True Polar Wander
- R. D. Cottrell and J. A. Tarduno, Late Cretaceous True Polar Wander: Not So Fast,
Science, 288, 2283, 2000.
Using recalculated paleopoles from seamount anomaly modeling (SAM), Sager and
Koppers (2000) proposed an episode of rapid Late Cretaceous true polar wander (TPW). A
critical review of the data used, however, suggests that Sager and Koppers have
underestimated the effects that errors and data selection have on inferences of TPW and
that they may not have adequately taken into account alternative explanations consistent
with error sources, modeling uncertainties, and the geology of the Pacific Ocean basin.
Further, their TPW hypothesis fails a test based on paleomagnetic data from a
well-studied, highly regarded pelagic sedimentary section of the same age.
- J. A. Tarduno and A. V. Smirnov, Stability of the Earth with respect
to the spin axis for the last 130 million years, Earth and Planetary Science
Letters, 184, 549-553, 2001.
Recently continental paleomagnetic data rotated into a hotspot reference frame have been used to suggest the Earth rotated 18° with respect to the spin axis
at 110 Ma. We test this true polar wander (TPW) hypothesis using paleomagnetic data from widespread granitic rocks of cratonal North America. These
data conflict with TPW predictions leading to rejection of the hypothesis. The calculated polar displacement is instead consistent with motion of the
Atlantic hotspots during the mid-Cretaceous. This analysis suggests that the time-averaged position of the spin axis has deviated by no more than ~5° over
the last 130 million yr, indicating that mantle mass heterogeneities have not changed rapidly enough to drive TPW.
- J. A. Tarduno and A. V. Smirnov, Response to Comment on ``Stability of the Earth with respect to the spin
axis for the last 130 Million Years'' by P. Camps, M. Prevot, M.
and P. Machete, in press, Earth and Planetary Science Letters.
True polar wander, the rotation of the entire Earth with respect to the
spin axis, remains as fascinating a geophysical possibility today as it
was when considered by Goldreich and Toomre in 1969 (Goldreich and Toomre, 1969).
But as emphasized by Tarduno and Smirnov (2001), the
plausibility of any specific true polar wander (TPW) event depends
on the frame of reference employed. This is especially true when
considering the Mesozoic to recent, because some studies have defined
TPW using a reference frame defined by fixed hotspots (e.g.
Morgan, 1981; Andrews, 1985). If hotspots move in the mantle as part of
larger scale convection, as has been indicated in a host of recent
investigations (e.g. Tarduno and Gee, 1995; Cande et al., 1995; Tarduno and Cottrell,
1997; Steinberger and O'Connell, 1998; DiVenere and Kent, 1999), this
definition of TPW is invalid.
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Last update: May 1, 2002