At the Galapagos triple junction, the westward propagating Cocos?Nazca (C?N) Rift breaks into ~0.5 Ma crust accreted at the East Pacific Rise. Rifting transitions to full magmatic seafloor spreading in the wake of the propagating tip. The 25?km?long Hess Deep rift is the transitional segment from rifting to spreading. Intrarift ridge (IRR), located within Hess Deep rift, is interpreted as a detachment fault, which exhumes deep?seated rocks to the seafloor. Although transitional segments must have occurred throughout the westward propagation of C?N Rift, IRR is the only obvious detachment fault along the base of the Rift scarps in the last ~5 Ma of its propagation. IRR formation may be in response to a decrease in spreading rate (~40 to <20 mm/yr) and presumed lower melt supply, resulting from the formation of the Galapagos microplate ~1.4 Ma, which now controls the opening at the C?N Rift tip.