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What is the relative rate of movement of the South American, Nazca, Antarctic, African, and Pacific plates?
Actual rates for relative plate velocities have been calculated by several different methods. These attempts use such things as sediment accumulation on the seafloor relative to distance from a spreading axis, the ages of rock formed above a mantle plume (like the Hawaiian Island / Emperor Seamount chain), the ages of magnetic field reversals as recorded in seafloor basalt, and, more recently, satellite laser ranging techniques.
The results of these investigations indicate that the earth's crustal plates are moving at various rates, ranging from a low of approximately 2 centimeters per year in the southeast Africa / Indian Ocean area, to over 15 centimeters per year along the East Pacific Rise west of South America.
With regard to your specific areas, the following values can be used (all are approximate and subject to revision) (source: Physical Geology, by Monroe and Wicander, fig. 12-22):
South American plate: moving relatively westward at 10 cm/year
Nazca plate: moving relatively eastward at 15 to 17 cm/year
Note: this results in a closing velocity of approx. 26 cm/year (approx. 10 inches) where the S.A. and Nazca plates interact. This may help explain the incredible tectonic activity (earthquakes and volcanoes) along the west coast of South America.
Antarctic plate: very confusing, but seems to be moving generally away from the eastern hemisphere (Indian-Australian and Pacific plates) at 5 to 9 cm/year, with additional spreading from South America and the south Atlantic at 1.5 to 2 cm/year
African plate: a real mess! The continent is bounded by spreading on three sides (compression to the north in the Mediterranean Sea), with additional rifting taking place within the plate itself. Fortunately, all of the rates appear to be relatively low, ranging from 1.5 to 2 cm/year in the south and east, to 2.5 to 5 cm/year where it is moving eastward from the Mid-Atlantic Ridge.
Pacific plate: again highly variable, but in general moving west-northwest at speeds ranging from 10 to 18 cm/year along the East Pacific Rise, to 4 to 10 cm/year where it runs into Australia and Asia.
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