Cracking of lithosphere north of the Galapagos triple junction

Abstract

The Galapagos triple junction is a ridge-ridge-ridge triple junction where the Cocos, Nazca, and Pacific plates meet around the Galapagos microplate. Directly north of the large scarps of the Cocos-Nazca Rift, a 250-km-long and 50-km-wide band of northwest-southeast–trending cracks with volcanics at their western ends crosscuts and blankets the north-south–trending abyssal hills of the East Pacific Rise. It appears that the roughly northeast-southwest extension of East Pacific Rise–generated seafloor has been accommodated by a succession of minor rifts that, during at least the past 4 m.y., had their triple junctions with the East Pacific Rise at distances of 50–100 km north of the tip of the propagating Cocos-Nazca Rift. We propose that the rift locations are controlled by stresses associated with the dominant Cocos-Nazca Rift, and scaled by the distance of its tip to the East Pacific Rise. We speculate that similar ephemeral rifts occurred south of the Cocos-Nazca Rift and were instrumental in the origin of the rotating Galapagos microplate ca. 1.5 Ma.