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，月球上的地质样本比太阳系前5亿年的地球上的还要多。样品的缺乏导致地质学界对地球演化的三个非常重要的方面进行了激烈的辩论：1）何时，2）如何以及3）在何种程度上大陆在早期地球上出现。技术能力的最新进展现在使人们能够重新审视这些问题。地球是一个构造活跃的星球，这意味着古老的岩石不断被改变，几乎没有留下地球历史最早阶段的原始样本。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，人们可以推断在地球历史的早期有多少大陆地壳。该项目将资助对26亿年前的岩石进行先进的同位素分析，以寻找40亿年前大陆物质的证据，这些物质可能在后来的构造事件中被改造。这些数据的收集将使研究小组能够测试早期地球上存在大量古代大陆地壳的假设，并回答有关行星形成和演化的一个基本问题-大陆地壳何时在地球上形成？该项目还将支持本科生实地研究经验，这将有助于培养下一代地球科学家的技能，雇主非常感兴趣的-实地地质学和空间推理技能。该提案将结合联合收割机岩石学和同位素地球化学，以测试有关大陆地壳生长和改造的广泛假设。新太古代花岗岩类岩石代表了地球上一些最古老的保存完好的岩石套件。对样品的详细分析将解决大陆地壳何时在地球上形成的基本问题。 该提案将分析来自三个不同的北美花岗岩类的火成岩化学签名套件。 锆石年龄和同位素信息（U-Pb-Hf-O）将从几个组成组进行测量，以测试地壳熔融和叠印常用示踪剂的保真度。捕虏晶锆石和散装岩石钕同位素比值的分析将被用来寻找真正古老的（4.0 Ga）地壳在新太古代的改造，已被认为经历了广泛的大陆记录的叠印时间。 研究小组专注于142Nd分析，因为这些数据特别擅长识别Hadean地壳遗迹。该提案将资助REU实地经验，旨在培养一支多样化和具有战略重要性的劳动力队伍，并接受实地地质学和空间推理方面的培训。 由本科生研究人员创建的地图和收集的样本将用于科学研究期间进行的高级同位素分析，本科生参与者不仅将获得以空间为重点的批判性思维方面的重要技能，而且还将接触到先进的地球化学技术和数据集。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。