GEOLOGY: Maintaining the Spread

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Science  23 Aug 2002:
Vol. 297, Issue 5585, pp. 1239e-1241e
DOI: 10.1126/science.297.5585.1239e

Seafloor is created at mid-ocean spreading ridges and is consumed (back into Earth's mantle) at subduction zones. The age of the ocean floor increases away from ridges, and crust from 180 million years ago (Ma) is still exposed in the western Pacific Ocean. The rate of creation reflects heat loss from the mantle, and some estimates have indicated that recent spreading rates have varied by as much as 50%. Using recent syntheses of past plate geometries and data on the area of ocean crust as a function of age, Rowley shows that the rate of production of new seafloor has remained relatively constant (3.4 km2/year) during the past 180 million years. This period includes times when the geometry of ocean spreading ridges changed greatly (about 40 Ma) and when large oceanic volcanic provinces were formed (about 100 Ma). A constant mid-ocean ridge production rate also implies that the mean depth of the oceans has been constant during this period. — BH

Geol. Soc. Am. Bull. 114, 927 (2002).

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