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Science 19 January 2007:
Vol. 315. no. 5810, p. 297
DOI: 10.1126/science.315.5810.297g
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Plate tectonics assumes that rigid plates float and move over the weaker asthenosphere, which extends from about 60 to 220 kilometers below the oceans and 150 kilometers below continents. The softness of the asthenosphere may be caused by pockets of hydrous melt. Mierdel et al. (p. 364; see the Perspective by Bolfan-Casanova) have performed experiments which show that the asthenosphere could coincide with a zone that marks a minimum in the solubility of water in mantle minerals. A sharp drop occurs in water solubility in aluminous orthopyroxene with pressure, or equivalently depth, whereas the water solubility in olivine continuously increases. The limits of the asthenosphere would be the regions where water comes out of solution and forms pockets of hydrous silicate melt.




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