GRAVITY AND MAGNETIC SURVEY OF THE LAKE CHAMPLAIN

Several hundred gravity and magnetic measurements were made in the Lake Champlain Valley between 44.70 and 45.00 degrees north latitude and 73.40 and 73.65 degrees west longitude. These measurements were used to construct gravity and magnetic maps of the survey area. The gravity and magnetic maps show gravity and magnetic anomalies that originate in the Precambrian basement and correlate with surface faults in the overlying Cambro-Ordovician sedimentary rocks. This suggests that the faulting in the sedimentary rocks is controlled by faulting in the Precambrian basement. When comparing the gravity and magnetic maps, it is apparent that both maps show the same general trend of anomalies. The rocks causing the gravity highs and lows are also causing the magnetic anomalies.

Two prominent gravity highs occur in the area: the Plattsburgh and Sciota anomalies. The Plattsburgh gravity high is circular shaped and lies just north of Plattsburgh. Modeling of this anomaly indicates a cylindrical gabbro intrusion 1.5 km in diameter satisfies the observed gravity anomaly. This anomaly has several faults across it suggesting that doming upwards gave rise the faulting in the Paleozoics.

The Sciota gravity high is a northeast-southwest elliptically shape gravity anomaly with steep gradient along the southeast flank. This steep gravity gradient is associated with a fault in the Paleozoics. Modeling of this anomaly indicates a thin slab 2 km wide, 4 km long and 600 meters thick satisfies the anomaly.