APPARENT AND TRUE POLAR WANDER AND THE GEOMETRY OF THE GEOMAGNETIC FIELD OVER THE LAST 200 MYR

Abstract

We have constructed new apparent polar wander paths (APWPs) for major plates over the last 200 Myr. Updated kinematic models and selected paleomagnetic data allowed us to construct a master APWP. A persistent quadrupole moment on the order of 3% of the dipole over the last 200 Myr is suggested. Paleomagnetic and hot spot APW are compared, and a new determination of ``true polar wander'' (TPW) is derived. Under the hypothesis of fixed Atlantic and Indian hot spots, we confirm that TPW is episodic, with periods of (quasi) standstill alternating with periods of faster TPW (in the Cretaceous). The typical duration of these periods is on the order of a few tens of millions of years with wander rates during fast tracks on the order of 30 to 50 km/Myr. A total TPW of some 30° is suggested for the last 200 Myr. We find no convincing evidence for episodes of superfast TPW such as proposed recently by a number of authors. Comparison over the last 130 Myr of TPW deduced from hot spot tracks and paleomagnetic data in the Indo-Atlantic hemisphere with an independent determination for the Pacific plate supports the idea that, to first order, TPW is a truly global feature of Earth dynamics. Comparison with numerical modeling estimates of TPW shows that all current models still fail to some extent to account for the observed values of TPW velocity and for the succession of standstills and tracks which is observed.