No. 116: Mar-Apr 1998
The earth's tectonic plates are usually drawn as neatly fitting puzzle pieces. This idealistic picture is changing because several lines of evidence suggest that some plates are separated by miles of geological "mush."
J-Y. Royer and R.G. Gordon came to this conclusion after careful inspection of the huge Indo-Australian plate. First, they noticed that many powerful earthquakes originated in the center of this plate. Usually, quakes are confined to the edges of plates where they crunch against neighboring plates. Second, a line of folds 3,000 feet high runs down the center of the plate, as if is being squeezed like an accordion. But they could not identify any geological accordionist. Finally, working backwards in time using paleomagnetic data, they reconstructed plate configurations 11 million years ago. The Indo-Australian plate did not match up with its neighbors of that time period. Royer and Gordon concluded that the Indo-Australian plate really consists of three smaller plates. Even more surprising was their discovery that in between the boundaries of the three new plates there is a tectonic morass perhaps a thousand miles wide in places -- the "miles of mush" of our title.
Plate tectonics (nee "continental drift"), once a revolutionary idea in geology and geophysics, seems poised for another upheaval.
(Anonymous; "Gaps in the Theory," Earth, 7:11, February 1998.)