Does deformation lead to misinformation? How much can granitic rocks deform before accessory minerals are geochemically disturbed?

变形会导致错误信息吗？

• 批准号: 2342159
• 负责人: Johannes Haemmerli
• 金额: $ 46.87万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-05-15 至 2027-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2342159&HistoricalAwards=false
• 关键词: Does; deformation; lead; misinformation; How

How Earth’s early crust formed and evolved is one of the most debated questions in Earth Science. A major problem is that all of these ancient rocks have experienced at least one episode of alteration, deformation and/or metamorphism. So no pristine rocks (protoliths) exist. However, many studies have used whole rock geochemistry and isotope tracers, and more recently the isotope signatures of accessory phases as important anchor points for models of how the crust has evolved and grown over time. Various theories and processes have been proposed for the formation of Earth's earliest stable crust. The debate over interpreting these data revolves around a core inquiry: whether the deformation and metamorphism of crustal rocks alters certain geochemical markers commonly used in reconstructing crustal history. The primary goal of this study is to test the hypothesis that certain elements and isotopes in deformed (ancient) rocks accurately reflect the original geochemical signatures of their protolith. This hypothesis will be tested by evaluating if the isotope signatures of whole rock and accessory minerals remain unchanged with increasing strain, and hence faithfully record the original protolithic (isotope) composition, or if deformation leads to the disturbance of isotope systems on a mineral and/or whole rock scale. Three different sequences of rocks, varying in degrees of deformation, will be studied to understand the extent to which deformation may alter their geochemical signatures on a whole rock, and (sub)-mineral-scale. These sequences range from initially undeformed (protolith) rocks to highly deformed ones, which closely resemble the world's oldest rocks. The findings of this study will help researchers use and interpret geochemical, particularly isotopic, data from deformed ancient rocks. This research will support student training, international collaboration, and continued development of analytical facilities at the Peter Hooper GeoAnalytical Lab and the Radiogenic Isotope & Geochronology Lab at Washington State University. Two PhD students (one female), as well as undergraduate students will be trained in field work and cross-disciplinary research spanning from mineralogy to structural geology to geochemistry.Isotope signatures in whole rock samples and in some accessory minerals, such as zircon, apatite, allanite, and titanite, are frequently used to reconstruct the formation and evolution of the Earth’s crust. However, virtually all Archean and Proterozoic rocks have experienced one or more episodes of deformation and metamorphism following their emplacement, and it is unclear to what degree these rocks retain their original (i.e., protolithic) isotope ratios after experiencing these tectono-thermal events. This research combines a geochemical and structural approach to understand to what degree granitic rocks can be deformed without changing their protolithic geochemical fingerprint at a whole rock- and (sub-)mineral-scale. This project will focus on testing a primary hypothesis: that whole rocks and accessory minerals in variably deformed granitic rocks faithfully retain their original geochemical isotope signatures and hence can be used to reconstruct long-term crustal processes, such as the formation of Earth’s earliest stable crust. The following key questions will be investigated: 1) what accessory minerals are involved in deformation-induced mineral reactions? 2) does deformation lead to open-system processes, and if so, how does this vary with degree of deformation? and 3) to what extent do Lu-Hf, Sm-Nd, and Rb-Sr isotope systematics in accessory minerals of variably deformed rocks faithfully preserve their initial isotope compositions? Three different field localities in which the same granitic bodies are exposed across strain gradients, spanning from undeformed to highly deformed will be studied. Via comparison of isotope data of the above systems on an accessory mineral- and whole rock-scale between deformed granitic rocks and their protoliths can be tested if deformed rocks retain their original isotope signatures on different scales (mineral vs. whole rock) or if the above isotope systems become disturbed upon deformation and hence cannot be trusted to reflect the protolithic composition. High-spatial resolution in-situ isotope and elemental analyses via EPMA and LA-(MC)-ICP-MS will be conducted on all major and accessory phases in order to gain an in-depth understanding of how minerals geochemically communicate with each other during deformation and if and to what degree trace elements are mobilized and redistributed on different scales. The results of this study will offer key understandings into how geochemical and particularly isotopic information from deformed and metamorphosed rocks can be interpreted and applied to reconstruct large-scale crustal processes.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.

