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

点击翻译按钮获取中文摘要

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.