Deep seismic imaging the evolution of continental lithosphere

随着地球变冷，地球的构造过程发生了巨大的变化。45亿年前地球形成后不久，它的表面就形成了一层厚厚的不动的基性地壳，以广泛的火山活动为标志，也许偶尔会发生重大的地表重塑事件，因为火山柱在混乱的地幔对流状态下向上输送热量。大约30 - 35亿年前，一种雏形的短暂板块构造发展起来，最终演变成我们今天所看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，但是这些早期构造过程的性质仍然存在争议，密集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。我们对早期地球的认识来自于各种各样的地球科学数据和日益复杂的数值地球动力学模拟，这些数据可以预测各种情况下地壳和上地幔的变形。由于深地震反射测量可以揭示大陆岩石圈中早期构造变形时期保存的详细结构，因此这些测量为验证地球动力学建模的预测提供了一种理想的方法，并且它们的深度限制是对地表地质测绘的重要补充。最近在澳大利亚记录的高质量地震数据建立在加拿大Lithoprobe项目大量数据集的基础上，为了解古代大陆地壳结构提供了前所未有的见解。这项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第一个微大陆的形成到今天大陆稳定核心的组装的变化构造过程的本质。利用新开发的方法，在弯曲的二维勘探中确定三维反射器的方向，现在可以更好地区分多个构造变形阶段。我将与我的学生一起研究太古宙地壳的聚集和随后的崩塌，这可能没有现代的等价物，确定下地壳流动的性质，并揭示太古宙绿岩带的背景，这些绿岩带拥有地球上大部分的黄金和贱金属资源。地震调查表明，在早元古代或之前，大陆组合的性质发生了重大变化，地壳剖面非常厚，这可能与强大的克拉通根的生长有关。我们将开发方法，根据其主要反射方向来区分上地幔中的域，旨在确定它们是由岩浆作用、大陆沉降或俯冲板块叠瓦作用等过程形成的。

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.