Collaborative Research: Precambrian Crustal Evolution in Western Laurentia: Implications from the Sawtooth Metamorphic Complex

合作研究：西劳伦西亚前寒武纪地壳演化：锯齿变质杂岩的影响

• 批准号: 1145212
• 负责人: Paul Mueller
• 金额: $ 27.02万
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-05-01 至 2017-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1145212&HistoricalAwards=false
• 关键词: Collaborative; Research; Precambrian; Crustal; Evolution

Earth scientists from Louisiana State University and the University of Florida are collaborating on an investigation of a unique segment of Precambrian (550 million years old, m.y.o.) continental crust brought to the earth?s surface by the ~50 m.y.o. Sawtooth batholith in eastern Idaho. This crust is unique because it lies between some of the oldest crust in North America (exposed in SW Montana) and some of the most recent additions to the North American continent in western Idaho (Blue Mountains). This research will test a wide range of hypotheses for the formation and evolution of this crust: Is it an independent terrane accreted to North America in the recent past, or does it show geochemical ties to the old (3000 m.y.o.) crust exposed in SW Montana? Does it record evidence of a ?vanished? episode of mountain building similar in age to the Grenville orogeny that formed much of eastern North America 1000 m.y. ago? If accreted to North America in the Precambrian, does it provide insight the fragmentation of North America that occurred 500-700 m.y.o ago? Specifically, the team will investigate the origin of metamorphosed sedimentary rocks that carry information about the nature of continental crust exposed at the time they were deposited. The temperature and pressure history of this crust, which will constrain the time at which it was appended to North America and the mechanism by which it was appended. Elemental abundances in the metamorphosed igneous rocks will give important clues to the environment in which they formed, while isotopic compositions will constrain the amount of new crust vs. recycled crust that is preserved. A large fraction of the crust that lies between the Archean (2500 m.y.o.) crust of SW Montana and the 200 m.y.o. crust of western Idaho is buried beneath younger rocks, making the Sawtooth terrane a very important window into crustal evolution in western North America. This research will be carried out by a team that includes members from underrepresented groups and women who will be trained in important quantitative techniques applicable across a range of STEM disciplines. The team will also participate in the public-private partnership between LSU Geology & Geophysics and Marathon Petroleum Corporation (Geoscience Diversity Enrichment Program) that is focused on increasing STEM participation. The public will also benefit by our partnership with the Sawtooth National Recreational Area (U.S. Forest Service), leading to better educational materials distributed in the Sawtooth National Recreational Area. In detail, this team (faculty and students, undergraduate and graduate) will employ and provide training in the following: 1) We will conduct U/Pb radiometric dating of zircons to determine original crystallization ages of igneous rocks and the origin of sediment deposited in protoliths to the metasedimentary rocks using laser ablation to sample individual crystals in the ICP-MS laboratory at the University of Florida; 2) Elemental analyses by a combination of x-ray fluorescence and ICP methods at the University of Florida; 3) The electron microprobe laboratory at LSU will be used to measure elemental abundances in individual minerals, which can then be used to determine the burial conditions and pressure-temperature path of the Sawtooth crust (thermobarometry); 4) U-Th-Pb (radiometric) dating of texturally and petrologically constrained monazite and titanite will provide a definitive age for the metamorphic event(s) recorded in the Sawtooth crust needed to develop Pressure-Temperature-time path(s) and determine the tectonic setting of metamorphism using facilities at the University of Florida and the University of Massachusetts; and 5) Measurement of K-Ar systematics (40Ar/39Ar) will help assess the most recent, post-metamorphic, thermal history of the terrain. Students from both universities will cross-train in these techniques as part of their thesis and dissertation research, and will then be well prepared to meet the technologically challenging opportunities afforded members of the country?s STEM workforce.

来自路易斯安那州立大学和佛罗里达大学的地球科学家正在合作调查前寒武纪（距今 5.5 亿年）大陆地壳的独特部分，该部分是由约 50 米的地球带到地球表面的。爱达荷州东部的锯齿岩基。这种地壳是独一无二的，因为它位于北美一些最古老的地壳（暴露在蒙大拿州西南部）和爱达荷州西部北美大陆的一些最新地壳（蓝山）之间。这项研究将测试有关该地壳形成和演化的各种假设：它是近代北美增生的独立地体，还是与蒙大拿州西南部暴露的古老（3000 m.y.o.）地壳有地球化学联系？它是否记录了“消失”的证据？与格伦维尔造山运动年龄相似的造山事件，格伦维尔造山运动形成了北美东部的大部分地区，距今1000米前？ 如果它是在前寒武纪时期沉积到北美的，它是否可以让我们了解 500-700 年前发生的北美分裂？ 具体来说，该团队将调查变质沉积岩的起源，这些沉积岩携带着沉积时暴露的大陆地壳性质的信息。 该地壳的温度和压力历史，将制约其附着到北美的时间和附着机制。 变质火成岩中的元素丰度将为它们形成的环境提供重要线索，而同位素组成将限制新地壳与所保存的再生地壳的数量。 地壳的很大一部分位于蒙大拿州西南部的太古代（2500 m.y.o.）地壳和 200 m.y.o. 地壳之间。爱达荷州西部的地壳埋藏在较年轻的岩石之下，使锯齿地体成为了解北美西部地壳演化的一个非常重要的窗口。 这项研究将由一个团队进行，其中包括来自代表性不足群体的成员和女性，他们将接受适用于一系列 STEM 学科的重要定量技术的培训。 该团队还将参与路易斯安那州立大学地质与地球物理学与马拉松石油公司之间的公私合作伙伴关系（地球科学多样性丰富计划），该计划的重点是增加 STEM 参与。公众还将受益于我们与锯齿国家休闲区（美国林务局）的合作，从而在锯齿国家休闲区分发更好的教育材料。 具体而言，该团队（教师和学生、本科生和研究生）将聘用并提供以下方面的培训： 1）我们将进行锆石 U/Pb 放射性测年，以确定火成岩的原始结晶年龄和沉积物的来源。在佛罗里达大学的 ICP-MS 实验室中，使用激光烧蚀对单个晶体进行采样，将原岩转化为变沉积岩； 2）佛罗里达大学结合X射线荧光和ICP方法进行元素分析； 3）路易斯安那州立大学的电子探针实验室将用于测量单个矿物中的元素丰度，然后可用于确定锯齿地壳的埋藏条件和压力-温度路径（温压测量）； 4) 对结构和岩石学约束的独居石和钛矿进行 U-Th-Pb（放射性）测年，将为锯齿状地壳中记录的变质事件提供确定的年龄，以开发压力-温度-时间路径并确定利用佛罗里达大学和马萨诸塞大学的设施研究变质作用的构造环境； 5) K-Ar 系统学 (40Ar/39Ar) 测量将有助于评估该地形最近的变质后热历史。 作为论文和论文研究的一部分，两所大学的学生将进行这些技术的交叉培训，然后做好充分准备，迎接该国 STEM 劳动力成员面临的技术挑战。