Deep resistivity results from New York and Virginia

Surface resistivity measurements in the Adirondacks of New York show the anorthosite mass to be highly resistive and homogeneous. A two-layer model with a lower layer resistivity of 25,000 ohm-m fits the data, but a three-layer model shows that layers with resistivities of 105 ohm-m could exist at a great depth. Dipole separations went out to 47 km, making interpretation possible for depths of several kilometers. Resistivity results from northern Virginia reflect lateral changes in the geology. Apparent resistivities at comparable dipole separations vary from 50 to 5000 ohm-m over a 55-km traverse.