Linear belts 50–100 km in width of long-wavelength positive magnetic anomalies exceeding 500 nT are observed on continental blocks of the Scotia arc. The most developed is the West Coast Magnetic Anomaly which may be traced for more than 1300 km along the Antarctic Peninsula. Comparison of magnetic profile data after low-pass filtering and reduction to pole reveals a striking similarity between the individual anomaly belts. Correlation of the anomalies with positive gravity anomalies, seismic refraction data and geology indicates that the sources are linear batholiths intruded during Mesozoic/Cenozoic subduction. The anomaly belts are truncated at the block margins reflecting Cenozoic fragmentation of a cuspate convergent margin. An early Cenozoic reconstruction, based on the assumption that the batholiths once formed a continuous curvilinear feature, shows a good alignment of Mesozoic strato-tectonic terrains and is compatible with the known history of Scotia Sea opening.