Deep seismic imaging the evolution of continental lithosphere

随着地球变冷，地球的构造过程发生了戏剧性的变化。在45亿年前形成后不久，地球表面就形成了一个厚厚的静止的镁铁质地壳，以广泛的火山活动为标志，可能不时会有重大的地表重新浮出水面的事件，因为羽流在混乱的地幔对流体系中向上输送热量。大约30-35亿年前，一种萌芽的、瞬时的板块构造形成了，最终演变成了我们今天观察到的组织良好的板块构造系统。地球大陆已经记录了超过40亿年的这种构造活动的影响，但这些早期构造过程的性质仍然存在争议，致密的早期地壳的垂直下沉通常被认为是与海底扩张和俯冲有关的水平过程的替代。我们对早期地球的理解来自于各种各样的地球科学数据和日益完善的地球动力学数值模拟，它们可以预测各种情景下地壳和上地幔的变形。由于深地震反射测量可以详细揭示大陆岩石圈中早期构造变形幕保存下来的结构，这些测量提供了一种验证地球动力学模型预测的理想方式，它们的深度约束是对地表地质制图的关键补充。澳大利亚最近记录的高质量地震数据建立在来自LithoProbe计划的大量加拿大数据集的基础上，并提供了对古代大陆地壳结构的前所未有的洞察。拟议研究的目的是利用地震反射数据，结合广泛的地质和地质年代学数据，确定地球历史早期从创造第一个微大陆到组装今天大陆稳定核心的不断变化的构造过程的性质。使用在弯曲的二维测量中确定三维反射面方向的新方法，现在可以更好地区分多期构造变形。与我的学生一起，我将研究太古宙地壳的组装和随后的崩溃，可能没有现代的类似物，确定下部地壳流动的性质，并揭示太古宙绿岩带的背景，那里蕴藏着地球上大量的黄金和贱金属资源。地震调查表明，大陆组装的性质在早元古代期间或之前发生了重大变化，出现了非常厚的地壳段的俯冲，这可能与强大的克拉通根部的生长有关。我们将开发方法，通过它们的主要反射面方向来区分最上面地幔中的域，目的是确定它们是由岩浆作用、大陆下沉或俯冲板块的叠加作用等过程形成的。

Earth's tectonic processes have changed dramatically as the planet has cooled. Soon after its formation 4.5 billion years ago, Earth's surface comprised a thick immobile mafic crust marked by extensive volcanism, perhaps punctuated by major resurfacing events, as plumes transported heat upward in a chaotic mantle convection regime. Approximately 3.0-3.5 billion years ago, a form of embryonic, transient plate tectonics developed, which eventually evolved into the well organised plate tectonic system we observe today. Earth's continents have recorded the effects of over four billion years of this tectonic activity, but the nature of these early tectonic processes remains controversial with vertical subsidence of the dense early crust often invoked as an alternative to horizontal processes tied to seafloor spreading and subduction. Our understanding of the early Earth comes from a wide variety of geoscientific data and increasingly sophisticated numerical geodynamic simulations, which can predict the deformation of the crust and upper mantle in various scenarios. Since deep seismic reflection surveys can reveal in detail structures preserved in the continental lithosphere from earlier episodes of tectonic deformation, these surveys provide an ideal way to verify the predictions of geodynamic modelling, and their depth constraints are a critical complement to geological mapping at the surface. High quality seismic data recently recorded in Australia build upon extensive Canadian datasets from the Lithoprobe program, and provide an unprecedented insight into the structure of ancient continental crust. The objective of the proposed research is to use seismic reflection data, integrated with a broad range of geological and geochronological data, to determine the nature of the changing tectonic processes that operated early in Earth history from creation of the first microcontinents to assembly of the stable cores of today's continents. Using new methods developed to determine 3-D reflector orientations in crooked 2-D surveys, it is now possible to better distinguish multiple episodes of tectonic deformation. With my students, I will study the assembly and subsequent collapse of Archean crust, which probably has no modern equivalent, determine the nature of lower crustal flow, and reveal the setting of Archean greenstone belts that host much of Earth's gold and base metal resources. Seismic surveys indicate that a significant change in the nature of continental assembly occurred during, or just prior to, the Early Proterozoic, with the underthrusting of very thick crustal sections, which may be related to the growth of strong cratonic roots. We will develop methods to distinguish domains in the uppermost mantle by their dominant reflector orientation, aiming to determine if they formed by processes such as magmatism, continental subsidence, or imbrication of subducted slabs.