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Science 28 October 2005:
Vol. 310. no. 5748, pp. 654 - 657
DOI: 10.1126/science.1116349
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Reports

Dating the Growth of Oceanic Crust at a Slow-Spreading Ridge

Joshua J. Schwartz,1 Barbara E. John,1 Michael J. Cheadle,1 Elena A. Miranda,1 Craig B. Grimes,1 Joseph L. Wooden,2 Henry J. B. Dick3

Nineteen uranium-lead zircon ages of lower crustal gabbros from Atlantis Bank, Southwest Indian Ridge, constrain the growth and construction of oceanic crust at this slow-spreading midocean ridge. Approximately 75% of the gabbros accreted within error of the predicted seafloor magnetic age, whereas ~25% are significantly older. These anomalously old samples suggest either spatially varying stochastic intrusion at the ridge axis or, more likely, crystallization of older gabbros at depths of ~5 to 18 kilometers below the base of crust in the cold, axial lithosphere, which were uplifted and intruded by shallow-level magmas during the creation of Atlantis Bank.

1 Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA.
2 U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA.
3 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.

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