PLATE MOTIONS IN THE NORTH PACIFIC - THE 43 MA NONEVENT

The Hawaiian-Emperor seamount chain in the North Pacific Ocean is commonly considered to have been produced by motion of the Pacific plate over a hotspot. If the hotspot is assumed to have remained fixed in a mantle frame of reference, the 60 degrees change in trend between the Hawaiian and Emperor portions of the chain results from a change in motion direction of the Pacific plate relative to the mantle at 43 Ma, during Middle Eocene time. Such a large and abrupt direction change should result in significant plate reorganizations and tectonic events in the Pacific and surrounding plates, but no evidence for these events can be found. In addition, in this paper it is shown that there were no changes in relative plate motions between Pacific-area plates that can be associated with the Hawaiian-Emperor bend. This is done by calculating motion of the Pacific, Farallon, and Kula plates relative to Asia and North America using the plate circuit Farallon-Pacific-Antarctica-Africa-North America-Asia. With no major regional tectonic event at the time of the bend, it is suggested that there was no plate reorganization at 43 Ma and that the Emperor portion of the seamount chain was formed by a nonstationary hotspot.