Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis

摘要

Using the geometry and ages from 12 Pacific seamount chains, we have determined two new absolute plate motion models that now extend our self-consistent and high-resolution models with covariance estimates back to 145 Ma. The WK08-A model maps the full uncertainty in the age progressions into uncertainties in rotation opening angles, yielding a relatively smooth plate motion model. The WK08-G model relaxes the mapping of age uncertainties in order to better isolate secondary geometry changes seen along many coregistered chains. Both models have been used to assess the viability of the fixed hot spot hypothesis in the Pacific. In determining the models, we found that only a small group of age samples had to be discarded on the grounds that they were discordant with the dominant trends. We were able to connect plate motions for pre- and post-Emperor age intervals by including the Ratak-Gilbert-Ellice and Musicians trails in our analysis. However, as no active hot spot locations exist for the older chains, their inclusion adds additional model parameters. Both age and geometry misfits increase with age, reflecting the observed increase in age uncertainties and the general widening of trails. Secondary (and short-lived) changes in absolute plate motion mapped in WK08-G appear to correlate with the timing and sense of motion of known Pacific Rim tectonic events. Analysis of interchain distances between coeval samples from the Hawaii and Louisville chains suggests possible discrepancies during the older Emperor stage that are compatible with predictions of hot spot drift. We computed a new apparent polar wander path for the Pacific and found a high degree of correspondence with paleomagnetically derived paths, as long as solutions allowing for anomalous skewness were included in the latter. Our polar wander path suggests that there might have been some true polar wander during the Emperor stage, complemented by a smaller amount of hot spot drift than otherwise required. We show that chain geometries and ages, combined with future paleolatitude determinations from additional sites and chains could enable an observation-based description of both hot spot and plate motions without relying on predictions of hot spot drift derived from mantle flow calculations.