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This chapter briefly summarizes the basic principles and methods of paleomagnetic research that are germane to the geophysical framework of North America. Under the assumption that the geomagnetic field is approximated by a geocentric axial dipole source, paleomagnetic data are useful for determining paleolatitudes, displacements, and azimuthal rotations of crust during the distant past. As confirmed by paleomagnetic data, the time-averaged geomagnetic field has maintained the configuration of a geocentric dipole aligned with the Earth’s rotation axis since 5 Ma. Paleomagnetism and paleoclimatic evidence from older rocks, when corrected for sea-floor spreading, strongly support the axial dipole hypothesis back to Jurassic time; evidence from Proterozoic rocks is also supportive. The major pitfalls in determining valid paleomagnetic poles are insufficient sampling to ensure complete time-averaging of the nondipole field, and incomplete removal of magnetic overprints that mask the primary depositional remanent magnetization. These problems can be avoided through careful design of the sampling scheme, thorough analysis of the components of magnetization, and application of conventional reliability tests.

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