Positive correlation between Li and Mg isotope ratios in the river waters of the Mackenzie Basin challenges the interpretation of apparent isotopic fractionation during weathering

Tipper, E. T. and Calmels, D. and Gaillardet, J. and Louvat, P. and Capmas, F. and Dubacq, B. (2012) Positive correlation between Li and Mg isotope ratios in the river waters of the Mackenzie Basin challenges the interpretation of apparent isotopic fractionation during weathering. Earth and Planetary Science Letters, 333–33. pp. 35-45. ISSN 0012-821X DOI 10.1016/j.epsl.2012.04.023

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Abstract

During chemical weathering, magnesium (Mg) is released by the dissolution of both carbonate and silicate sources. The degree to which solute concentrations and isotopic compositions of rivers reflect the relative proportions of these two inputs, or cycling by a series of processes associated with weathering is poorly constrained. In the river waters of the Mackenzie Basin (Canada), the Mg content is high and Mg isotope ratios (26Mg/24Mg expressed as δ Mg 26 ) show in excess of one per mil variability. Part of this variability is attributed to the 3‰ range in the carbonate and silicate rocks drained. Despite this inherent lithological control on river water δ Mg 26 values, there is also evidence for a fractionation control. A linear positive covariation between lithium (7Li/6Li, expressed as δ Li 7 ) and Mg isotope ratios in the river waters of the Mackenzie Basin is reported. This covariation is not expected because previously reported fractionation related to physicochemical processes associated with clays or oxides should induce a negative covariation with Mg isotope ratios.

Item Type: Article
Uncontrolled Keywords: 2012AREP; IA63;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 333–33
Page Range: pp. 35-45
Identification Number: 10.1016/j.epsl.2012.04.023
Depositing User: Sarah Humbert
Date Deposited: 27 Jun 2012 14:45
Last Modified: 23 Jul 2013 10:04
URI: http://eprints.esc.cam.ac.uk/id/eprint/2550

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