地球早期的地壳如何形成和进化是地球科学中最讨论的问题之一。一个主要的问题是，所有这些古老的岩石至少经历了一集的变化，变形和/或变质。因此，不存在原始岩石（原始岩石）。但是，许多研究都使用了整个岩石地球化学和同位素示踪剂，最近，附件阶段的同位素特征是地壳如何随着时间而发展和生长的重要锚点。已经提出了各种理论和过程，以形成地球最早的稳定地壳。解释这些数据的辩论围绕着核心查询：地壳岩石的变形和变质性是否改变了重建地壳历史中常用的某些地球化学标记。这项研究的主要目的是检验以下假设：变形（古代）岩石中的某些元素和同位素准确反映其原始的原始地球化学特征。该假设将通过评估整个岩石和辅助矿物的同位素特征是否随着应变的增加而保持不变，从而忠实地记录原始原石（同位素）组成，或者是否会导致矿物和/或整个岩石尺度上的同位素系统灾难。将研究三个不同的岩石序列，随着变形的程度不同，以了解变形可能在多大程度上改变其在整个岩石上的地球化学特征，以及（子） - 矿物质尺度。这些序列范围从最初未构造的（原始石）到高度变形的岩石，它们与世界上最古老的岩石非常相似。这项研究的结果将帮助研究人员使用和解释来自变形的古岩石的地球化学，特别是同位素的数据。这项研究将支持在彼得·胡珀（Peter Hooper）地理分析实验室和华盛顿州立大学的放射性同位素和地球体学实验室的学生培训，国际合作以及持续开发分析设施。两名博士学位学生（一名女）以及本科生将接受野外工作和跨学科研究的培训，从矿物学到结构地质学到地球化学。整个岩石样本中的同位素签名以及某些附件矿物，例如锆石，磷灰石，apatite，allanite，allanite和titanium，经常用于整理和titeration crust and crust the Arcortoral和crust crust and Crust and Crust。但是，实际上，所有的大古岩和原始岩石都经历了一个或多种变形和变质的发作，并且在经历了这些textono-thermal-thermal-thermal-thermal-thermal-thermal事件后，这些岩石在多大程度上保留了它们的原始（即原石）同位素比的程度。这项研究结合了一种地球化学和结构方法，以了解如何变形花岗岩岩石。在整个岩石和（亚）矿物尺度上，没有更改其质石化的地球化学指纹。该项目将着重于测试主要假设：在多样化变形的花岗岩岩石中，整个岩石和附件矿物质忠实地保留了其原始的地球化学同位素特征，因此可以用于重建长期的地壳过程，例如地球最早的稳定硬皮的形成。将研究以下关键问题：1）变形引起的矿物反应涉及哪些辅助矿物？ 2）变形会导致开放系统过程，如果是的，则随着变形程度如何变化？ 3）LU-HF，SM-ND和RB-SR同位素系统在多大程度上忠实地保留其初始同位素组成的辅助矿物质中？三个不同的田间位置，其中相同的花岗岩物体在跨应变梯度之间暴露在未形成到高度变形的应变梯度之间。通过比较上述系统的同位素数据，如果变形的岩石保留其原始的同位素签名（矿物质与全岩），或者上述同位素系统会因变形和构成蛋白石的构成，则可以测试在变形的花岗岩岩石及其原石之间的附件矿物和整个岩石尺度上。通过EPMA和LA-（MC）-ICP-MS进行高空间分辨率的原位同位素和元素分析，将在所有主要和附件阶段进行，以深入了解矿物在变形期间以及程度的痕量元素如何在变形过程中以及在不同量表上进行了痕量轨迹元素在变形时如何相互交流。这项研究的结果将对来自变形和变质岩石中的地球化学，尤其是同位素信息的关键理解可以解释并应用于重建大规模的地壳过程。该奖项反映了NSF的法定任务，并通过基金会的知识优点和广泛的影响来评估NSF的法定任务，并被认为是诚实的支持。