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

在过去的半个世纪里，我们对地球板块运动学和动力学的理解有了很大的发展，但在200 Ma之前的板块构造重建仍然具有挑战性。大陆块体古地温的计算是古地理学中最具挑战性的问题。确定200 Ma前古地磁的传统方法不能应用，因为洋底俯冲已经完全抹去了所有记录海洋磁异常，转换断层和热点轨道，记录了200 Ma前的世界运动学。因此，对前侏罗纪时期大陆的古经度的估计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大陆架，而只有当我们能够计算古代大陆架时，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，尽管有一些限制，但提供了最佳的经度评估：（1）静止的非洲作为纵向锚，然而，只有自二叠纪以来，（2）俯冲板片在地幔中的位置（3）古生代和新元古代大的低剪切速度省（LLSVP）的假设位置稳定性，在大的火成岩省和金伯利岩省中有表层表现;（4）视极移路径几何参数化方法，该方法能够计算古经度，但需要可靠的古地磁数据来建立大陆的视极移路径（对于特定的年龄和大陆块，特别是在亚洲，仍需要建立这样的数据库）。 计算古经度将使我和我的团队能够建立一个完整的定量板块构造模型，涵盖200至1000 Ma的世界。这样一个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：地幔稳定性假说，地幔的对流翻转，这与俯冲通量的变化，海洋盆地的打开和关闭对地球发电机和地幔脱气的调制有关（威尔逊循环），这种地质过程对长期气候变化和地磁场行为的影响。

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.