HR: 10:35h
AN: U32A-02    [Abstracts]
TI: Apparent polar wander paths and relative paleolongitude in supercontinents
AU: * Evans, D A
EM: dai.evans@yale.edu
AF: Yale University, 210 Whitney Ave, New Haven, CT 06520-8109 United States
AB: A popular misconception of the paleomagnetic method is that it provides no constraints on relative paleolongitude. Whilst it is indeed true that axisymmetry of the time-averaged geomagnetic field allows only paleolatitude comparisons between two or more continents when a set of paleomagnetic poles from a single geological age are compared, it is also valid that in the special cases of continents travelling together as part of a supercontinent, or during episodes of rapid true polar wander, then in these instances reconstruction of the continents to their correct paleogeography will superimpose their apparent polar wander (APW) paths. Conversely, if superposition of APW paths results in continental juxtapositions that are geologically reasonable for the time interval under consideration, then paleomagnetism can thereby generate precise constraints on relative paleolongitude. In 1956, Irving and Runcorn independently utilized this method to restore the north Atlantic Ocean, whose opening, after all, is primarily a separation of longitude. Pre-Pangean continental reconstructions rely solely upon continental paleomagnetism for quantitative precision. Recent methodologies have adopted the "closest-approach" technique for reconstructing Proterozoic supercontinents, but this ignores the power of relative paleolongitude constraints provided by the APW-superposition method. Examples from the Paleoproterozoic supercontinent Nuna and Neoproterozoic Rodinia, as well as hypothesized episodes of rapid true polar wander within the Proterozoic-Cambrian transition, will illustrate the superiority of APW manipulation in deep-time reconstructions.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1520 Magnetostratigraphy
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1532 Reference fields (regional, global)
DE: 1560 Time variations--secular and long term
SC: Union [U]
MN: 2004 AGU Fall Meeting