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。陆块古经度的计算是古地理学中最具挑战性的问题。由于海底俯冲已经完全抹去了记录200 Ma以前世界运动学的所有海洋磁异常、转换断层和热点轨迹，因此不能用常规方法确定200 Ma以前的古隆起。因此，对侏罗纪以前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经度，而只有当我们能够计算出古代经度时，才能确定陆块的“真实”或绝对位置和古代海洋的实际大小。 我的建议涉及用四种最新的方法进行绝对经度的数值评估，尽管有一些局限性，但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)俯冲板块在地幔中的位置(仅在最后的~250 Ma)，(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，以及大火成岩省和金伯利岩省的地表表达，(4)视极漂移轨迹几何参数化法，该方法能够计算古纬度，但需要可靠的古地磁资料来建立大陆的视极漂移轨迹(仍需为特定年龄和大陆地块建立这样的数据库，特别是在亚洲)。 计算古隆起将使我和我的团队能够建立一个跨度从200 Ma到1000 Ma的完全定量的世界板块构造模型。这种模式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悬而未决的问题：LLSVPS的地幔稳定性假说，与俯冲通量变化对地球发电机的调制和地幔脱气有关的地幔对流周转，洋盆的打开和关闭(威尔逊旋回)，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.