Deep seismic imaging the evolution of continental lithosphere

深地震成像大陆岩石圈的演化

• 批准号: RGPIN-2018-04185
• 负责人: Calvert, Andrew
• 金额: $ 2.62万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=686570
• 关键词: Deep; seismic; imaging; evolution; continental

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.

随着地球的冷却，地球的构造过程发生了巨大的变化。在45亿年前形成后不久，地球表面就形成了一个厚厚的不动的镁铁质地壳，其特征是广泛的火山活动，也许会被重大的表面重塑事件所打断，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，一种胚胎形式的短暂板块构造发展起来，最终演变成我们今天观察到的组织良好的板块构造系统。地球各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，致密早期地壳的垂直沉降通常被认为是与海底扩张和俯冲有关的水平过程的替代方案。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。由于深地震反射勘测可以详细揭示大陆岩石圈中保存的早期构造变形的结构，这些勘测为验证地球动力学模型的预测提供了一种理想的方法，其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第一个微大陆的形成到今天大陆稳定核心的组合的不断变化的构造过程的性质。使用新的方法来确定弯曲的二维测量中的三维反射体方向，现在可以更好地区分多个构造变形事件。与我的学生，我将研究太古代地壳的组装和随后的崩溃，这可能没有现代的等价物，确定下地壳流动的性质，并揭示了太古代绿岩带的设置，这些绿岩带承载了地球上的大部分黄金和贱金属资源。地震测量表明，大陆组装的性质发生了重大变化，在早元古代期间，或就在此之前，非常厚的地壳部分的下冲，这可能与强大的海底根的生长有关。我们将开发的方法来区分域在上地幔的主导反射体的方向，旨在确定它们是否形成的过程，如岩浆作用，大陆沉降，或俯冲板叠瓦。