The Marie Byrd Land volcanic province consists of a regionally extensive foundation of subhorizontal alkaline basaltic rocks, surmounted by 18 shield volcanoes of predominantly trachytic and other felsic compositions. Eleven of the felsic volcanoes occur in three N-S and E-W oriented chains. In each of these, chronologic data and morphology suggest systematic migrations of felsic activity along linear paths 90--154 km long. Basaltic rocks show no migration patterns, although they are the most abundant and widespread rocks in the province. Plate motion is a very unlikely cause for the migrations of felsic activity because of the opposing and orthogonal directions of contemporaneous migration and because geophysical evidence indicates that the Antarctic plate has remained stationary in late Cenozoic time. Fracture propagation is a more likely mechanism, but wedging by forcible injection of magma is difficult to reconcile with an apparent lack of mixing between closely adjacent magma reservoirs. The pronounced space-time patterns of felsic volcanism coupled with the lack of pattern in mafic activity suggest a more complex process. We propose a twostage mechanism in which the rise of mafic magma from the mantle is random in space and time, but passage through the crust has been controlled by a relict system of N-S and E-W fractures that have been systematically reactivated by crustal doming. ¿ American Geophysical Union 1989