Abstract: Crustal Scale Gravity and Magnetic Models Along a Transect Across the Central Appalachians of West Virginia

J. F. Morgan, T. H. Wilson

The origins of gravity and magnetic anomalies along a transect across the central Appalachian foreland of West Virginia are evaluated through inverse modeling. The gravitational influence of basement geometry and Paleozoic sediment distribution was incorporated in the gravity models using published surface geologic maps, limited borehole data, and nearby seismic profiles. The transect is dominated by a major regional scale gravity anomaly that rises from approximately -80 milligals along the West Virginia/Virginia border to a high of -46 milligals in central West Virginia and drops farther northwest to approximately -60 milligals. Several magnetic anomalies of up to 600 nanoteslas in magnitude occur along the profile.

Calculations reveal that gravity anomalies along the profile are not simply related to the distribution of Paleozoic sediments. Gravity models derived from the data indicate that gravity anomalies are due in large part to variations in the thickness of the crust from 55 km to just under 30 km. The potential role of intra-crustal layering interpreted from seismic refraction data collected in the Appalachians is also modeled. The magnetic model indicates that the major linear anomaly associated with the New York-Alabama Lineament can be explained by susceptibility contrasts concentrated in the lower half to lower two-thirds of the crust. Anomalies with more limited strike lengths are modeled by more localized regions of susceptibility contrast in lower and mid-crustal levels. Magnetic b dies are generally not associated with specific bodies in the gravity model suggesting that they result from different episodes of magnetization in rocks of similar lithology.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas