Early Archean Crust-Mantle Development: Isotopic and Geochemical Constraints from the North Atlantic Craton

需要资金支持拉布拉多北部Saglek-Hebron地区早期太古代片麻岩杂岩演化的合作研究。该研究区域是北大西洋克拉通的一部分，北大西洋克拉通是太古宙的一个主要地块，保存着3800 Ma前地壳形成的零星证据。研究的目标是：通过记录3800 Ma前地壳的例子来记录北大西洋克拉通；从包含非常古老的地壳的地体开始的区域；以及地壳演化模型。将对以下方面进行研究：(1)英云闪长岩和奥长英质片麻岩和前Uivak片麻岩；(2)各种超镁铁质岩性，其中一些岩性在3600 Ma之前的Uivak片麻岩中以构造侵位的形式出现。乌瓦克和前乌瓦克英云闪长质片麻岩的岩石成因信息将从主元素和微量元素地球化学中获得。年龄数据将通过分析Sm-ND、Rb-Sr和Pb-Pb同位素体系和应用Kober(1986)单颗锆石TIMS技术来获得。这将提供更多的岩石成因数据，并将能够确定地幔分离年龄、源区成分和岩套的变质历史。早期太古代超镁铁质单元的组成、年龄和地壳驻留史的信息将通过全岩和分离矿物相的地球化学和Sm-ND、Pb-Pb和Rb-Sr同位素研究而获得。将在加州大学洛杉矶分校进行同位素地球化学研究。俄克拉荷马大学的韦弗将进行常量和痕量元素(包括稀土)的地球化学研究。这项研究将直接制约北大西洋克拉通太古宙早期地壳的年代学和化学演化。这些限制对于地球早期分馏的模型将是重要的。

Funds are requested to support collaborative research on the evolution of the early Archean gneiss complex in the Saglek- Hebron area, northern Labrador. The study area forms part of the North Atlantic Craton, a major Archean block that preserves fragmentary evidence of pre-3800 Ma crust formation. Objectives of the study are to: North Atlantic Craton by documenting examples of pre-3800 Ma crust; regions from a terrane that contains extremely ancient crust; and to crustal evolutionary models. Research will carried out on: (1) tonalitic and trondhjemitic Uivak and pre-Uivak gneisses; and (2) a variety of ultramafic lithologies, some of which occur as tectonically emplaced rafts within pre-3600 Ma Uivak gneisses. Petrogenetic information for Uivak and pre-Uivak tonalitic gneisses will be obtained from major and trace element geochemistry. Age data will be derived through analysis of Sm-Nd, Rb-Sr, and Pb-Pb isotopic systems and by application of the Kober (1986) single zircon TIMS technique. This will provide additional petrogenetic data, and will enable mantle separation ages, source compositions and metamorphic histories of the suites to be determined. Information on the composition, age and crustal residence history of early Archean ultramafic units will be achieved by a geochemical and Sm-Nd, Pb-Pb and Rb-Sr isotopic study of whole rocks and separated mineral phases. Isotope geochemistry will be carried out at UCSC. Major and trace element (including REE) geochemistry will be carried out by Weaver at the University of Oklahoma. The study will provide direct constraints on the chronology and chemical evolution of early Archean crust in the North Atlantic Craton. These constraints will be important for models of the early fractionation of the Earth.