Low-Frequency Magnetotelluric Survey of New England.
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH AND PLANETARY SCIENCES
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Magnetotelluric data with a broad range of frequencies 0.01 to 0.000001 Hz from an 11-station array in Vermont, New Hampshire and Massachusetts are presented. A statistical method is developed in order to estimate apparent resistivity tensor values when the magnetic fields are highly correlated. Observations of electric fields parallel to the structural trends N to NE result in apparent resistivity values comparable to those produced by assuming the Cantwell-McDonald conductivity distribution in the mantle, and different crustal conductivities at different locations. Upper mantle conductivities for the preferred models agree with measurements in other continental areas. Because the heat-flow is well known in New England, an upper limit may be put on the temperatures in the upper mantle, and the accuracy of using conductivity measurements on olivine as a thermometer for the mantle may be tested. The upper mantle is not warm enough to produce the observed conductivity with very pure olivine. As extrinsic conduction mechanism must be important in the upper mantle.
- Geology, Geochemistry and Mineralogy