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Aeromagnetic anomalies over the Carolina Slate belt near Roxboro, North Carolina, are influenced by geologic structure and regional metamorphism. Anomaly amplitudes diminish with the transition from greenschist- to amphibolite-facies rocks along a north west-trending metamorphic gradient. The northeast-trending Virgilina synclinorium is the principal structure in the area. A greenschist-facies metasedimentary rock unit is the principal magnetic-anomaly source in the northeast part of the synclinorium. Magnetization of this unit appears to diminish in a southwesterly direction along the structure, apparently because of the alteration of magnetite to hematite by oxidation.

Field-intensity profiles crossing linear anomalies were compared with profiles computed for two-dimensional models to determine the subsurface configuration of the Virgilina synclinorium. These comparisons indicate that the greenschist-grade metasedimentary rocks extend to depths of at least 2.5 km along the axis of the synclinorium. This implies that the amphibolite-greenschist isograd surface, which is exposed approximately 8 km northwest of the synclinorium axis, cannot dip toward the southeast at less than 20 degrees.

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