New high-resolution aeromagnetic anomaly data from the central Antarctic Peninsula reveal a magnetic signature typical of a magmatic arc system. Analysis of the new aeromagnetic map, together with susceptibility data and 2.5-dimensional modelling support the interpretation of the Pacific margin anomaly as reflecting a mid crustal batholithic province consisting of magnetite-rich plutons. Examination and analysis of the magnetic anomaly map shows variations in magnetic character along the Antarctic Peninsula. These variations, in conjunction with geological and other geophysical data sets, are interpreted as indicating distinct segments of continental crust. Of particular importance is the identification of three distinct areas of basement on the eastern side of the Antarctic Peninsula, of which the central area (66 ¿S to ~68¿) appears to be gneissic basement at a relatively high crustal level. To the north of 66 ¿S, the basement is formed of late Palaeozoic-?Triassic accretionary material, and to the south of ~68 ¿S the basement is unknown. Segmentation is a common feature of arcs worldwide, and previous studies of the Antarctic Peninsula have linked the continental segmentation to the arrival of a series of ridge crests at the subducting Pacific margin. This study indicates that the major segmentation of the continental crust is linked to the pre-Cretaceous crustal structure of the peninsula, which was subsequently modified by extension during the Cenozoic. It is suggested that this Cenozoic extension was caused by a reduction in plate convergence rates at two distinct times, rather than the arrival of ridge segments at the trench, as previously proposed. ¿ 1999 American Geophysical Union