Paleomagnetic studies employ the phenomenon in which magnetic minerals, such as magnetite, record the Earth's magnetic field at the time of solidification of magma or lava (Curie temperature). [image computer simulation of Earth's magnetic field] This magnetic record of prior magnetic orientation is termed thermal remnant magnetism (TRM) for igneous and metamorphic rocks, and detrital (depositional) remnant magnetism (DRM) for sedimentary rocks in which individual grains of magnetic minerals align with the magnetic field during their deposition as sediments. Chemical remnant magnetism (CRM) can be detected in some rocks as magnetic grains are deposited from circulating solutions.
Paleomagnetism has been employed to:
● map sea floor spreading as basaltic oceanic crust spreads from its line of formation along mid-ocean ridges, providing strong empirical support for theories regarding plate tectonics as a mechanism for continental drift [diagram, magnetic stripes, ridges, ridges 2, ridges 3]
● map polar wandering
● determine past global positions of ancient rock formations or terranes (when combined with radiometric determination of the age of a rock formation)
● constraining possible ages for rocks and for geologic processes
● reconstructions of deformational histories of segments of the crust.
: e-Book Magnetic Domains to Geologic Terranes (pdf) : e-Book Lectures in Paleomagnetism (html or pdf) : paleomagnetism analyses USGS : The Geodynamo :
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