Absolute reconstructions of continents for one billion years: developing new quantitative approaches

十亿年来大陆的绝对重建：开发新的定量方法

• 批准号: RGPIN-2019-04780
• 负责人: Kravchinsky, Vadim
• 金额: $ 2.62万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=762510
• 关键词: Absolute; reconstructions; continents; billion; years

Our understanding of Earth's plate kinematics and dynamics has evolved greatly in the last half-century, yet plate tectonic reconstructions prior to ~ 200 Ma remain challenging. The calculation of ancient longitudes of continental blocks is the most challenging problem in paleogeography. Conventional methods to determine paleolongitudes prior 200 Ma cannot be applied because ocean floor subduction has entirely erased all the records of marine magnetic anomalies, transform faults, and hotspot tracks that documented pre-200 Ma world kinematics. The estimated paleolongitude of continents for pre-Jurassic time must then be based on comparisons of fossils or lithofacies. These methods, however, can be used only for determining relative longitudes, whereas "true" or absolute positions of continental blocks and actual sizes of ancient oceans can be determined only when we are able to calculate ancient longitudes. My proposal deals with numerical assessments of absolute longitudes using four recent approaches that, although with some limitations, provide the best longitude evaluations: (1) stationary Africa as a longitudinal anchor, however, only since the Permian, (2) the position of subducted slabs in the mantle (only for the last ~ 250 Ma), (3) the hypothetical position stability of large low shear velocity provinces (LLSVPs) in Paleozoic and Neoproterozoic eras, with surficial expressions in large igneous and kimberlite provinces, (4) apparent polar wander path geometrical parameterization method that enables calculation of paleolongitudes but requires reliable paleomagnetic data to build an apparent polar wander path for a continent (such a database still needs to be built for particular ages and continental blocks, especially in Asia). Calculating paleolongitudes will enable me and my group to build a fully quantitative plate tectonic model of the world spanning from 200 to 1000 Ma. Implementation of such a model will ultimately give us the opportunity to further investigate outstanding questions in contemporary Earth sciences: the hypothesis of mantle stability at LLSVPs, the convective turnover of the mantle, which is related to the modulation of geodynamo and mantle degassing by changes in subduction flux, the opening and closing of ocean basins (the Wilson Cycle), the effect of such geological processes on long-term climate changes and geomagnetic field behavior.

在过去的半个世纪中，我们对地球板块运动学和动力学的理解有了很大的发展，但约 200 Ma 之前的板块构造重建仍然具有挑战性。大陆块古代经度的计算是古地理学中最具挑战性的问题。无法应用确定 200 Ma 之前古经度的传统方法，因为海底俯冲已经完全抹去了记录 200 Ma 之前世界运动学的所有海洋磁异常、转换断层和热点轨迹记录。侏罗纪前时期大陆的估计古经度必须基于化石或岩相的比较。然而，这些方法只能用于确定相对经度，而只有当我们能够计算出古代经度时，才能确定大陆块的“真实”或绝对位置以及古代海洋的实际大小。 我的建议涉及使用四种最近的方法对绝对经度进行数值评估，尽管存在一些局限性，但它们提供了最佳的经度评估：（1）静止的非洲作为纵向锚，然而，仅自二叠纪以来，（2）俯冲的位置地幔中的板片（仅在最后~ 250 Ma），（3）古生代和新元古代大的低剪切速度区（LLSVP）的假设位置稳定性，大型火成岩省和金伯利岩省的地表表现，（4）视极漂移路径几何参数化方法，可以计算古经度，但需要可靠的古地磁数据来建立大陆的视极漂移路径（具体情况仍需要建立这样的数据库）年龄和大陆块，特别是在亚洲）。计算古经度将使我和我的团队能够建立一个跨度从 200 Ma 到 1000 Ma 的完全定量的板块构造模型。这种模型的实施最终将使我们有机会进一步研究当代地球科学中的突出问题：LLSVP 时地幔稳定性的假设，地幔的对流周转，这与地球发电机和地幔脱气的变化的调节有关。俯冲通量、海洋盆地的打开和关闭（威尔逊循环）、此类地质过程对长期气候变化和地磁场行为的影响。