Two-dimensional models are presented for the crustal structure of the Antarctic Peninsual, a Mesozoic-Cenozoic magmatic arc on the southeast Pacific margin. The models are constrained by measured rock properties. The West coast Magnetic Anomaly (WCMA) is caused by a zone of mafic plutons which is 70--150 km wide and over 1500 km long. In modelling of Bouguer anomalies, isostatic compensation is maintained by crustal thickness variations. The model Moho is deepest (35 km) beneath the mid-Cretaceous axis of the arc and shallowest (<20 km) beneath a Late Cenozoic marginal basin. Positive isostatic residual gravity anomalies are associated with the WCMA and a mafic terrane in the Mesozoic accretionary complex. Three broad areas of consistent crustal structure are identified. The junctions of these areas are sinistral fault zones which displace the curvilinear magnetic, physiographic, and gravity patterns by several tens of kilometers. ¿ American Geophysical Union 1990