Collaborative Research: Overstepping and the Formation of Metamorphic Garnet - Field, Laboratory, Geochronological, Experimental and Modeling Studies

合作研究：超越和变质石榴石的形成 - 现场、实验室、地质年代学、实验和建模研究

• 批准号: 2147527
• 负责人: Ethan Baxter
• 金额: $ 10.4万
• 依托单位: Boston College
• 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: 2022-02-01 至 2025-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2147527&HistoricalAwards=false
• 关键词: Collaborative; Research; Overstepping; Formation; Metamorphic

Metamorphism is the process by which sedimentary rocks are transported deep into the Earth to high pressures (P) and temperatures (T) conditions. Deep in the Earth, clay, sandstone, and limestone are transformed into crystalline metamorphic rocks like schists, quartzites, and marbles. Chemical reactions that transform sedimentary minerals into metamorphic minerals can also release fluids such as water (H2O) and carbon dioxide (CO2), originally trapped in the sedimentary minerals. These fluids have a major impact on earth processes such as the formation of volcanoes, the triggering of earthquakes, and the formation of valuable ore deposits. In addition, these fluids may make it to the Earth’s surface where they affect the climate. Over the last 50-60 years most scientists worked within the paradigm that metamorphism is a slow process, releasing fluids gradually over millions of years during mountain-building events. However, more recent work suggests that metamorphic processes may occur relatively rapidly in brief bursts that may occur over timescales of hundreds of thousands of years or less. The goal of this study is to test the more recent alternative hypothesis about rapid metamorphism. This study may shift longstanding interpretations that metamorphism occurs over very long timescales to a new paradigm of more rapid recrystallization, metamorphic mineral growth and release of fluids and has the potential to alter views on Earth processes. This work supports research opportunities and the training of postdocs and PhD students belonging to underrepresented groups. This grant will also contribute to a series of educational outreach videos on the YouTube channel “Every Rock Has A Story” that feature a diverse slate of co-hosts (e.g., kids, women, and scientists from underrepresented groups). “Every Rock Has A Story” brings to life the remarkable stories that exist inside every rock. When these stories are told by a diverse cast of co-hosts, kids see themselves as scientists and are inspired to explore the science of the Earth themselves.This proposal will investigate this alternative hypothesis — that rocks transform relatively rapidly with consequential relatively rapid release of fluids with a multi-pronged, multidisciplinary approach that includes field work, laboratory analysis, geochronology (dating mineral formation), high temperature-pressure experiments, and thermodynamic modeling of the nucleation and growth of the mineral garnet as a type example of metamorphic recrystallization. The field, laboratory and geochronological studies will focus on a comparison of rocks from the same outcrop that display numerous small garnets and few large garnets. Nucleation theory predicts that the number of new crystals (i.e. nuclei) that form under similar conditions is a function of the amount of overstepping of the equilibrium reaction (called the “affinity”). The pressure-temperature conditions of garnet formation will be determined from a combination of inclusion barometry using Raman spectroscopy and trace element thermometry (e.g., quartz or graphite-in-garnet; Zr in rutile thermometry) to see if garnets nucleated at consistent displacements from the equilibrium isograd for the bulk composition or whether they nucleated at similar P–T conditions, which would suggest significantly different degrees of overstepping at a common point of garnet nucleation. Ages of garnet formation using Sm-Nd geochronology will constrain whether garnets from both types of samples nucleated at different times consistent with the different locations of the equilibrium isograd, or as part of a single orogenic-scale nucleation event. Experiments at high pressures and temperatures will be conducted using piston-cylinder apparatus in order to determine (a) the location of the equilibrium garnet isograd for each specific rock composition and (b) the amount of overstepping of the isograd required to nucleate garnet as a function of the MnO content of the rock. This will provide experimental verification of the field studies and enable refinement of the thermodynamic properties of the Mn-component (spessartine) in garnet. Thermodynamic modeling of assemblage evolution in far-from-equilibrium assemblages will provide a basis for comparison with the natural parageneses and will refine our understanding of how metamorphic rocks evolve on a nano scale. The grant will also provide episode content and co-hosts for new episodes of “Every Rock Has A Story”, a YouTube series created by co-PI Ethan Baxter to engage and inspire elementary school age children about the geosciences. Rocks collected — or experimentally created — through the course of this research will be the centerpiece of some of the new episodes. Episodes will present the science through storytelling, designed to engage and inspire our young learners. Storytellers will include co-PI Baxter as well as other team members including women and underrepresented minorities to help more children see themselves as scientists.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.

