International Geologiical Congress - Oslo 2008


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GDP-04 Palaeozoic-Mesozoic earth geography: Palaeomagnetic, faunal and facies constraints


Dynamic Plate boundaries: A method of reconstructing the past


Cyril Hochard, Université de Lausanne (Switzerland)
Gérard Stampfli, Université de Lausanne (Switzerland)


Plate tectonics is the process which governs the evolution of geodynamic environments across the Earth's surface. Reconstructing the past requires to reconstruct the plates. Paleomagnetic, faunal and facies constraints lead to retrieve the past distribution of continents. They offer the ideal framework for reconstructing plates including oceanic realms. Starting from those data, we present an interdisciplinary approach including all at once Geology, Paleomagntism and Paleogeography (Paleobiogeography and Paleoclimatology) and aiming to retrace the evolution of plate boundaries through times.
In this approach inter-dependant reconstructions are created from the past to the present. Except during collisions, plates are moved step by step, as single rigid entities. The only evolving elements are the plate boundaries which are preserved and follow a consistent geodynamical evolution through time and an interconnected network through space. Hence, lithospheric plates are constructed by adding/removing oceanic material (symbolized by synthetic isochrones) to major continents and terranes. Through time, five "key assemblies" of continents have been created mainly using Paleomagnetic and Paleogeographic data. In between those key assemblies, geodynamic scenarios are imagined to move plates from one to the next. All along the process, plate motions are controlled by geological/geodynamic and kinematic constraints. When discrepancies occur, either the key assemblies or the geodynamic scenarios have to be revised. The process is thus fully iterative.
In the last years we changed our tools and moved into GIS softwares to build a geodynamic database supporting the reconstructions. Automation of reconstruction and verification tasks helped us to develop a set of 41 reconstructions ranging from the late Neo-proterozoic (600Ma) to the present with an average step of ca. 15 Ma. Those reconstructions include a new set of 340 Terranes properly defined. Using the possibilities offered by GIS we also developed new kind of models such as velocity models and paleobathymetric models bringing new constraints and thus increasing the robustness of the model.


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