CAREER: Field Studies of Precambrian Impacts and Implications for the Early Crust and Environment

职业：前寒武纪影响及其对早期地壳和环境的影响的实地研究

• 批准号: 1352095
• 负责人: Alexandra Davatzes
• 金额: $ 44.54万
• 依托单位: Temple University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-02-01 至 2020-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1352095&HistoricalAwards=false
• 关键词: CAREER; Field; Studies; Precambrian; Impacts

Two geologic processes fundamentally shaped the early history of the Earth: large, frequent meteor impacts, and formation of crustal material and initiation of plate tectonics. The larger and more frequent impacts to the early Earth would have significantly affected the atmosphere, oceans and surface of the planet. Many of these impacts vaporized the top several meters of ocean water world-wide, excavated and vaporized rock as deep as the upper mantle, and occurred at a frequency that ensured that they influenced the early evolution of life. More than 10 large impacts from 3,500 to 2,400 million years ago excavated different parts of the crust into the upper mantle, and the vaporized rock formed a global plume that condensed and deposited this material as spherule bed deposits. These deposits are still preserved in South Africa and Australia today. Unfortunately, the early Earth's exposed rock record is limited to small regions and is largely comprised of crustal rocks that are dissimilar to modern crustal rocks, most importantly in lacking any clear indication of oceanic crust forming at spreading centers, or of continental crust creating stable platforms. Thus, studies of the early Earth are commonly limited to models and proxies to determine the early crust formation, timing of initiation of plate tectonics, and continental crust extraction. This CAREER research project will investigate the geochemistry of the preserved meteor impact deposits to determine crustal and mantle composition at the impact sites, and identify plume processes in the atmosphere associated with impact. Many of the concepts intrinsic to the research are spaciotemporal, such as deep time and penetrative thinking. Because STEM performance is highly linked to spatial skills, in parallel with the geological research program, the pedagogic component of this research focuses on developing tools to improve 3D thinking in undergraduate and graduate students, and testing the tools to determine the efficacy in learning.The overarching scientific questions that guide the geological component of this research are: (1) What is the ocean crust and upper mantle composition at the site of numerous large impacts from 3.5 to 2.4 billion years ago and what can that tell us about the Precambrian crust? (2) How do impact plumes form, condense, and crystallize and what effect do the plumes have on the atmosphere? This CAREER project will address these questions through an integrated program of fieldwork in the Pilbara craton of Australia and the Kapvaal craton of South Africa, modeling, petrography, micro-computed tomography, scanning electron microscopy, and other geochemical analyses to characterize the ocean/mantle target rock and impactites. This research will provide a unique insight into the composition of otherwise unpreserved Precambrian ocean crust and mantle, and will constrain the geochemical and mechanical processes that occur in impact plumes, to improve our understanding of the impact process as a whole and the environmental effects of these impacts. The pedagogic component of the research plan focuses on the communication of large-scale 3D concepts that are a struggle for students, and helps students move from 2D information typical of a classroom to 3D understanding. Because communicating complex spatial concepts is difficult with language alone, this project studies the effect of gesture in large classrooms, which is a particularly useful tool for early undergraduate learners. In addition, this research investigates the use of 3D printing technology to improve 3D visualization and promote universal design for learning.

两个地质过程从根本上塑造了地球的早期历史：大规模、频繁的流星撞击、地壳物质的形成和板块构造的启动。对早期地球的更大、更频繁的影响将对大气、海洋和地球表面产生重大影响。其中许多撞击蒸发了世界范围内几米深的海水，挖掘并蒸发了深达上地幔的岩石，并且发生的频率确保了它们影响了生命的早期进化。 3500至24亿年前的10多次大型撞击将地壳的不同部分挖掘到上地幔中，蒸发的岩石形成了全球羽流，将这种物质凝结并沉积为球粒床沉积物。 这些矿藏至今仍保存在南非和澳大利亚。不幸的是，早期地球暴露的岩石记录仅限于小区域，并且主要由与现代地壳岩石不同的地壳岩石组成，最重要的是缺乏任何明确的迹象表明海洋地壳在扩张中心形成，或大陆地壳形成稳定的平台。因此，早期地球的研究通常仅限于确定早期地壳形成、板块构造起始时间和大陆地壳提取的模型和代理。该职业研究项目将调查保存下来的流星撞击沉积物的地球化学，以确定撞击地点的地壳和地幔成分，并确定与撞击相关的大气中的羽流过程。该研究固有的许多概念都是时空的，例如深度时间和穿透性思维。由于 STEM 表现与空间技能高度相关，因此与地质研究项目并行，本研究的教学部分侧重于开发工具来提高本科生和研究生的 3D 思维，并测试这些工具以确定学习效果。指导本研究地质部分的首要科学问题是：(1) 3.5 至 24 亿年多次大撞击地点的洋壳和上地幔成分是什么 几年前，这能告诉我们关于前寒武纪地壳的什么信息？ (2) 撞击羽流是如何形成、凝结和结晶的？这些羽流对大气有什么影响？该职业项目将通过澳大利亚皮尔巴拉克拉通和南非卡普瓦尔克拉通的实地考察综合计划、建模、岩相学、微型计算机断层扫描、扫描电子显微镜和其他地球化学分析来解决这些问题，以表征海洋/地幔目标岩石和冲击岩。这项研究将对未受保护的前寒武纪海洋地壳和地幔的组成提供独特的见解，并将限制撞击羽流中发生的地球化学和机械过程，以提高我们对整个撞击过程以及这些撞击对环境影响的理解。该研究计划的教学部分侧重于对学生来说很困难的大规模 3D 概念的交流，并帮助学生从课堂上典型的 2D 信息转向 3D 理解。由于仅靠语言很难传达复杂的空间概念，因此该项目研究了大教室中手势的效果，这对于早期本科学习者来说是一个特别有用的工具。此外，本研究还探讨了使用 3D 打印技术来改进 3D 可视化并促进通用学习设计。