THE BAUER SCARP RIDGE JUMP - A COMPLEX TECTONIC SEQUENCE REVEALED IN SATELLITE ALTIMETRY

We investigate here the ridge jump that led to abandonment of the Gala pagos Rise and formation of the Bauer scarp during the initiation of t he present day configuration of the East Pacific Rise since the lower Miocene. We use recently available high resolution satellite-derived g ravity data to investigate in detail the tectonic structure of the eas tern Pacific from the Equator to 20 degrees S. With this data, we iden tify fracture zones, abandoned spreading ridges, scarps, and other sea floor features that provide evidence for discerning tectonic history. Based on our structural interpretation of the satellite-derived gravit y field, we make the following conclusions: (1) The Galapagos Rise spr eading center appears to have originated by opening of the Marquesas/M endana transform complex as a result of the change in spreading direct ion following breakup of the Farallon Plate. (2) The Galapagos Rise wa s not the sole locus of spreading following plate reorganization at si milar to 20 Ma through to the initiation of the Bauer scarp at similar to 8 Ma, as had been previously hypothesized. Rather, it and a second western spreading axis were likely active concurrently, forming a cou nterclockwise-rotating Bauer Microplate at a much earlier stage than t hought previously. (3) The Bauer scarps are pseudofaults associated wi th northward rift propagation. Propagation proceeded in several stages . A first propagator emanating from the Garrett transform complex stal led at the future location of the Wilkes transform creating an area of complex morphology near its northern tip. A second propagator, also e manating from the Garrett complex followed in the first's wake and bro ke through the complex region. At this point the propagation proceeded very rapidly to the northern end of the Bauer Microplate (the Gallego fracture zone, later to become the Yaquina transform fault). Ridge pr opagation continued north in two more stages, creating the Gofar and Q uebrada transforms at the terminus of each stage.