The stable calcium isotopic composition of rivers draining basaltic catchments in Iceland

• Published in: Earth and Planetary Science Letters
• Main Authors: Hindshaw, Ruth, Bourdon, Bernard, Pogge von Strandmann, Philip A.E., Vigier, Nathalie, Burton, Kevin
• Other Authors: Institute of Geochemistry and Petrology ETH Zürich, Department of Earth Sciences Swiss Federal Institute of Technology - ETH Zürich (D-ERDW), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich)-Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Department of Earth Sciences Oxford, University of Oxford, Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Department of Earth Sciences Durham, Durham University
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2013
• Subjects: calcium; calcium isotopes; Iceland; chemical weathering; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences
• Online Access: https://hal.univ-lorraine.fr/hal-01764530; https://doi.org/10.1016/j.epsl.2013.05.038

International audience Calcium isotopic compositions () were measured in Icelandic rivers draining a range of catchment types. The values of the rivers ranged from 0.45‰ to 0.67‰, which in all cases was higher than the value of basaltic rock standards (0.42±0.03‰). A single explanation was unable to satisfactorily explain the values of all rivers, rather it was found that the rivers formed three distinct groups based on the extent of glacial coverage in each catchment. The Ca isotopic composition of rivers draining catchments with less than 10% glacial cover could be explained by the mixing of water sources: basalt-derived solutes, meltwater (taken to represent meteorological precipitation inputs) and hydrothermal water. However, fractionation of in these catchments cannot unequivocally be ruled out. In catchments with greater than 22% glacial cover, Ca isotopic compositions could not be explained by a mixture of water sources and instead reflected a fractionation process, most likely the precipitation of Ca-bearing secondary minerals or the adsorption/ion-exchange of Ca onto mineral surfaces. The fractionation factor () for this process was calculated to be 0.9999. The third group of rivers, with partially glaciated (10–21%) catchments, grouped with glaciated catchments with respect to their Sr geochemistry and with non-glaciated catchments with respect to their Ca geochemistry. The difference in the controls of Ca isotope fractionation between glaciated and unglaciated catchments was attributed to different weathering regimes.