The Australian-Antarctic Discordance is a unique and enigmatic bathymetric and geologic feature of the mid-ocean ridge system whose origin is poorly understood. We propose an integrated geophysical and geochemical program to study the Discordance zone. The combination of a comprehensive geochemical investigation with a SeaMARC II side-scan sonar survey and detailed magnetic and gravity analyses will provide a unique data set which will focus on two problems which are of fundamental significance, both on a global scale and with respect to the nature and origin of the Discordance itself: (1) the geophysical and geochemical nature of the eastern boundary of the Discordance which is one of the most pronounced geochemical and bathymetric discontinuities in the global mid- ocean ridge system, and (2) the interrelationships among axial depth, axial morphology, ridge segmentation, and along axis petrologic variations, all of which are unusually variable, both within and outside the Discordance. %%% Secondary objectives include the nature of the anomalous, rough topography within the Discordance, the morphotectonic signature of the propagating rifts presently converging toward the Discordance, the geochemical effects of ridge propagation in a region remote form hotspots, the relationship between abyssal lava compositions and high amplitude magnetic anomalies, possible ridge segmentation related major crustal thickness variation within the Discordance, and the possibility of subaxial flow of magma or asthenosphere towards (and into?) the Discordance
