HR: 1340h
AN: GP33A-0110    [Abstracts]
TI: Are Steep Normal Magnetic Overprints in the Arctic Related to the Tangent Cylinder during the Cretaceous Normal Superchron?
AU: * Stone, D B
EM: dstone@gi.alaska.edu
AF: Geophysical Institute, 903 Koyukuk Drive University of Alaska, Fairbanks, AK 99775 United States
AB: We have long been puzzled by a pervasive, near vertical, normally magnetized overprint seen in essentially all paleomagnetic data collected in the region of the Brooks Range and Arctic slope of Alaska. Because this overprint is so steep, we concluded that it had to have been impressed on the rocks during Cretaceous time when the geomagnetic pole was located in offshore northwestern Alaska. More recent paleomagnetic results from Northeast Russia show a very similar pattern of very steeply dipping normally magnetized overprints. These results come from locations between 134o and 154o East and between 64o and 70o North in the Sakha republic (Yakutia) and the Magadan Oblast. The age of these overprints is unclear and many have been assigned ages between 180Ma and 140Ma based on the proximity of the Apparent Polar Wander (APW) path for Eurasia to the sampling localities, however many of the sampled localities have circumstantial evidence that they were remagnetized much later than this. It is geologically plausible that the remagnetizations result from tectonic activity associated with the accretion of terranes migrating from the south and the opening of the Arctic Ocean basins. Much of this activity took place within the Cretaceous normal superchron (approximately 80Ma to 118Ma) which would account for the normal remagnetization directions. All the sample locations are within or close to the tangent cylinder for the mean geomagnetic pole representing the Cretaceous APW still-stand. This leads us to ask the question as to whether it is possible that near vertical fields could have been dominant within the tangent cylinder during the Cretaceous normal superchron. We are currently engaged in compiling all the available data on overprinting in northern Alaska and Northeast Russia with the intent of quantifying any trends in the steepness of the overprint with the paleogeographic distribution of the sampling localities. We have already found that the area with steep normally polarized overprints extends beyond the areas described above.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1510 Dynamo: theories and simulations
DE: 1533 Remagnetization
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005