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.

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研究一部分前寒武纪（5.5亿年历史，M.Y.O。）大陆壳由〜50 M.Y.O.带到地球上的大陆地壳。爱达荷州东部的锯齿浴石。这种外壳是独一无二的，因为它位于北美最古老的地壳之间（在SW蒙大拿州暴露于）和爱达荷州西部北美大陆（蓝山）的一些最近增加。这项研究将检验该地壳形成和演变的广泛假设：最近过去是北美的独立地形，还是在SW Montana中暴露于旧的（3000 M.Y.O.）地壳的地球化学关系？它记录了消失的证据吗？山区建筑的发作与格伦维尔的造口相似，北美东部大部分地区1000 M.Y.前？ 如果在前寒武纪被吸收到北美，它是否提供了发生在500-700 m.y.o之前的北美分裂？ 具体而言，该小组将研究变态岩石的起源，这些岩石含有有关在沉积时暴露于大陆壳的性质的信息。 这种地壳的温度和压力历史将限制将其附加到北美的时间以及附加的机制。 变形的火成岩中的元素丰度将为它们形成的环境提供重要的线索，而同位素组合物将限制保留的新外壳与再生地壳的数量。 SW Montana的Archean（2500 M.Y.O.）外壳和200 M.Y.O.爱达荷州西部的外壳被埋在年轻的岩石下，使锯齿状的地形成为北美西部地壳进化的非常重要的窗口。 这项研究将由一个团队进行，其中包括来自代表性不足的团体和女性的成员，这些成员将接受适用于一系列STEM学科的重要定量技术培训。 该团队还将参加LSU地质与地球物理学与马拉松石油公司（地球科学多样性丰富计划）之间的公私合作伙伴关系，该合作旨在增加STEM参与。公众还将通过我们与锯齿国家娱乐区（美国森林服务局）的合作伙伴关系而受益，从而导致在锯齿齿全国娱乐区分发的更好的教育材料。 详细介绍，该团队（教职员工，本科生和毕业生）将在以下内容中采用并提供培训：1）我们将进行锆石的U/PB辐射仪，以确定点火岩石的原始结晶年龄，以及沉积物的起源以及在Protolith中沉积在Protoliths中的沉积物的起源2）通过在佛罗里达大学的X射线荧光和ICP方法的组合进行元素分析； 3）LSU的电子微探针实验室将用于测量各个矿物质的元素丰度，然后可以用来确定锯齿状外壳的埋葬条件和压力温度路径（热计量法）； 4）在质地和岩石学约束的独居石和钛铁矿上的U-TH-PB（辐射时间计）将为在锯齿状的地壳中记录的变态事件（S）提供确定的年龄，以开发压力温度的时间路径（S），并确定使用佛罗里达大学和大学属于佛罗里达大学的变质设施的构造设施的构造设置， 5）测量K-AR Systematics（40AR/39AR）将有助于评估地形后最新的，后型后的热史。 来自两所大学的学生将作为论文和论文研究的一部分进行交叉培训，然后将做好充分的准备，以实现在技术上具有挑战性的机遇，为国家的STEM劳动力提供了挑战。