Evidence of transpression along the Clipperton Transform: Implications for processes of plate boundary reorganization

Abstract

High-resolution bathymetry data of the Clipperton Fracture Zone and focal mechanisms of recent earthquakes along the active transform provide evidence for recent and ongoing transpression along the Clipperton Transform. Structural and morphological features observed in the bathymetry data include: normal and strike-slip faults oriented obliquely to the strike of the transform; curved trends of abyssal hills produced by simple shear of the lithosphere bordering the transform fault; abyssal hills offset by obliquely trending strike-slip faults on lithosphere bordering the transform; and lithospheric flexure and associated volcanism near the active transform. All of these features can be explained by a transpression scenario in which a counter-clockwise change in spreading direction of ∼ 5° began about 0.4–0.5 Ma and subjected the right-stepping Clipperton Transform to compression. A comparison of the median ridge volume to calculated estimates of the convergent volume predicted by the transpression scenario indicates that the median ridge is likely to be a product of the brittle deformation associated with transpression. The convergent volume estimates suggest that larger spreading direction changes (∼ 5°) do not occur instantaneously. Instead, spreading direction changes begin slowly and accelerate to the new spreading direction once compression across the transform has ceased. Many of the structures observed along the Clipperton Transform are very similar to features observed along other known convergent transforms, such as the San Andreas Fault in California, and may have important implications for understanding continental transforms. The transpression scenario also indicates that transforms are very important in constraining the rate and character of global plate motion changes.