已经得到了很好的研究，但我们的实验将是第一批研究副相矿物变形行为的实验之一。副相矿物，如独居石，是稀土元素（REE）的储集层，我们的实验结果将有助于更好地理解断裂带内稀土元素的运移。该项目的社会效益包括直接培养研究生和本科生以及博士后研究人员的实验和分析技能，这些技能在许多高级政府、国防和工业实验室都很有价值。外展工作将包括为国际扶轮普罗维登斯小学发展地球科学课程。布朗大学的地球、环境和行星科学系有一个积极的推广项目，被称为科学教学和教育项目（STEP），该项目与当地教师合作，在他们的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变形选择附属相矿物，并使用多种先进的微量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。研究人员将进行一个多步骤的实验方案，包括在格里格斯钻机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。辅助相独居石和钛矿具有明确的微量元素含量，将作为卟啉碎屑嵌入石英、合成石英或长石基质中，并在规定的温度、压力和应变速率条件下变形。多种先进的分析技术将使我们能够研究从聚集体到原子尺度的变形样品的组成和结构。主要研究人员将量化晶格缺陷对杂质元素迁移率的影响和再结晶的后果，以解释变形矿物的地球化学。我们的研究结果将为辅助相矿物的流变行为提供基本约束，并使辅助相地质年代学和地温学更有信心地应用于变形岩石。该奖项反映了美国国家科学基金会的法定使命，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。

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.