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Self diffusion of europium, neodymium, thorium, and uranium in haplobasaltic melt: The effect of oxygen fugacity and the relationship to melt structure

LaTourrette, T. and Wasserburg, G. J. (1997) Self diffusion of europium, neodymium, thorium, and uranium in haplobasaltic melt: The effect of oxygen fugacity and the relationship to melt structure. Geochimica et Cosmochimica Acta, 61 (4). pp. 755-764. ISSN 0016-7037. doi:10.1016/S0016-7037(96)00377-8.

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We report new measurements of self diffusion coefficients (D) for Mg, Nd, Eu, Th, and U in a haplobasaltic (Fo_(15)Di_(40)An_(45)) melt at 1 atm, 1400–1500°C, and oxygen fugacities corresponding to air and the Fe-FeO buffer. Diffusion couples consisted of isotopically distinct melts of the same chemical composition, and isotopic concentration profiles in quenched couples were measured with an ion probe. The valence state distributions of Eu and U were determined from absorption spectroscopy and model calculations, which demonstrate a shift from Eu^(3+) and U^(5.5+) in air to Eu^(2.5+) and U^(4+) at Fe-FeO. D_(Mg), D_(Nd), and D_(Th) are independent of oxygen fugacity and agree well with our previous measurements. D_(Eu) = D_(Nd) in air and increases by 42% at Fe-FeO, while D_U = D_(Th) in air and shows a possible small increase of ∼20% at Fe-FeO. The change in D_(Eu) with oxygen fugacity matches the established ionic radius and charge dependence for Mg, Ca, Ba, Nd, Yb, Ti, and Zr, while diffusion coefficients for Zr, Th, U^(4+), and U^(5.5+) are independent of ionic radius and charge. Activation energies for all cations are approximately equal, independent of oxygen fugacity, and approximately match the activation energy for viscous flow. In addition, activation energies and diffusion coefficients recently measured for O and Si in basalt agree well with the present values. The good agreement between the various activation energies and between network modifier and network former diffusivities is consistent with a model in which diffusion of network modifying cations in low viscosity melts is controlled largely by the extrinsic influence of the melt network reorganization, with an additional influence from the intrinsic mobilities of the individual cations. The constant diffusion coefficient defined by the high ionic radius and charge elements is interpreted to represent the characteristic network diffusivity for this composition, which dominates over the intrinsic diffusivities for these elements. Elements with faster intrinsic diffusivities still display a small ionic radius and charge dependence. Diffusion coefficients in high viscosity melts are expected to be decoupled from the network, and thus may display a much greater dependence on ionic radius and charge.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1997 Elsevier Science Ltd. Received May 30, 1996; accepted in revised form November 3, 1996. We gratefully acknowledge G. Rossman for his kindness in making his spectroscopic laboratories available to us and in assisting with the measurements. We also benefited from helpful discussions with G. Huss, expert technical assistance from M. Heinrich and P. Carpenter, and thorough reviews by D. Baker and T. Dunn. D. Burnett kindly allowed us to use his sample preparation facilities, hopefully preventing the discovery of any spectacular isotopic anomalies by our co-workers. This work was supported by DOE grant DE-FG-03-88ER-13851. Caltech contribution 5680(935). Editorial handling: D. B. Dingwell.
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Department of Energy (DOE)DE-FG-03-88ER-13851
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Caltech Division of Geological and Planetary Sciences5680
Lunatic Asylum Lab935
Issue or Number:4
Record Number:CaltechAUTHORS:20131119-095721373
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Official Citation:T. la Tourrette, G.J. Wasserburg, Self diffusion of europium, neodymium, thorium, and uranium in haplobasaltic melt: The effect of oxygen fugacity and the relationship to melt structure, Geochimica et Cosmochimica Acta, Volume 61, Issue 4, February 1997, Pages 755-764, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42560
Deposited By: Ruth Sustaita
Deposited On:19 Nov 2013 18:13
Last Modified:10 Nov 2021 16:25

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