Magnetic model studies of the New York--Alabama Lineament and other magnetic anomalies in West Virginia

This study was undertaken to model possible origins of the magnetic anomalies in the central Appalachian foreland of West Virginia with aeromagnetic total intensity data. Analysis of the areal distribution of residual magnetic anomalies and modeling of of selected residual magnetic profiles were also undertaken. Basement crustal lithology and structure are thought to be responsible for the magnetic anomalies observed in West Virginia. The most prominent magnetic anomaly modeled in the study area is the New York – Alabama lineament (NY-Al). The NY-Al is a regional scale, linear magnetic high that lies along the east margin of the Rome trough in central West Virginia. Preliminary model studies were undertaken of a local magnetic anomaly along the NY-Al in the Gassaway District of Braxton and Clay counties of central West Virginia. Models of a NY-Al source revealed that the center of the magnetic bodies used to simulate the magnetic anomaly can be located no deeper than 20 kilometers below current sea level (at approximately mid-crustal depths as inferred from earlier gravity model studies). Models indicate that the dip of this zone could be anywhere from 32°NW to 27°SE. The magnetic susceptibility has been modeled within the range of 0.0025 to 199.0 cgs units, so that any known lithology could, in theory, be used to represent the NY-Al magnetic source body. The models of the NY-Al source body, however, use the average magnetic susceptibility of a basalt (consistent with the likely lithology of an intrusion along a transform fault zone). Interpretations of residual aeromagnetic data (provided by AGI) reveal the presence of two categories of magnetic anomaly trends. Variations in the magnetic grain of the region are reflected in the form of alignment of residual magnetic anomaly highs and lows (ARMAHLs). Interruptions of anomaly trends are present in the form of the alignment of residual magnetic anomaly terminations (ARMATs). Selected anomalies (both ARMAHLS and ARMATs) are modeled to assess possible geological interpretations responsible for their formation. In addition, the ARMATs and ARMAHLs are superimposed upon inferred and known near surface structures for purposes of adding support to the theory of basement reactivation and subsequent formation of structures, such as the Gassaway dome. Results from the modeling of the residual data reveal that a weathered basement deformation zone or simply basement topography may be used to represent the low amplitude, short wavelength anomalies occupying regions bounded by ARMATs. Regions characterized by relatively low amplitude anomalies within the Rome trough, could not be modeled as preferentially weathered areas of low susceptibility. Instead, residual magnetic anomalies in this area of the trough were successfully modeled by introducing thin sheets of relatively high susceptibility (interpreted as basalt flows) into the interior of the trough.