Paleomagnetic Data from the Okhotsk-Chukotka Volcanic Belt: Little or No Relative Motion with Respect to North America?

By

D.B. Stone (Geophysical Institute, University of Alaska, Fairbanks), K. Anderson (Macquarie University, Australia), P.W. Layer (Geophysical Institute, University of Alaska, Fairbanks), and P. Minyuk (N.E. Interdisciplinary Research Institute)

The Okhotsk-Chukotka volcanic belt extends from the Bering Strait to northeastern China, roughly following the northern coast of the Sea of Okhotsk. Recent Ar/Ar ages have been determined for this belt, mostly from mineralized areas, but all indicate that the belt was constructed between about 65Ma and 90Ma. This is a time when the inboard terranes that now form most of Alaska and Northeast Russia were largely in-place, but with considerable relative motions occurring, and some of the most outboard terranes were still moving northwards on the plates of the Pacific Ocean. To reconstruct the paleogeography for this time it is necessary to have reliable paleomagnetic data from both the individual terranes and from a “backstop” against for comparison. The two obvious backstops are the North American and Siberian platforms, but the data sets don’t match very well.

In this study we determined paleomagnetic pole positions for volcanic rocks from the Okhotsk-Chukotka volcanic belt collected from areas near Provideniya and Lake Elgygytgyn in Chukotka, and near the Ola and Yana rivers in the Magadan district. When these poles are compared with various Virtual Geomagnetic Pole (VGP) estimates for Siberia and North America it is seen that there are some marked discrepancies. However, the best-fit reconstruction appears to indicate that the Okhotsk-Chukotka volcanic belt was closely related to, if not part of the North American platform about 80 Ma ago. This leaves open the question of where the boundary between the Eurasian and North American plates was located at this time.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.