REU: Geologic Evolution of the Robertson River Suite: Implications for the Timing, Petrogenesis, and Thermal History of the Late Proterozoic Rifting of Laurentia

REU：罗伯逊河组的地质演化：对劳伦西亚晚元古代裂谷的时间、岩石成因和热史的影响

• 批准号: 8916048
• 负责人: Richard Tollo
• 金额: $ 3.97万
• 依托单位: George Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1990
• 资助国家: 美国
• 起止时间: 1990-02-01 至 1991-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8916048&HistoricalAwards=false
• 关键词: REU; Geologic; Evolution; Robertson; River

The Robertson River Suite (RRS, a.k.a. Robertson River Formation) encompasses a series of metaluminous to peralkaline granitoids and felsites exposed within the core of the Blue Ridge anticlinorium (BRA) in northern and central Virginia. Broad- scale reconnaissance mapping by previous workers has established that the RRS is intrusive into Grenville age (1.0-1.1 G.a.) gneisses and is intruded by numerous greenstone dikes, some of which may have served as feeders to the Catoctin metavolcanics of the BRA cover sequence. The age of the RRS is thus only broadly constrained by field evidence as younger than Grenvillian metamorphism and older than at least most of the late Precambrian Catoctin Formation. Previous attempts using radiometric techniques to determine a more exact timing for emplacement of the suite have produced mutually contradictory data spanning the range 730 to 570 M.a. Much of the reason for these inconsistent data lies in the fact that these studies have either 1) assumed the formation to be homogeneous, and thus accurately characterized by multiple samples collected from throughout the outcrop belt, or 2) acknowledged the apparent heterogeneity of the suite and nevertheless attempted to extrapolate data from one location to the entire body. Neither approach is appropriate, however, in light of new evidence from more detailed field, petrologic, and geochemical studies recently completed in the northern portion of the suite by this research group. These data demonstrate that the RRS encompasses a series of distinct plutons that records an obviously complex petrogenetic history spanning a time interval which may have been considerable. This study proposes to build on this work by 1) completing 1:24,000-scale mapping of the southern portion of the suite, 2) using petrologic and geochemical data to define the nature of the constituent plutons, and 3) obtaining precise and accurate isotopic data bearing on the timing and duration of RRS emplacement. Furthermore, the petrochemical and isotopic data to be obtained in this study will be applied to refine models for the petrogenetic evolution of this compositionally distinctive suite and the isotopic characteristics of probable source regions. In summary, the results of this stud will 1) provide a firm foundation for appropriate petrogenetic models concerning emplacement of this anorogenic suite, 2) place important constraints on the maximum age of prelapetan rifting, 3) establish a database on which to evaluate the relationship of this plutonism to the voluminous felsic lavas included within the Catoctin Formation and felsic intrusives of similar (?) age and composition occurring elsewhere in the central Appalachians, 4) define specific isotopic characteristics of the source areas of magma generation, and 5) lead to the development of geologically reasonable models concerning the petrogenetic evolution of such compositionally unique anorogenic suites.

罗伯逊河畔套房(RRS，又名罗伯逊河组)包括一系列出露在弗吉尼亚州北部和中部蓝岭背斜(BRA)核心内的从铝到过碱性的花岗岩和长石。先前工作人员的大范围勘测已经确定，RRS侵入了格伦维尔年龄(1.0-1.1 G.A.)片麻岩并被许多绿岩岩脉侵入，其中一些可能是文胸盖层序列的Catoctin变火山岩的补给者。因此，RRS的年龄仅受到野外证据的广泛限制，因为它比格勒维利亚变质作用年轻，至少比大多数晚前寒武纪的卡托克廷建造要早。以前使用辐射测量技术来确定套件的更精确定位时间的尝试已经产生了跨越730至570毫安范围的相互矛盾的数据。这些不一致数据的主要原因在于，这些研究要么假设地层是均质的，因此通过从整个露头带收集的多个样本准确地描述地层，要么承认套系的明显不均一性，但仍试图将数据从一个位置外推到整个身体。然而，根据该研究小组最近在该套岩套北部完成的更详细的野外、岩石学和地球化学研究的新证据，这两种方法都是不合适的。这些数据表明，RRS包括一系列不同的深成岩，这些深成岩记录了一段明显复杂的成岩历史，时间跨度可能相当可观。这项研究建议在这项工作的基础上，1)完成1：24,000比例尺的岩套南部测绘，2)使用岩石学和地球化学数据来确定组成深成岩体的性质，以及3)获得与RRS侵位的时间和持续时间有关的精确和准确的同位素数据。此外，这项研究中将获得的岩石化学和同位素数据将用于完善这一成分独特的岩套的岩石成因演化模式和可能源区的同位素特征。总而言之，这项研究的结果将1)为有关该造山带侵位的适当岩石成因模式提供坚实的基础，2)对拉普埃坦前裂谷作用的最大年龄施加重要的限制，3)建立一个数据库，在此基础上评估该深成作用与Catoctin建造中包含的大量长英质熔岩和类似(？)阿巴拉契亚中部其他地方的年龄和成分，4)确定了岩浆生成源区的特定同位素特征，5)导致了关于这种成分独特的非造山岩套的岩石成因演化的地质合理模式的发展。