On-line version
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.
On-line version
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.
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 critically 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