Isotopic evidence for uranium exchange during low-temperature alteration of oceanic basalt |
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| Authors: | JD MacDougall RC Finkel J Carlson S Krishnaswami |
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| Institution: | Scripps Institution of Oceanography, La Jolla, CA 92093 U.S.A.;Physical Research Laboratory Ahmedabad, 380009 India |
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| Abstract: | Measurements of uranium concentration and the234U/238U activity ratio in oceanic basalts which have undergone low-temperature seafloor alteration indicate that uranium uptake is a pervasive occurrence but that the various phases involved behave differently with respect to this process. Palagonite exhibits uranium contents 8–20 times higher than unaltered glass coupled with low234U/238U, suggesting ongoing preferential leaching of234U. Altered crystalline interiors of several old basalts have234U/238U > 1, indicative of recent uranium exchange with seawater. The data also provide evidence for uranium sources with234U/238U higher than the seawater value of 1.14. Manganese crusts on basalts of a variety of ages have isotopic ratios indicating that they either are recent deposits or also have experienced continuing uranium exchange with seawater. |
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