Archeomagnetic and paleomagnetic dating

Early in the 20th century, work by David, Brunhes and Mercanton showed that many rocks were magnetized antiparallel to the field. His intent was to test his theory that the geomagnetic field was related to the Earth's rotation, a theory that he ultimately rejected; but the astatic magnetometer became the basic tool of paleomagnetism and led to a revival of the theory of continental drift.

Japanese geophysicist Motonori Matuyama showed that the Earth's magnetic field reversed in the mid-Quaternary, a reversal now known as the Brunhes-Matuyama reversal. Alfred Wegener first proposed in 1915 that continents had once been joined together and had since moved apart.

The record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences (magnetostratigraphy) provides a time-scale that is used as a geochronologic tool.

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Presently, such application is widely used for dating within a recent period for archeological structures ( Thellier, 1938; Le Goff et al., 2002 ) or lava flows ( Tanguy et al., 2007 ).

Van der Voo, 1988, 1990; Torsvick et al., 2012 ), or to determine more or less local tectonic rotations (e.g.

in the Western Alps – Westphal, 1973; Henry, 1992; Thomas et al., 1999; Maffione et al., 2008 ).

Paleomagnetism continues to extend the history of plate tectonics back in time and are applied to the movement of continental fragments, or terranes.

Paleomagnetism relied heavily on new developments in rock magnetism, which in turn has provided the foundation for new applications of magnetism.

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