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Experimental determination of exchange mechanism and hydrogen isotope fractionation between chlorite and water

English title Experimental determination of exchange mechanism and hydrogen isotope fractionation between chlorite and water
Applicant Vennemann Torsten
Number 116550
Funding scheme Project funding (Div. I-III)
Research institution Institut de Minéralogie et Géochimie Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Geochemistry
Start/End 01.04.2007 - 31.03.2009
Approved amount 156'994.00
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Keywords (8)

Isotope geochemistry; Hydrogen; Equilibrium fractionations; Chlorite; Experiments; Isotope; Fractionation; Geochemistry

Lay Summary (English)

Lay summary
Chlorite is a common hydrous mineral in the Earth’s crust and is important for petrologic and geochemical studies, most notably for studies on fluid-rock interactions during metamorphic or igneous processes. The stable hydrogen isotope composition of chlorite can be used to determine the hydrogen isotope composition of water, which is a proxy for studying the origin of fluids. However, at low temperatures the hydrogen isotope fractionations between chlorite and water at equilibrium conditions have not been experimentally determined. Experiments, conducted under controlled conditions, provide the basis for understanding the fractionations between mineral and fluid phases and can subsequently be applied to studies of natural samples. In this study, low temperature experiments based on the hydrogen isotope exchange between molecular hydrogen and chlorite are conducted in order to obtain such equilibrium fractionation factors. At temperatures between 200 and 300°C the experiments suggest that the differences in hydrogen isotope composition between Mg-chlorite and water are between 0 and 70 per mil. Experiments at temperatures between 300 and 400°C give larger differences of about 200 per mil; much lower than those previously estimated from higher temperature experiments (higher than 500°C) and calibrations based on natural samples from geothermal areas at temperatures between 110 and 350°C. Calculations using shifts of atomic vibrations when hydrogen is substituted by deuterium in the mineral structure give results comparable to extrapolations from higher temperature experiments done previously, but indicate that the fractionation factor may increase sharply at temperatures lower than 100°C. The experimental fractionation factors obtained so far may change the interpretation of fluid sources obtained from measured isotopic compositions of natural chlorites.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
102014 Controls on mineral-fluid oxygen and hydrogen isotope fractionations in specific geologic systems 01.10.2003 Project funding (Div. I-III)
143885 Origin and growth of Alpine fissure minerals: fluid-mineral interaction and implications for the Alpine metamorphism 01.10.2012 Project funding (Div. I-III)
140498 Chlorite as a key mineral for geothermometry: Empirical verifications of thermodynamic models for Fe-Mg aluminous chlorite and calibration of the oxygen isotope fractionation between chlorite, quartz and calcite 01.05.2012 Project funding (Div. I-III)