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Crustal links record plate motions.

The seafloor has been likened to a giant tape recorder tape recorder, device for recording information on strips of plastic tape (usually polyester) that are coated with fine particles of a magnetic substance, usually an oxide of iron, cobalt, or chromium. The coating is normally held on the tape with a special binder. , because as it is churned out conveyor-belt-style at mid-oceanic ridges, it becomes imprinted with the earth's changing magnetic field. The resultant "magnetic stripes" that line the ocean floor enable scientists to reconstruct the past positions of the continents as they, and the plates upon which they sit, move around the globe.

But these magnetic lines are not the only oceanic record of relative plate motions. REcent studies by Brian E. Tucholke and Hans Schouten at Woods Hole Woods Hole, uninc. village (1990 pop. 1,080) and seaport in the town of Falmouth, Barnstable co., SE Mass., at the southwestern extremity of Cape Cod. It is the departure point for nearby island resorts (Martha's Vineyard, Nantucket).  (Mass.) Oceanographic Institution indicate that the motions are reflected on a much finer scale in the structure of fracture zones that cut across ocean basins, perpendicular to mid-oceanic ridges. While Tucholke and Schouten have focused on one fracture zone, they suspect the structures of all fracture traces are very similar. What's more, the researchers think they see evidence in fracture zone structure for global changes in plate motions every few million years. They presented their findings at the recent meeting of the Geological Society of America The Geological Society of America (or GSA) is a nonprofit organization dedicated to the advancement of the geosciences. The society was founded in New York in 1888 by James Hall, James D.  in Orlando, Fla.

Using seismic reflection and bathymetry ba·thym·e·try  
The measurement of the depth of bodies of water.

 (seafloor depth) data, Tucholke and Schouten examined the detailed structure of two 700-kilometer-long segments situated on each side of the Mid-Atlantic Ridge. The researchers located spots where the fracture zone had changed direction or where it had been blocked -- perhaps by the upwelling up·well·ing  
1. The act or an instance of rising up from or as if from a lower source: an upwelling of emotion.

 of molten rocks at times when changes in plate motion caused the crust near the ridge axis to be stretched out. They found that the kinks and bends on the western segment correlated remarkably well with similar structural changes in the eastern limb.

Tucholke and Schouten also compared a 450-km-long Kane segment straddling strad·dle  
v. strad·dled, strad·dling, strad·dles
a. To stand or sit with a leg on each side of; bestride: straddle a horse.

 the ridge with similar segments in the Pacific and Indian oceans. "There are plate motion changes recorded in all of these oceans at roughly the same times -- at about 4.5 million years, 2.5 million years and 1 million years," says Tucholke. "So what we're seeing at the Kane fracture zone is a global response."

Tucholke expects that more detailed studies will show crustal crust·al  
Of or relating to a crust, especially that of the earth or the moon.

Adj. 1. crustal - of or relating to or characteristic of the crust of the earth or moon
 structure to be an extremely precise indicator of changes in plate motion. But what causes these changes is anyone's guess. "Perhaps the plates move like bumper cars and get hung up every 2 million to 3 million years," says Tucholke. "Where and why this happens is the $64,000 question."
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Author:Weisburd, Stefi
Publication:Science News
Date:Nov 16, 1985
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