Mathematics – Logic
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmgp43a..02b&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #GP43A-02
Mathematics
Logic
1520 Magnetostratigraphy, 1527 Paleomagnetism Applied To Geologic Processes
Scientific paper
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 down going 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 pioneering 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. However, in a large number of paleomagnetic studies in the literature, uncertainty related to age (or the exact time window) is very often larger than 10 myr. The result is that small amplitude (<10°) or rapid (b<=10 myr) APW features are often unresolvable. Based on two examples, one extending in the Jurassic and Cretaceous, the other during the Paleocene, I will discuss various aspects of the construction of APWPs and reconstruction of past plate positions using combined magnetostratigraphies. 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. Improved APWP segments document a fast loop during the Paleocene and a fast and abrupt change in plate motion without any significant standstill close to the Late Jurassic/Early Cretaceous boundary. I will discuss for these two period of times some paleo-environnemental and geodynamic aspects, such as the the Paleocene time evolution of vertebrate occurrence or the tree ring growth rate in the polar regions, or the geodynamic consequences of the change in plate motion at around anomaly M16. References: S. Satolli et al. , Earth and Planetary Science Letters 257 (2007) 329-342, M.G. Moreau et al, Earth and Planetary Science Letters 260 (2007) 152-165
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