A Nd Isotopic Study of Early Proterozoic Crustal Growth in Southern Wyoming

怀俄明州南部早元古代地壳生长的 Nd 同位素研究

• 批准号: 8904806
• 负责人: Lang Farmer
• 金额: $ 5万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1989
• 资助国家: 美国
• 起止时间: 1989-07-15 至 1991-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8904806&HistoricalAwards=false
• 关键词: Nd; Isotopic; Study; Early; Proterozoic

Sm-Nd isotope systematics will be applied to Precambrian metasedimentary and metaigneous rocks in and adjacent to the Cheyenne Belt (CB), an ancient crustal suture zone in southern Wyoming, constrain models for the genesis of Proterozoic continental crust and for the accretion of these crustal segments to the margins of preexisting Archean continental cratons. The Cheyenne Belt represents a rare example of a well exposed Archean continental margin in North America which is apparently not directly mantled by a large segment of "mixed" Proterozoic crust, that is, crust produced in the Proterozoic that intermixed with Archean crustal material. The proposal will center on determining whether the lack of such crust at the southern margin of the Wyoming craton reflects the fact that such crust was never accreted in this region (unlike other segments of Archean cratonal margins) or whether tectonic movement along the CB has removed and mixed crust that may have originally been present. Three separate, but interrelated projects will be undertaken 1) Sm-Nd isotope systematics of Proterozoic miogeoclinal sedimentary rocks north of the CB. The purpose will be to use the temporal variations in the Nd isotopic compositions of these sediments to determine whether Proterozoic island arcs composed of newly formed juvenile or "mixed" crustal material initially approached the ancient continental margin, 2) Sm-Nd isotopic systematics of para-and orthogneisses in tectonic blocks within the CB itself, to determine if these rocks represents remnants of "mixed crust that might have initially accreted against the southern margin of the Wyoming craton, and 3) the isotope systematics of Proterozoic igneous and metasedimentary rocks of the Colorado province south of the CB, to determine if "mixed" crust is present in the northernmost portions of this terrane, and to determine if the metasedimentary rocks record the isotopic characteristics (Archean or "mixed" crust) of the crust against which this terrane initially impinged. The results of all three projects will be integrated with existing geologic and tectonic data in an attempt to construct a model for the Precambrian tectonic evolution of the southern margin of the Wyoming Archean craton.

Sm-Nd同位素系统学将在前寒武纪应用 变质沉积岩和变质火成岩 夏延带（CB）是中国南方的一条古地壳缝合带 怀俄明州，元古宙成因的约束模型 大陆地壳和这些地壳段的增生 到先存的太古代大陆边缘 的 夏延带是一个罕见的太古宙暴露良好的例子 北美大陆边缘， 直接被一大块“混合”的元古代地壳覆盖， 也就是说，在元古代产生的地壳， 太古代地壳物质。 该提案将集中在 确定南部边缘是否缺乏这种地壳 怀俄明州克拉通的地壳反映了这样一个事实， 在这一地区增生（不同于太古代的其他部分 或构造运动是否沿着CB 去除并混合可能最初存在的外壳。 将开展三个独立但相互关联的项目1） 元古宙微斜地沉积Sm-Nd同位素体系 CB以北的岩石 目的是利用时间 这些沉积物的Nd同位素组成的变化， 确定元古代岛弧是否由新的 形成的幼年或“混合”地壳物质最初接近 古大陆边缘Sm-Nd同位素体系 CB内部构造块体中的准片麻岩和正片麻岩， 以确定这些岩石是否代表“混合地壳”的残余 最初可能是在南极洲的南部边缘 怀俄明州克拉通; 3）元古代同位素系统 产于科罗拉多省南部的一种火成岩和变质沉积岩 的CB，以确定是否“混合”地壳存在于 这是最大的部分，并确定是否 变质沉积岩记录了同位素特征 （太古代或“混合”地壳）的地壳， 一开始是撞击。 三个项目的成果 将与现有的地质和构造数据相结合， 试图建立一个前寒武纪构造模式 怀俄明州太古代克拉通南缘的演化。