Model for Plate Tectonics and for the Earth’s Magnetic Field

Model for:----- Plate Tectonics------ and for the ------Earth's Magnetic Field----------------------Full Text Download---------

Plate tectonics theory, which revolutionized our understanding of the earth and successfully describes the motions of the continents, is incomplete. Despite the extensive research there is no adequate explanation for the causes of the plate motions. The widely held consensus, heat-related mantle convection provides the energy for the plate movements, can easily be tested. The physics of the convection is known, the motions of the plates are well defined, and the viscosity of the mantle is known with the required accuracy. Using these data allows one to determine global convection patterns. But putting the convection cells under the plates results in many trouble spots. The discrepancies could be resolved by reducing the viscosity of the mantle. The lower viscosity would allow more flexibility between the convection cells and plates and the observed kinematics of the plates could be reproduced. However, the reduction of mantle viscosity results in smaller convection cells with insufficient size. This paradox of mutually exclusive observations, high viscosity unable to explain the plate motions and low viscosity unable to produce the required size of the convection cells, suggests that mantle convection models do not provide a credible explanation for plate tectonics and that it is time to change the paradigm.

It is well established that both CO2 and H2O survive subduction. These recycled materials eventually produce carbonate and hydrous melts in the mantle. This prediction can not be tested because seismic tomography at the current technological level is unable to detect a low viscosity layer at 660 km with thickness of few kilometers. The presence of a small percentage of carbonate melt (1-3%) can transport matter extremely fast by dissolution and precipitation processes and thereby reduce the apparent viscosity of the mantle by ten orders of magnitude or more. The existence of low viscosity layer is inferred in accordance with geological and geophysical observations. This low viscosity layer allows the development of differential rotation between the 660 km outer shell and the rest of the earth. Temperature differences inside the Earth diffuse electrons (or holes) resulting in a thermally-induced, inhomogeneous charge distribution. The charge builds up on the cold end and creates electric field inside the earth. This static electricity and the coupling at 660 km generates a magnetic field. This simple dynamo model is consistent with the identified magnetic field of the Moon in its early history and the lack of plate tectonics and intrinsic magnetic field of Venus.

Based on the current field, the outer 660 km shell should rotate faster than the rest of the earth. Assuming that the westward movement of the dipole field [0.050/y.] represents the rotational difference developed at 660 km, the charge required to generate the current field is calculated. The calculated excess charge [6.7x10-7 Ccm-3] is on the same order of charges generated by friction. Using the charge density required to produce the current field and modifying the rotation of the 660 km outer shell in accordance with the observed changes in the Length of the Day the calculated strength of the magnetic field reproduces the observed reduction of the field. The detected lunar cycles in the geomagnetic field can also be explained by the secular changes in the rotation of the earth caused by the moon. By modifying the angular velocity of the earth’s rotation through mass redistribution on the surface, climate changes should also have affected the strength of the magnetic field. If the polarity of the field is normal than a glaciation period should increase the strength of the field, while a deglaciation period should reduce the strength of the field. Correlation between ice ages and the strength of the magnetic field is consistent with the proposed mechanism.

Reversing the field would require to change the sign of the differential rotation which is affected by the tidal drag effect and mass redistribution. Thus Reverse to Normal (R-N) reversal should result from global cooling while N-R reversals should occur resulting from tidal drag which might be associated with global warming. The magnetic field shift observed at the Brunhes-Matuyama reversal would require about a 140-m reduction of the global sea level, which is in the range of the known fluctuation of the eustatic sea level. It is suggested that the preferred longitudes for the virtual geomagnetic poles are along the subduction zones because the resistance against the differential rotation is the strongest. This is a strong indication that the field is not generated in the inner core.

Jozsef's Home Page ----------------------------- Research