Evolution of the Bauer Microplate, Eastern Tropical Pacific

Bauer microplate structural patterns revealed by a 1997 partial multibeam survey of the Galapagos Rise, and a 2000 survey of the northern microplate boundary, in conjunction with archived bathymetric, magnetic and gravimetric data, allow for a fairly detailed interpretation of the fossil plate's tectonic history, and illustrate some of the important factors influencing its evolution. We recognize four phases in the protracted and complex evolution of the microplate; (1) formation, (2) fast-rotation, (3) slow-rotation, and (4) capture. The microplate formed at approximately 17 Ma along the Pacific-Nazca accreting plate boundary following initial northward rifting from a long, right-stepping transform (Mendana descendant) with growth primarily through ridge propagation. At about 15 Ma the microplate began a prolonged period of stable, accretionary growth, with compression along the northern boundary and the opening of a deep comparable to Pito and Endeavor (forming part of Bauer Scarp and its conjugate Anti-Bauer Scarp). The two earliest stages were dominated by spinning driven by its bounding plates (Pacific and Nazca) with accretion of lithosphere along its eastern and western margins (the Galapagos Rise and East Pacific Rise spreading axes, respectively). A linking transform (Woce) was established along the southern microplate boundary at 10 Ma, decreasing Bauer-Nazca shear couple and dramatically reducing microplate spinning. Concomitant northward propagation of the EPR axis appended a large section of the Pacific plate to the Bauer microplate's northern boundary. The microplate was captured by the Nazca plate at 5.8 Ma after Quebrada transform formation linked the propagating EPR axis and the overlapped axis to the east. Comparisons are made with active rise-crest microplates (Easter and Juan Fernandez) and the edge-driven kinematic model of Schouten and others. The role of microplate-bounding transforms, which impact microplate kinematics, are also investigated. Lessons learned from Bauer capture are tentatively applied to the Easter and Juan Fernandez plates.