Serpentinization rates measured in olivine micro-reactors
Abstract
Few experimental studies have determined the rates of serpentinization of olivine, and reported rates are widely divergent. Here we present the results of a novel experimental approach developed to constrain serpentinization rates in situ by using synthetic fluid inclusions (SFI) as micro-reactors. We assessed the effect of fluid compositions and salinity on reaction pathways and dissolution kinetics for serpentinization of olivine (Fo85) at 280°C. To this end, we used three distinct fluids, including H2O-NaCl, H2O-MgCl2 and H2O-NaCl-MgCl2, with salinities of 1, 3.5, 6 and 10 wt.% . Raman, SEM and TEM analyses indicate that brucite and serpentine formed only after a few days, whereas magnetite was only observed in the experiments that lasted longer than 120 days. As a result of the limited solubility of Na and Cl in serpentine and brucite the salinity increased in our experiments as serpentinization progressed. Salinity changes were monitored by changes in the freezing-point depression and the calculated amounts of H2O consumed during the precipitation of serpentine and brucite were used as a proxy for reaction progress. The olivine micro-reactor experiments revealed that the serpentinization rates are strongly sensitive to the salinity and composition of the fluid. Our results indicate a rapid decrease in reaction rates with increasing salinity. The calculated average rates for salinities of 1 wt.% and 3.5 wt.% are 6.73 x 10-9 (mol/m2sec) and 2.91x 10-9 (mols/m2sec), respectively, whereas for the 6 and 10 wt.% starting compositions the rates were 8.39 x 10-10 (mol/m2sec) and 7.12 x 10-11 (mol/m2sec), respectively. The 0.1 log units scatter in the measured rates (Fig. 1A) is similar to variations in rates determined using other methods (Rimstidt et al., 2012). The serpentinization rates obtained with the micro reactors overlap with recent experimental studies (Malvoisin et al., 2012; McCollom et al., 2016), but are several orders of magnitude slower than values obtained in older experimental studies (Fig. 1B). Current work is being conducted to extend the range of conditions to different temperatures, adding CO2 to the system, and examining the effect of olivine composition (Mg/Fe).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.B33I..01L
- Keywords:
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- 0450 Hydrothermal systems;
- BIOGEOSCIENCESDE: 0456 Life in extreme environments;
- BIOGEOSCIENCESDE: 1038 Mantle processes;
- GEOCHEMISTRYDE: 1039 Alteration and weathering processes;
- GEOCHEMISTRY