The amount and quality of observational data available for kinematic studies increased dramatically during the 1980s and 1990s, due in part to the widespread use of bathymetric and side-scan sonar swath-mapping technologies for seafloor surveys. Because the vigor of research into plate motions has historically been driven by access to such data, the contributions of recent marine geophysical measurements to kinematic research are discussed here.
Multi-beam studies of spreading centers have documented the widespread occurrence of discontinuities in axial rises and valleys, ranging from several hundred meter offsets of the spreading axis (DEVALS or deviations from axial linearity) to multi-hundred km long offsets (transform faults) [ Macdonald et al., 1991]. Non-transform discontinuities, which occur along both slow and fast spreading centers [e.g. Grindlay et al., 1992; Carbotte and Macdonald, 1992], often leave ``wakes'' analogous to pseudofaults that disrupt both the seafloor fabric and magnetic lineations flanking the ridge. Wilson [1993b] and Weiland et al. [1993] demonstrate that if dense, well-navigated kinematic data are used to solve for recent plate motions, seafloor deformations as small as a few km (such as that observed in the seafloor fabric near overlapping rift tips) can be detected. If this level of resolution can be extended to time intervals longer than a few Myr, plate reconstructions could become a powerful tool for studying the intraplate rigidity of oceanic lithosphere over long time intervals.
Recent work (e.g. Lonsdale [1994]) demonstrates that rapid reorientation (e.g. less than
10
years)
of spreading axes and transform faults occurs in response to changes in plate directions.
The nearly continuous record of Mesozoic and Cenozoic spreading directions recorded in seafloor
created at ridges has gone largely unexploited due to the lack of modern seafloor surveys located
remote from spreading centers. Fortunately, an increasing number of swath-mapping surveys are now
venturing away from the ridge, and early results are promising. Lonsdale [1991] demonstrates that
isolated swath-mapping profiles constrain the complex kinematic histories of oceanic microplates off
Peninsular California, and a multi-beam survey of the Pitman fracture zone between the Campbell
Plateau and continental rise of Marie Byrd Land is yielding important information about the
Cenozoic history of Pacific-Antarctic motion [ Cande et al., 1992]. The amount of useful kinematic
information from the latter survey argues for similarly designed surveys along other fracture zones.