MAGNETIC CONSTRAINTS ON THE SOUTHWESTERN CONTACT OF THE BOTTLE LAKE IGNEOUS COMPLEX NEAR PASSADUMKEAG MOUNTAIN, ME
Total magnetic field data were collected using a proton precession magnetometer at 160 m (0.1 mi) intervals along a highway, a network of logging roads, and a new access road for the installation of wind turbines along the crest of Passadumkeag Mountain. Using two sensors, we sampled at different elevations to be able to compute vertical magnetic gradients, and monitored time variation in the local magnetic field at base stations midway along two of our three transects. Following the field campaign, the data were plotted according to latitude (for the S-N sections) and longitude (for the W-E section) and compared to the regional magnetic gradient reduced by 53000 nT extracted from the ME state magnetic map.
Little temporal magnetic field variation was noted and only the longer W-E transect needed correction for time, with deviations up to 30 nT. A positive magnetic anomaly nearly 100 nT from the regional trend, accentuated on the vertical gradient plot, suggests that the contact lies near the western end of the W-E transect. Positive anomalies near the southern ends of the two S-N sections, approximately 6 km apart, suggest that the southern contact of the pluton lies high on the slope of Passadumkeag Mountain. On the easternmost transect, the anomaly is 300 nT greater than the regional trend, and on the westernmost transect, the anomaly is nearer 50 nT, but the vertical gradient is reversed. Further modeling will explore the geometry and magnetic properties of subsurface bodies that can account for such anomalies.