Collaborative Research: Creating Earth’s earliest continents—an integrated investigation of the growth and modification of western Australia’s Pilbara Craton

地球最早期大陆的形成是地球科学中的一个重要课题。一个主要的问题是，从地球最早的历史中保存下来的岩石是罕见的;地球历史的第一个十亿年的岩石很少，从第一个5亿年开始就没有完整的岩石。 地质学家必须使用非常零碎的记录来确定第一个大陆地壳是何时形成的，它的成分是什么，以及它存在的程度。 这笔赠款将支持地质学家研究地球上最古老的、未经修改的构造板块碎片--西澳大利亚的皮尔巴拉板块--以解决这些问题。 方法是首先通过充当放射性时钟（地质年代学）的矿物（例如锆石）的形成来确定岩石的年龄。一旦知道了年龄，岩石的化学成分就可以确定它们是来自更早的地壳还是直接从地幔中提取出来的（地球化学）。 这些岩石的模式和结构（构造地质学），当与地球化学和地质年代学相结合时，将决定岩石是如何以及何时加入地壳以创造这些早期大陆的。 这项工作的主要成果将是更好地了解地球最早期地壳的历史及其形成过程，这项工作包括学生培训、指导和支持一名初级科学家（博士后研究员）以及国际合作。 此外，与认知科学家一起工作将帮助学生在大的时间尺度上想象地质过程。 该提案将允许国内和国际访问者在WSU同位素实验室开发复杂的地球化学和地质年代学分析技术，并使用它们。该提案旨在通过检查西澳大利亚州3.5 - 2.8 Ga东皮尔巴拉山的花岗岩杂岩--埃德加山和科鲁纳山--和相关的表壳岩，通过综合地质年代学、地球化学和构造研究。 东皮尔巴拉火山岩是地球上保存最完好的古-中太古代地壳之一，展示了经典的圆顶和龙骨模式，其中花岗岩复合体（圆顶）被陡峭倾斜的火山岩和火山岩表壳岩石地层（龙骨）包围。 两个中心的，相互关联的问题指导我们的研究：1）花岗岩复合体的侵位机制和时间是什么; 2）东皮尔巴拉岩石的地幔和地壳源区是什么。 为探讨这些问题，我们的工作重点是：1）成分和变形不均匀的花岗质穹隆杂岩的地球化学和结构; 2）地壳岩石地层变形区的时代、变质条件和结构（“绿石龙骨”）;地壳岩石地层和花岗质穹隆中变形最小区域的变质火山岩的地球化学特征，以解决地幔和地壳源区的问题。 这种综合的地球化学和结构方法将提供有关一级构造过程的信息，这些过程导致地球上最早的地壳之一的形成，修改和稳定，因此，为地球上最早的大陆地壳的形成和保存提供重要的见解。该项目得到岩石学&地球化学和构造计划的支持。该奖项反映了NSF的法定基金会的使命是履行其使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评价，被认为值得支持。

The formation of Earth’s earliest continents is topic of significant interest in the Earth Sciences. A major issue is that rocks preserved from Earth’s earliest history are rare; there are few rocks from the first billion years of Earth’s history, and no intact rocks at all remaining from the first 500 million years. Geologists must use a very fragmental record to determine when first continental crust formed, what was it composition, and how much of it existed. This grant will support geologists to study the Earth’s oldest, unmodified fragment of a tectonic plate – the Pilbara terrane of West Australia – to address these issues. The approach is to first determine the age of the rocks through the formation of minerals, such as zircons, that act a radioactive clocks (geochronology). Once the age is known, the chemistry of the rocks can determine if they were derived from an earlier crust or extracted directly from the Earth’s mantle (geochemistry). The patterns and fabrics of these rocks (structural geology), when integrated with geochemistry and geochronology, will determine how and when the rocks were added to the crust to create these early continents. The major outcome of this work will be a better understanding of the history of the Earth’s earliest crust and the processes that formed it. The work includes student training, mentorship and support for a junior scientist (post-doctoral fellow), and international collaboration. Additionally, work with a cognitive scientist will help students envision geological processes over large time scales. The proposal will allow technique development of sophisticated geochemical and geochronologic analyses and their use in the WSU isotope laboratory by national and international visitors.This proposal seeks to address the fundamental processes of crustal formation, modification, and stabilization by examining granitic complexes—the Mt Edgar and Corunna Downs—and associated surpracrustal rocks of the 3.5 – 2.8 Ga East Pilbara terrane of West Australia, through an integrated geochronological, geochemical, and structural study. The East Pilbara terrane is one of the best-preserved examples of Paleo- to Mesoarchean crust on Earth, displaying the classic dome-and-keel pattern in which granitic complexes (domes) are surrounded by steeply dipping volcanic and volcaniclastic supracrustal lithostratigraphy (keels). Two central, interlinking questions guide our research: 1) What were the mechanisms and timing of emplacement of the granitic complexes; and 2) What were the mantle and crustal source regions for the rocks of the East Pilbara terrane. To investigate these questions, our work will focus on: 1) The geochemistry and structure of the compositionally and deformationally heterogeneous granitic dome complexes; 2) The timing, metamorphic conditions, and structure in the deformed regions of the supracrustal lithostratigraphy (“greenstone keels”); and 3) The geochemistry of the metavolcanic rocks in the supracrustal lithostratigraphy and the grantic domes, in regions of minimal deformation, to address the mantle and crustal source regions. This integrated geochemical and structural approach will provide information on first-order tectonic processes that resulted in the formation, modification, and stabilization of one of Earth’s earliest cratons and, therefore, provide important insights into the formation and preservation on some of the earliest continental crust on Earth.This project is supported by both the Petrology & Geochemistry and Tectonics programs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.