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Preferred reversal paths caused by a heterogeneous conducting layer at the base of the mantle

University of British Columbia

Paleomagnetic data from sedimentary and volcanic rocks suggest that the positions of the Virtual Geomagnetic Pole (VGP) during polarity reversals over the past few million years are confined to longitudes through the Americas and Asia. In this study I examine the possibility that lateral conductivity variations in the lowermost region of the mantle contribute to the geographical distribution of the reversal paths. The conductivity model consists of a thin layer of material with variable electrical properties which accumulates in the core-mantle boundary region. The pattern of conductivity relies on the geodynamic predictions of the boundary topography and is in good agreement with the seismological observations of heterogeneities at the core-mantle boundary. Temporal variations in the dipole field during a reversal generate electric currents in the conductive layer, which in turn produce a secondary magnetic field. Superposition of the secondary field on a transition field affects the declination and inclination of the magnetic field at the surface and thereby changes the position of the V G P during a reversal. My results predict preferred reversal paths over North America for uniform sampling of testing sites. This corresponds to one preferred path previously observed in the geological records. In addition, preferred paths over the Americas and Asia are predicted when using the same testing sites as the paleomagnetic database, compatible with the distribution of paths given by the observations.

Thesis/Dissertation

application/pdf

2009-11-20

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http://hdl.handle.net/2429/15332

Oceanography

University of British Columbia

UBCV

DSpace