CAREER: Is Continental Crust Juvenile or Reworked? A Test of Growth Models Using the Extant Neoarchean Granitoid Record

职业：大陆地壳是年轻的还是经过改造的？

• 批准号: 2145334
• 负责人: Jesse Reimink
• 金额: $ 90.32万
• 依托单位: Pennsylvania State Univ University Park
• 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: 2022-09-01 至 2027-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2145334&HistoricalAwards=false
• 关键词: CAREER; Continental; Crust; Juvenile; Reworked

There currently exist more geological samples from the Moon than from our own planet during the first 500 million years of the Solar System. This dearth of samples has led to vigorous debate amongst the geological community regarding three very important aspects of Earth evolution: 1) when, 2) how, and 3) to what extent did continents emerge on the early Earth. Recent advances in technical capabilities now allow these questions to be revisited. Earth is a tectonically active planet, which means that old rocks are constantly being altered, leaving few pristine samples from the earliest phases of Earth history. By looking for very small, but important isotopic signatures in preserved rock samples, one may infer how much continental crust was around very early in Earth history. This project will fund advanced isotopic analyses of ~2.6-billion-year-old rocks in a search of evidence for great than 4.0-billion-year-old continental material, material that may have been reworked during later tectonic events. Collection of this data will allow the research team to test the hypothesis that very large volumes of ancient continental crust existed on the early Earth and to answer a fundamental question about planetary formation and evolution – when did continental crust form on Earth? This project will also support an undergraduate field research experience, which will serve to train the next generation of geoscientists in skills that employers are keenly interested in – field geology and spatial reasoning skills.This proposal will combine petrology and isotope geochemistry to test broad hypotheses regarding the growth and reworking of continental crust. Neoarchean granitoid rocks represent some of the oldest well-preserved suites of rocks on Earth. Detailed analysis of samples will address the fundamental question of when continental crust formed on Earth. This proposal will analyze suites of granitoids from three distinct North American cratons for their igneous chemical signatures. Zircon age and isotopic information (U-Pb-Hf-O) will be measured from several compositional groups to test the fidelity of commonly used tracers for crustal melting and overprinting. Analyses of xenocrystic zircons and bulk rock Nd-isotope ratios will be used to search for reworking of truly ancient (4.0 Ga) crust in the Neoarchean—a time that has been suggested to have experienced broad overprinting of the continental record. The research team focus on 142Nd analyses as these data are particularly adept at identifying Hadean crustal relics. This proposal will fund an REU field experience aimed at developing a diverse and strategically important workforce with training in field geology and spatial reasoning. The maps created and samples collected by undergraduate researchers will be used for advanced isotopic analyses conducted during the scientific study, and undergraduate participants will not only gain important—and in-demand—skills in spatially-focused critical thinking but will also be exposed to advanced geochemical techniques and datasets. These participants will finish their undergraduate experience well positioned to pursue many types of careers in the geosciences.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.

目前，来自月球的地质样本比太阳系成立前5亿年来自我们星球的地质样本还多。由于缺乏样品，地质界就地球演化的三个非常重要的方面展开了激烈的辩论：1)大陆何时出现，2)如何形成，3)大陆在早期地球上出现的程度如何。最近在技术能力方面的进步使这些问题得以重新讨论。地球是一个构造活跃的行星，这意味着古老的岩石正在不断地发生变化，留下的地球历史早期阶段的原始样本很少。通过在保存下来的岩石样本中寻找非常小但重要的同位素特征，可以推断出地球历史上很早就有多少陆壳存在。该项目将资助对大约26亿年前的岩石进行先进的同位素分析，以寻找超过40亿年的大陆物质的证据，这些物质可能在后来的构造事件中进行了重新加工。收集这些数据将使研究小组能够检验早期地球上存在大量古代陆壳的假设，并回答关于行星形成和演化的一个基本问题--地球上的陆壳是什么时候形成的？这个项目还将支持本科生的实地研究经验，这将有助于培训下一代地球科学家的技能，使他们掌握雇主最感兴趣的技能--实地地质学和空间推理技能。这项提议将把岩石学和同位素地球化学结合起来，检验有关陆壳生长和改造的广泛假设。新太古代花岗岩代表了地球上最古老、保存最完好的一套岩石。对样品的详细分析将解决大陆地壳在地球上形成的根本问题。这项提议将分析来自北美三个不同克拉通的花岗岩套，以寻找它们的火成岩化学特征。将从几个成分组测量锆石年龄和同位素信息(U-Pb-Hf-O)，以测试用于地壳熔融和叠印的常用示踪剂的保真度。对包裹体锆石和块状岩石的分析将被用来寻找新太古代真正古老(4.0Ga)地壳的改造--这段时间被认为经历了大陆记录的广泛叠加。研究小组将重点放在第142次分析上，因为这些数据特别擅长识别赫甸地壳遗迹。这项提议将为区域联盟实地经验提供资金，旨在通过实地地质学和空间推理方面的培训，培养一支具有战略重要性的多样化劳动力队伍。本科生研究人员创建的地图和收集的样本将用于在科学研究期间进行高级同位素分析，本科生参与者不仅将在专注于空间的批判性思维方面获得重要和急需的技能，还将接触到先进的地球化学技术和数据集。这些参与者将完成他们的本科经历，为在地球科学领域从事多种类型的职业做好准备。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。