HR: 09:05h
AN: U31B-05    [Abstracts]
TI: APWPs: Critical Building Steps and Potential for Future Geodynamical Studies.
AU: * besse, j
EM: besse@ipgp.jussieu.fr
AF: ipgp, 4 place jussieu, Paris, 75252 France
AB: Among other items, the Apparent Polar Wander Paths (APWP) of individual tectonic blocks contain information on geodynamical events from both shallower lithospheric sources (e.g. continental breakups and collisions) and deeper mantle sources affected by convection. Recent advances in the Earth Sciences, such as provided by global tomography or climate modeling, have emphasized the essential need for accurate reconstructions of the Earth's surface (blocks, plates and their boundaries and topographies), in order for instance to compare the initial positions of downgoing slabs or emerging hot spots with deeper mantle features, or to understand why and how time-varying climates and biomes may be related. A half century after its initial pionneering contributions to the formulation of continental drift and plate tectonics, paleomagnetism remains an invaluable tool which will allow us to solve a very large range of problems concerning both internal and external geodynamics (solid, fluid and bio-spheres). The accurate determination of the APWPs of crustal and lithospheric blocks remains one of the main goals that must be pursued by the paleomagnetic community. Based on two examples, one extending from Permian to Present, the other in the Late Proterozoic to Early Paleozoic, I will discuss various aspects of the construction of APWPs and reconstruction of past plate positions. Critical steps involve: 1) how are original paleomagnetic data selected? 2) how are the kinematic models used to transfer data from one plate to the other determined ? 3) how can poles coming from deformed (e.g. rotated) regions be used ? and 4) how good is the geocentric axial dipole (GAD) assumption, which is fundamental for reliable plate reconstructions ? Particular emphasis will be given to this last topic, since the GAD hypothesis has recently been challenged, with suggestions that significant long-term octupolar contributions might have existed from the Precambrian throughout to the early Tertiary. These might account for the low inclinations observed in central Asia in the Cretaceous and early Tertiary, or for the misfits of Pangea (Pangea A or B?). GAD hypothesis appears to be essentially correct and APWPs still have a bright future.
DE: 1724 Ocean sciences
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1560 Time variations--secular and long term
SC: Union [U]
MN: 2004 AGU Fall Meeting