变质是将沉积岩深入地球到高压（P）和温度（T）条件的过程。在地球深处，粘土，砂岩和石灰石被转化为晶状体，石英岩和大理石等结晶变质岩石。将沉积矿物转化为变质矿物的化学反应也可以释放出最初被困在沉积矿物质中的水（H2O）和二氧化碳（CO2）等液体。这些流体对地球过程有重大影响，例如火山的形成，地震的触发以及有价值的矿石沉积物的形成。此外，这些流体可能会使它们进入影响气候的地球表面。在过去的50 - 60年中，大多数科学家在范式中工作，即变质是一个缓慢的过程，在山区建设活动期间逐渐释放了数百万年的流体。但是，最近的工作表明，变质过程可能会在短暂的爆发中相对迅速发生，这可能发生在数十万年或更短的时间内。这项研究的目的是检验有关快速变质的最新替代假设。这项研究可能会改变长期的解释，即变质发生在很长的时间尺度上，以更快地重结晶，变质矿物的生长和流体释放的新范式，并有可能改变对地球过程的看法。这项工作支持研究机会以及属于代表性不足的小组的博士后和博士学位学生的培训。该赠款还将在YouTube频道“每个岩石都有一个故事”上为一系列教育外展视频做出贡献，该视频具有众多共同主持人的潜水员（例如，来自代表性不足的团体的孩子，妇女和科学家）。 “每个岩石都有一个故事”带来了每个岩石内部存在的非凡故事。当这些故事被一系列的共同主持人讲述时，孩子们将自己视为科学家，并受到启发来探索地球本身的科学。该提案将调查这一替代假设 - 岩石相对较快地转变为相对较快的流体，而相对较快地释放了多种多样的多学科，包括现场工作，实验室高温，较高的培训，逐渐养成的培训（均匀的培训）（有效的），并有效地释放，该假设相对较快。矿物石榴石成核和生长的热力学建模是变质重结晶的一种例子。该领域，实验室和年代学研究将集中于相同露头的岩石的比较，这些岩石显示出许多小石榴石和很少的大石榴石。成核理论预测，在相似条件下形成的新晶体（即核）的数量是平衡反应过度超平衡量的函数（称为“亲和力”）。 The pressure-temperature conditions of garnet formation will be determined from a combination of inclusion barometry using Raman spectroscopy and trace element thermometry (e.g., quartz or graphite-in-garnet; Zr in rutile thermometry) to see if garnets nuclearted at consistent displacements from the equilibrium isograd for the bulk composition or whether they nuclearted at similar P–T conditions, which would suggest significantly Different degrees of在石榴石核的一个公共点上踩踏。使用SM-ND年代学的石榴石形成的年龄将限制在两种样品中的石榴石是在不同时间核能与等效ISOGRAD的不同位置相一致的，还是作为单个造基尺度核事件的一部分。将使用活塞缸装置进行高压和温度下的实验，以确定（a）每个特定岩石组成的等效石榴石等值等等的位置，以及（b）核石榴石所需的同进量的量，核石榴石作为岩石MNO含量的功能。这将提供对现场研究的实验验证，并能够改进石榴石中MN组分（Spessartine）的热力学特性。远距离平衡组合中组合演化的热力学建模将为与天然旁皮的比较提供基础，并将完善我们对变质岩石如何在纳米尺度演化的理解。该赠款还将为“每个岩石都有故事”的新剧集提供情节内容和共同主持人，这是由Co-Pi Ethan Baxter创建的YouTube系列，旨在吸引和激发小学时代的孩子有关地球科学的孩子。通过这项研究的过程收集的岩石或实验创造的岩石将成为一些新情节的核心。情节将通过讲故事来展示科学，旨在吸引和启发我们的年轻学习者。讲故事的人将包括Co-Pi Baxter以及其他团队成员，包括妇女和代表性不足的少数群体，以帮助更多的孩子将自己视为科学家。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子的智力优点和更广泛的影响来通过评估来支持的。