A macro- to nano-scale interrogation of 4 Gyr of tectonism, metamorphism and alteration in the Acasta Gneiss Complex

对阿卡斯塔片麻岩杂岩 4 Gyr 的构造作用、变质作用和蚀变进行宏观到纳米尺度的研究

• 批准号: 2136782
• 负责人: Tyler Blum
• 金额: $ 46.53万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-05-01 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2136782&HistoricalAwards=false
• 关键词: macro; nano; scale; interrogation; Gyr

The origin and growth of continental crust on Earth is an important and enduring question in the Earth sciences. The configuration and interaction of tectonic plates throughout Earth’s history is recognized to play a critical role in Earth’s crustal evolution. The Acasta Gneiss Complex (AGC) of the Northwest Territories, Canada, exposes the oldest known continental crustal rocks. This project will characterize the detailed geochemistry of an important mineral, zircon, in the AGC to evaluate the role of plate tectonic style (“stagnant-lid” vs. “mobile-lid”) in continent formation. Ratios of trace elements and isotopes in zircon will allow the PIs to track changes in AGC crustal compositions over the course of approximately 1 billion years of Earth’s history, starting 4 billion years ago. Because of their extreme age, AGC zircon grains accumulate damage to the crystal structure over geologic time. As a result, many (though not all), zircon grains in Acasta have had their age and chemistry altered. This work combines diverse methods of imaging, mass spectrometry and structural characterization of zircon, allowing the PIs to identify unaltered zircon chemistries and to evaluate the timing of alteration processes. Results of the characterization of zircon will also provide information about changes in continental crustal production and links between tectonic style and the formation of the oldest continents on Earth. This research will also support community outreach in collaboration with the University of Wisconsin Geology Museum to improve scientific literacy and expand the public’s understanding of geologic time.The 4 to 3 Ga Acasta Gneiss Complex (AGC), Canada, comprises over one billion years of magmatism, including the oldest known exposures of felsic terrestrial crust, and thereby is a critical archive of early terrestrial differentiation. The mineral zircon has been invaluable for tracking the chronology and sources of magmatism in the AGC; however, pervasive alteration of age, trace element, and isotope chemical information (often related to radiation-damage-induced loss of crystallinity and recrystallization) has impaired efforts to construct robust U-Pb geochronological, δ18O, and trace element records spanning the duration of AGC magmatism. This work will apply a novel and diverse set of characterization methods (plasma and secondary ion mass spectrometry, Raman spectroscopy, and atom probe tomography) to: 1) expand the primary U-Pb isotope, δ18O, and trace element record for AGC zircon grains in tandem with the whole-rock geochemical record, including tectonic provenance proxies Sc and Nb as well as alteration proxy OH in zircon; and 2) interrogate the grain-scale to nanoscale manifestations of repeated thermal events and fluid interactions within zircon grains by atom probe tomography. Ultimately, the work will clarify primary versus secondary zircon chemistry, the length scales of element mobility during a multistage thermal and metamorphic history, and the primary 4-3 Ga magmatic and tectonic history of the AGC. This research will also support community outreach in collaboration with the University of Wisconsin Geology Museum to improve scientific literacy and expand the public’s understanding of geologic time.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.

地球上大陆地壳的起源和生长是地球科学中一个重要且持久的问题。整个地球历史上构造板块的构造和相互作用被认为在地球地壳演化中发挥着关键作用。加拿大西北地区的阿卡斯塔片麻岩杂岩体 (AGC) 暴露出已知最古老的大陆地壳岩石。该项目将描述 AGC 中重要矿物锆石的详细地球化学特征，以评估板块构造类型（“静止盖”与“移动盖”）在大陆形成中的作用。锆石中微量元素和同位素的比率将使 PI 能够追踪从 40 亿年前开始的地球历史中大约 10 亿年的 AGC 地壳成分的变化。由于其极端年龄，AGC 锆石晶粒随着地质时间的推移，晶体结构逐渐受到损害。结果，阿卡斯塔中的许多（尽管不是全部）锆石颗粒的年龄和化学成分都发生了变化。这项工作结合了锆石的多种成像、质谱和结构表征方法，使 PI 能够识别未改变的锆石化学成分并评估改变过程的时间。锆石表征的结果还将提供有关大陆地壳生产变化以及构造风格与地球上最古老大陆形成之间联系的信息。这项研究还将与威斯康星大学地质博物馆合作支持社区外展活动，以提高科学素养并扩大公众对地质时间的理解。加拿大 4 至 3 Ga 阿卡斯塔片麻岩杂岩 (AGC) 包含超过 10 亿年的岩浆作用，包括已知最古老的长英质地壳暴露，因此是早期陆地分化的重要档案。矿物锆石对于追踪 AGC 中岩浆作用的年代和来源具有不可估量的价值。然而，年龄、微量元素和同位素化学信息的普遍改变（通常与辐射损伤引起的结晶度和重结晶损失有关）削弱了构建跨越 AGC 岩浆作用期间的可靠 U-Pb 地质年代学、δ18O 和微量元素记录的努力。这项工作将应用一套新颖且多样化的表征方法（等离子体和二次离子质谱、拉曼光谱和原子探针断层扫描）来：1）将 AGC 锆石颗粒的主要 U-Pb 同位素、δ18O 和微量元素记录与全岩石地球化学记录相结合，包括构造物源代理 Sc 和 Nb 以及蚀变代理 OH 锆石； 2）通过原子探针断层扫描研究锆石晶粒内重复热事件和流体相互作用的晶粒尺度到纳米尺度的表现。最终，这项工作将阐明原生与次生锆石化学、多阶段热和变质历史期间元素迁移率的长度尺度，以及 AGC 的原生 4-3 Ga 岩浆和构造历史。这项研究还将与威斯康星大学地质博物馆合作支持社区外展活动，以提高科学素养并扩大公众对地质时代的理解。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。

项目成果

Mechanisms for generating elevated zircon δ18O in Archean crust: Insights from the Saglek-Hebron Complex, Canada

太古代地壳中生成高位锆石 δ18O 的机制：来自加拿大萨格莱克-希伯伦杂岩的见解

• DOI: 10.1016/j.epsl.2023.118443
• 发表时间: 2023
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Mixon, Emily E.;Bauer, Ann M.;O'Neil, Jonathan;Rizo, Hanika;Blum, Tyler B.;Valley, John W.;Bonamici, Chloë E.
• 通讯作者: Bonamici, Chloë E.

Evidence for Oceans pre-4300 Ma Confirmed by Preserved Igneous Compositions in Hadean Zircon

• DOI: 10.2138/am-2023-9180
• 发表时间: 2024-03
• 期刊: American Mineralogist
• 影响因子: 3.1
• 作者: Emilia M. Cameron;Tyler Blum;A. Cavosie;K. Kitajima;Lutz Nasdala;I. Orland;C. Bonamici;J. Valley