On pole position: causes of dispersion of the paleomagnetic poles behind
apparent polar wander paths
Abstract
Paleomagnetic poles used to compute apparent polar wander paths (APWPs)
are strongly dispersed, which was recently shown to cause a large
fraction (>50%) of these poles to be statistically
distinct from the APWP to which they contributed, suggesting that
current statistical approaches overestimate paleomagnetic resolution.
Here, we analyze why coeval paleopoles are so dispersed, using the
paleopoles behind the most recent global APWP and a compilation of
paleomagnetic data obtained from <10 Ma volcanic rocks
(PSV10). We find that paleopoles derived from sedimentary rocks, or from
data sets underrepresenting paleosecular variation (PSV), are more
dispersed and more frequently displaced. We show that paleopoles based
on a smaller number of paleomagnetic sites are more dispersed than poles
based on larger data sets, revealing that the degree to which PSV is
averaged is an important contributor to the pole dispersion. We identify
as fundamental problem, however, that the amount of paleomagnetic data
used to calculate a paleopole, and thus the dispersion of coeval
paleopoles, is essentially arbitrary. We therefore explore a different
approach in which reference poles of APWPs are calculated from
site-level data instead of paleopoles, thereby assigning larger weight
to larger data sets. We introduce a bootstrap-based method for comparing
a collection of paleomagnetic data with a reference data set on the same
hierarchical level, whereby the uncertainty is weighted against the
number of paleomagnetic sites. Finally, our study highlights that
demonstrating smaller tectonic displacements requires larger
paleomagnetic data sets, and that such data sets can strongly improve
future APWPs.