Discrete segments of the southeast Pacific Ocean crust were subducted beneath the Antarctic Peninsula in Late Cretaceous and Cenozoic time. The segment boundaries of the subducted ocean crust are reflected in the overlying continental crust by transverse megafractures. These are usually obscured by contemporaneous magmatism but may be revealed by later fault movements. The transverse fracture zones divide Graham Land and its offlying islands into segments that have different histories of magmatism, uplift and erosion, and postorogenic sedimentation. Metalliferous mineralization is controlled, in part, by the transverse fracture zones.