Distributed Extension at the Galapagos Triple Junction, Eastern Equatorial Pacific

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OCE-0751831Intellectual Merit: The overall goals of this work are to understand how deformation is distributed at tectonic plate triple junctions, in general, and to elucidate the kinematic evolution of the Galapagos triple junction, in particular. The research program includes a 5-day multibeam bathymetry survey and concurrent magnetometer survey at the Galapagos triple junction, a ridge-ridge-ridge (RRR) triple junction where the Cocos, Nazca, and Pacific plates meet, separated by the Galapagos microplate. The specific goals are to 1) determine whether the stresses associated with the propagating Cocos-Nazca (C-N) Rift control the location and stability of rifting of the lithosphere to its north and south and, 2) understand what conditions might have led to the stabilization of the southern RRR triple junction at Dietz Deep Rift and the subsequent development of the rotating Galapagos microplate. A secondary goal is to place additional constraints on the rotation rate of the Galapagos microplate, which is still a matter of debate. North of the C-N Rift there has been a succession of transient rifts and triple junctions with the EPR. A simple crack interaction model predicts that the locations of these northern rifts are controlled by the distance of the tip of the C-N Rift to the EPR. The model also predicts that tensile stresses should be symmetrical about the Rift, and thus, transient rifts could occur south of the C-N Rift. Currently, this is not the case: to the south the Galapagos microplate has been stable for ~1 My. No data have been collected along the trace of the southern triple junction prior to the formation of the microplate, however, to assess whether there was a symmetrical occurrence of multiple jumping rifts then. Nor do we have sufficient data to understand the conditions that favored the development, stabilization and growth of Dietz Deep Rift and led to the formation of the rotating Galapagos microplate. To test the applicability of the crack interaction model, large gaps in the multibeam bathymetry data along the Dietz Deep Rift will be filled, and for the first time the trace of the predicted southern triple junctions out to ~5 My will be mapped. These data will help to answer several outstanding questions about the kinematics of the Galapagos triple junction region and the response of the lithosphere to stress. The results should be applicable to other oceanic triple junctions and applicable to mid-ocean ridges where microplates are forming and have formed in the past. As such this research program will fill in important gaps in our understanding of fundamental processes of plate tectonics and of the evolution of the Earth's oceanic crust.Broader Impacts: This project includes training of a Ph.D. student both at sea and on shore. The Principal Investigator hosts high school students at WHOI every year to introduce students to researchers, new theories and data. The data that will be collected will be ideal for presentations and discussions with the students. The cruise report will be made available immediately upon return from the cruise; and he processed bathymetry, sidescan, and magnetic data as well as any derived products will be made available immediately, to the wider scientific community and public. The raw multibeam data will be sent to the Ridge 2000 multibeam synthesis site as part of their general bathymetric database. Finally, WHOI has agreed to contribute funds to cover the costs of producing animations of the evolution of the Galapagos triple junction region. The models that will be developed are hard to conceptualize, especially for students and the general public. Animations will aid tremendously in describing and disseminating the results of this work.