Assessing hydrological controls on the lithium isotope weathering tracer

Pogge von Strandmann, Philip A.E., Cosford, Lara R., Liu, Chun Yao, Liu, Xianyi, Krause, Alexander J., Wilson, David J., He, Xiaoqing, McCoy-West, Alex J., Gislason, Sigurður R., and Burton, Kevin W. (2023) Assessing hydrological controls on the lithium isotope weathering tracer. Chemical Geology, 642. 121801.

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To investigate the impact of riverine discharge and weathering intensity on lithium isotopes (δ7Li) in a mono-lithological terrain, this study examines the dissolved load and leached suspended load (exchangeable, oxide, and clay fractions) from Icelandic rivers spanning a wide range of discharge, weathering rates, and weathering intensity. The δ7Lidissolved co-varies inversely with the discharge, confirming that water-rock interaction time is a primary control on the secondary mineral formation that fractionates Li isotopes. The “boomerang” shape observed in global rivers between the weathering intensity (i.e. W/D = weathering rate/denudation rate) and δ7Lidissolved also exists for these basaltic rivers at low to medium W/D. However, these rivers do not extend to such low δ7Lidissolved values as seen in the global compilation at low W/D, indicating that there is a lithological control on this relationship arising from the type of the lithology-specific secondary minerals forming and their precipitation rates. In addition, the Δ7Lix-dissolved between each leached solid phase and the dissolved load also co-varies with discharge. At low discharge (long water-rock interaction times), Δ7Lix-dissolved values agree with experimentally-determined equilibrium values, whereas less fractionated values are observed at higher discharge (shorter water-rock interaction times). As a result, there is a different relationship between W/D and Δ7Liclay-source in this basaltic terrain than previously reported from global multi-lithological river sediment samples, with clay leachates from Iceland more closely mimicking the boomerang shape of the dissolved load. However, the relationship between δ7Li and weathering processes is complicated because the fractionation between the clay fraction and the dissolved load is not constant but varies with both W/D and discharge. Overall, this study confirms the utility of Li isotopes as a tracer of modern and palaeo-weathering processes, and also has important implications for the specific interpretations of detrital δ7Li values, which may be more sensitive to weathering parameters than previously thought.

Item ID: 81046
Item Type: Article (Research - C1)
ISSN: 1872-6836
Keywords: Basalt weathering, Clay formation, Secondary mineral formation, Silicate weathering, Weathering intensity
Copyright Information: © 2023 Elsevier B.V. All rights reserved
Date Deposited: 21 Nov 2023 03:01
FoR Codes: 37 EARTH SCIENCES > 3709 Physical geography and environmental geoscience > 370901 Geomorphology and earth surface processes @ 50%
37 EARTH SCIENCES > 3703 Geochemistry > 370303 Isotope geochemistry @ 50%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280111 Expanding knowledge in the environmental sciences @ 40%
28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 60%
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