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Adam Maloof - Research

True Polar Wander

True polar wander (TPW) is defined as the motion of the entire solid earth with respect to the spin axis, while the spin axis remains fixed with respect to the solar system. One can think of TPW as Earth's attempt to maintain rotational equilibrium while plate tectonics and mantle convection change the distribution of mass within the planet.


In the figure above, (A) shows how Earth departs from a perfect spherical shape just because it rotates and may deform on long time scales.  It is this equatorial bulge that sticks out into the solar system, interacts with the moon and sun and planets, and causes Earth's axis to wobble (not TPW).  The beetle on a sphere (B) depicts Gold's and Goldreich & Toomre's famousnvision of even the tiniest mass anomaly (beetle) driving true polar wander on a rigid sphere.  It turns out that Earth's viscosity and the size of its rotational bulge partly set the speed limit for TPW (D).  However, it is Earth's shape after removing the effects of rotation that determines whether TPW will occur.  If the non-hydrostatic figure is football-shaped (C), Earth will be particularly susceptible to rapid TPW about the minimum moment of inertia.

From 1998-2004Galen HalversonMatthew Hurtgen and I conducted an integrated stratigraphic, geochemical and paleomagnetic study of Tonian and Cryogenian rocks in Svalbard, Greenland, and the Mackenzie Mountains (Canada).  This work revealed a pair of 60 degree paleomagnetic rotations coincident with distinctive changes in sea level and the carbon isotope composition of carbonate (d13C) across the Bitter Springs Stage (orange highlight in figure to right). We proposed a true polar wander origin for these events, and published our results in GSA Bulletin in 2006.


Since 2006, Nick Swanson-Hysell and I have mounted a similar project in Central Australia (below) with funding from NSF.  After four field seasons and thousands of carbon-isotopic and paleomagnetic analyses, we think that the Bitter Springs Formation provides a positive test of the TPW hypothesis, and we presented these results at the Geological Society of London Fermor Meeting 2009 in Scotland.