Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: chris on 31/12/2009 12:16:43
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I was asked by someone the other day whether tectonic activity could account for changes in the Earth's magnetic field, specifically in terms of things like pole reversal.
My immediate answer was no, on the observational grounds that pole reversal occurs on a roughly 100,000 year timescale whereas tectonics occurs on a multi-million year timescale. The two cannot be directly linked owing to this timescale disparity.
However, in terms of the broader picture, I'd be interested to know whether there are any magnetic consequences of continental drift?
Chris
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Features in the Earth's crust surface can locally distort the magnetic field ...
Magnetic declination varies both from place to place, and with the passage of time. As a traveller cruises the east coast of the United States, for example, the declination varies from 20 degrees west (in Maine) to zero (in Florida), to 10 degrees east (in Texas), meaning a compass adjusted at the beginning of the journey would have a true north error of over 30 degrees if not adjusted for the changing declination.
In most areas, the spatial variation reflects the irregularities of the flows deep in the earth; in some areas, deposits of iron ore or magnetite in the Earth's crust may contribute strongly to the declination.
http://en.wikipedia.org/wiki/Magnetic_declination
So there is a force applied to the iron in the crust by Earth's magnetic field e.g. ...
http://en.wikipedia.org/wiki/Paleomagnetism
although I doubt this magnetic force is strong enough contribute to continental drift.
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I would suspect that the answer is a resounding "NO" After all, the process that are believed to cause plate tectonics are mantle processes. The electrical-magmatic field is a result of the same process - if the core also has some of these processes in common with the mantle. But that is an unknown "if"
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I agree with JimBob and vote for the "resounding "NO".
Other than the time periods and the fact that plate tectonics is driven by mantle processes, as has been already noted- the crust is simply too thin to believe that movements of the plates has any causative effects on magnetic reversals. The prominent magnetic "zebra" stripes on each side of mid-oceanic ridges, which are caused by magnetic reversals, also strongly suggests that plate tectonics exert no control over the magnetic field.
However, the magnetic field is a great tool for finding the location of rocks in the past. Latitude, longitude and age can often be determined by the orientation and inclination of the original magnetic field in rocks when they were formed. Snowball Earth advocates love this stuff.