Plate Kinematics of the South Atlantic: Chron C34 to Present

摘要

A high-resolution seafloor spreading history of the South Atlantic Ocean since chron C34 is constrained by a combination of Seasat altimeter data and underway marine geophysical data. A set of 45 finite rotation poles defines the relative position of Africa and South America at roughly 2-m.y. intervals. A set of 12 stage poles constrain the relative motion of these two plates at 5- to 10-m.y. intervals. The position of the stage poles continuously migrates, reflecting the continuously changing azimuths of the fracture zones. Major changes in spreading direction are observed in the Late Cretaceous and early Cenozoic as the fracture zones sweep out broad S-shaped curves similar to the pattern seen on the Kane fracture zone in the central Atlantic. Small offset fracture zones were found to be the most accurate recorders of changes in plate motion. A comparison of synthetic fracture zones are based on the South Atlantic stage poles to the observed trends of fracture zones in the equatorial Atlantic indicates that the Vema and Marathon fracture zones were generated by South Atlantic spreading, as opposed to central Atlantic spreading, at least as far back as 35 m.y. ago and possibly 50 m.y. ago. Reprints. (edc)