HR: 10:20h
AN: U32A-01    [Abstracts]
TI: Fast Apparent Polar Wander in the Phanerozoic: True PW or Fast Drift Rates?
AU: * Van der Voo, R
EM: voo@umich.edu
AF: University of Michigan, Dept. Geological Sciences, Ann Arbor, MI 48109-1063 United States
AU: Bazhenov, M L
EM: palmag@online.ru
AF: Russian Academy of Sciences, Geological Institute Pyzhevsky Lane 7, Moscow, 109017 Russian Federation
AU: Levashova, N M
EM: palmag@online.ru
AF: Russian Academy of Sciences, Geological Institute Pyzhevsky Lane 7, Moscow, 109017 Russian Federation
AU: Degtyarev, K E
EM: palmag@online.ru
AF: Russian Academy of Sciences, Geological Institute Pyzhevsky Lane 7, Moscow, 109017 Russian Federation
AU: Mikolaichuk, A V
EM: palmag@online.ru
AF: National Aacademy of Sciences, Geological Institute 30 Erkindyk Av., Bishkek, 720481 Kyrgyzstan
AU: McCausland, P J
EM: pjam@umich.edu
AF: University of Michigan, Dept. Geological Sciences, Ann Arbor, MI 48109-1063 United States
AB: It is well known that in Mesozoic and younger times, continental drift velocities have been generally less than 8 cm/a, although the northward drift of India just before its collision with Tibet was an exception at more than 15 cm/a. In the Paleozoic, however, fast episodes of APW seem more frequent, and in this talk we report on Ordovician rapid south-to-north drift of the North Tien Shan area in Kyrgyzstan. While radiometric age dating of the rocks involved will not be completed until mid-2005, the presently existing age constraints and the observed changes in paleolatitude imply velocities approaching 20 cm/a, given that paleolatitudes change from 71 degrees in the Arenig to 9 degrees in the Caradocian. Fold- and intraformational conglomerate tests allow us to ascertain the (near-?)primary nature of the remanences. This fast rate resembles the significant paleolatitude changes of Baltica in Ordovician times, and raises the question whether it is related to an episode of large-scale true polar wander (TPW) or whether plate velocities were very high for only these continental blocks. TPW can be distinguished from fast plate movements because every APWP from all continents should show it and it must occur for all continents during the same interval of time. It turns out that for Gondwana and Laurentia, the rate of APW is not unusually high during the Ordovician, and that for this time interval we can therefore conclude that TPW is an unlikely explanation. Previous suggestions that fast TPW occurred in the Cambrian are, similarly, not borne out by global synchroneity of fast APW. For the Neoproterozoic, on the other hand, the database is still too scarce to reach definitive solutions.
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1530 Rapid time variations
DE: 1560 Time variations--secular and long term
SC: Union [U]
MN: 2004 AGU Fall Meeting