CRETACEOUS AND CENOZOIC PLATE INTERACTIONS ALONG THE CASCADIA MARGIN, PALEOLATITUDES, THE FIXED-HOTSPOT APPROXIMATION, AND TRUE POLAR WANDER

Understanding the history of plate interactions along the Cascadia margin, as well as along the rest of the circum-Pacific margin, requires a method for relating the motion of the Pacific basin plates relative to the surrounding continents. In this session honoring Rick Blakely and Ray Wells we plan to lay out the case for the usefulness of the reference frame in which it is assumed that hotspots are approximately fixed relative to one another (Morgan, 1981; Engebretson et al., 1985). We will present several lines of evidence that indicate that motion between hotspots has been much less than previously proposed by several groups. Moreover, paleomagnetic poles from both the Pacific plate and from the continents indicate several significant episodes of true polar wander during Cretaceous and Cenozoic time, some of which may relate to changes in the regime of global climate. The effect of true polar wander on the interpretation of the paleolatitude framework of North America will be discussed.