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（5.5亿年历史，m.y.o.）的一个独特部分。大陆地壳被带到了地球上约50百万年前，爱达荷州东部的锯齿状岩基。这个地壳是独一无二的，因为它位于北美最古老的地壳（暴露在蒙大拿州西南部）和爱达荷州西部（蓝山）的北美大陆最近增加的一些地壳之间。这项研究将测试这个地壳的形成和演化的各种假设：它是一个独立的沉积物在最近的过去增生到北美，还是它显示出与旧的地球化学联系（3000百万年）。蒙大拿州西南部的地壳它有没有记录证据？消失了与形成北美东部大部分地区的格伦维尔造山运动相似的造山运动时期。以前？ 如果它在前寒武纪时与北美洲共生，它是否能提供关于5 - 7亿年前北美洲分裂的信息？ 具体而言，该小组将调查变质沉积岩的起源，这些岩石携带有关沉积时暴露的大陆地壳性质的信息。 这个地壳的温度和压力历史，这将限制它被附加到北美的时间和它被附加的机制。 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保存的再循环地壳的数量。 位于太古代（2500百万年）蒙大拿州西南部的地壳和200百万年的地壳。爱达荷州西部的地壳被埋在较年轻的岩石之下，这使得锯齿岩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的群体和妇女的成员，他们将接受适用于一系列STEM学科的重要定量技术的培训。 该团队还将参加路易斯安那州立大学地质地球物理学和马拉松石油公司（地球科学多样性丰富计划）之间的公私合作伙伴关系，该计划的重点是增加STEM的参与。公众也将受益于我们与锯齿国家休闲区（美国林务局）的合作伙伴关系，从而在锯齿国家休闲区分发更好的教育材料。 具体来说，这个团队（教师和学生，本科生和研究生）将雇用和提供以下培训：1）我们将进行锆石的U/Pb放射性测年，以确定火成岩的原始结晶年龄和沉积在原岩中的沉积物的起源，以变质沉积岩，使用激光烧蚀在佛罗里达大学的ICP-MS实验室采样单个晶体; 2）在佛罗里达大学采用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显微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壳的埋藏条件和压力-温度路径（热压法）; 4）U-Th-Pb对结构和岩石学约束的独居石和钛铁矿进行（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，以确定压力-温度-时间路径并利用佛罗里达大学和马萨诸塞州大学的设备确定变质作用的构造背景; 5）K-Ar系统（~（40）Ar/~（39）Ar）的测定将有助于评价该区变质后的热历史。 来自这两所大学的学生将交叉培训这些技术作为他们的论文和论文研究的一部分，然后将做好充分准备，以满足技术上具有挑战性的机会提供给国家的成员？STEM劳动力。