Early Proterozoic Crustal Evolution: Geochemical and Neodymium Isotopic Evidence from Sedimentary Rocks

早元古代地壳演化：来自沉积岩的地球化学和钕同位素证据

• 批准号: 8816386
• 负责人: Scott McLennan
• 金额: $ 7万
• 依托单位: SUNY at Stony Brook
• 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: 1989-01-01 至 1991-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8816386&HistoricalAwards=false
• 关键词: Early; Proterozoic; Crustal; Evolution; Geochemical

A powerful approach to the investigation of terrigenous sedimentary rocks is through combined study of petrography, major and trace element geochemistry, mineral chemistry and Nd- isotopic study. Such data provide critical evidence regarding the composition and mean age of he provenance. Using this approach, important constraints are provided for models of crustal composition, growth and evolution. Questions of tectonic setting and recycling history of sedimentary rocks can also be addressed. Isotopic evidence indicates that an important period of crustal growth occurred during the early Proterozic of North America at about 1.9-1.7 Ga. Evidence from Australia and Europe suggests this episode of crustal growth may have been of global significance. It is here proposed to examine the petrographical, geochemical and Nd-isotopic composition of two sedimentary sequences which were deposited at about this time, including the Chelmsford Formation (ca. 1.85 Ga) of the Sudbury region, Ontario and the Vadito - Ortega Groups (ca. 1.7 Ga) of northern New Mexico. The Chelmsford Formation is a proximal turbidite unit deposited in response to early development of the Penokean Orogeny. The Vadito - Ortega Groups are representative of sedimentary rocks deposited during crustal growth in southwestern U.S.A. at about 1.9 - 1.7 Ga. From this study, it will be possible to place important constraints on the nature of crustal growth and evolution during the early Proterozoic. Comparisons with crust-forming events at other times in earth history (particularly at the Archean - Proterozoic boundary) will help to test current models of crustal evolution.

岩石学、常量元素和微量元素地球化学、矿物化学和Nd同位素研究相结合，是陆源沉积岩研究的有力途径。这些数据为种源的组成和平均年龄提供了关键证据。利用这一方法，为地壳成分、生长和演化模型提供了重要的约束。构造背景和沉积岩再循环史的问题也可以解决。同位素证据表明，北美早元古代有一个重要的地壳增长期，约为1.9~1.7Ga。来自澳大利亚和欧洲的证据表明，这一时期的地壳增长可能具有全球意义。本文研究了大约在这个时期沉积的两个沉积序列的岩石学、地球化学和Nd同位素组成，包括安大略省萨德伯里地区的切姆斯福德组(约1.85Ga)和新墨西哥州北部的Vadito-Ortega群(约1.7Ga)。切姆斯福德组是为响应佩诺基期造山运动的早期发展而沉积的近端浊积岩单元。Vadito-Ortega群是美国西南部地壳生长期间沉积的具有代表性的沉积岩，年龄约为1.9-1.7Ga。通过这项研究，将有可能对早元古代地壳生长和演化的性质施加重要的限制。与地球历史上其他时期(特别是太古代-元古界)的地壳形成事件进行比较，将有助于检验目前的地壳演化模型。