AN INTERPRETATION OF GRAVITY ANOMALIES IN PENNSYLVANIA

A simple Bouguer gravity map of Pennsylvania of 1:500,000 scale and a 2 mGal contour interval is superimposed on the new geologic map of Pennsylvania of the same scale to study the relationship of the regional gravity anomalies to the geology of Pennsylvania. Nine gravity anomalies are outlined and their interpretation is discussed by Lavin (1999). Four gravity anomalies are located in the Appalachian Plateau Province and show no obvious correlation with surface geology. These anomalies have low magnitudes and gradients and probably have a deep-seated origin.

In eastern Pennsylvania, the most interesting anomaly is the Scranton gravity high extending from Albany, NY to Harrisburg, PA. This anomaly is flanked by gravity lows on the north and south, which may be related to the gravity high. The Scranton gravity high lies in an area where the trend of the Appalachian changes from northerly in New England to west in Pennsylvania.

In southeastern Pennsylvania, there is an abrupt increase in gravity from -50 mGals to +20 mGals. This step gradient marks the edge of the North American Craton and could represent a suture zone between colliding plates in late Paleozoic time (Kane 1982). A major increase in density contrast south of the zone can account for the anomaly.