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Natural Serpentinite Carbonation at Linnajavri, N-Norway (Invited)

Control ID: 1789821

Title: Natural Serpentinite Carbonation at Linnajavri, N-Norway (Invited)

Authors (First Name, Last Name): Andreas Beinlich1, 7, Masako Tominaga2, Oliver Pluemper3, Joern Hoevelmann4, Maurice Tivey5, Eduardo Andrade Lima6, Benjamin P Weiss6, HÃ¥kon Austrheim7, Bjorn Jamtveit7

Institutions (All):

  1. Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada.
  2. Department of Geological Sciences, Michigan State University, East Lansing, MI, United States.
  3. Department of Earth Sciences, Utrecht University, Utrecht, Netherlands.
  4. Institut für Mineralogie, University of Münster, Münster, Germany.
  5. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, United States.
  6. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States.
  7. Physics of Geological Processes, University of Oslo, Oslo, Norway.

Abstract Body: Investigation of natural mafic and ultramafic rock carbonation driven by the infiltration of CO2-bearing fluids into a solid rock unit provides insight into feedback mechanisms that may become important for in situ sequestration schemes of anthropogenic CO2. We present observations from massively carbonated serpentinites at Linnajavri, N–Norway, where completely serpentinized fragments of the dismembered ophiolite are hydrothermally altered on a km–scale to ophicarbonate (serpentine + Mg-carbonate), soapstone (talc + Mg-carbonate) and listvenite (quartz + Mg-carbonate). Field observations indicate that tectonic preprocessing of the serpentinite facilitated fluid infiltration. Listvenite is indicative of the most intense carbonation and is present along the tectonic contact of the ophiolite with the underlying carbonate-mica schist. Soapstone/steatite is indicative of less intense carbonation, forms m-wide reaction halos around fractures within the serpentinite and is also present as massive body between the listvenite and unaltered serpentinite. Sharp reaction interfaces between the soapstone and serpentinite can be traced for several hundred meters and are defined by the breakdown of antigorite to form magnesite and talc. The soapstone-listvenite transition zones are not entirely exposed in the field and are less than 5 m wide. 18O thermometry using the isotopic composition of quartz/talc and coexisting magnesite derived from veins and bulk rock samples indicate an isothermal formation of listvenite and soapstone at ~275°C. The corresponding isotopic signature of the fluid (δ13CVPDB = 2.2(5) ‰) derived from the δ13C composition of magnesite suggests an interaction with crustal rocks and devolatilization of associated overthrusted sediments as a possible source for the CO2. He- and Hg-porosimetry data, mass–balance calculations, and the preservation of serpentinite structures imply an isovolumetric alteration, which indicates that the carbonation declined due to the cessation of externally supplied CO2. The presence of sharp alteration fronts implies that reaction rates were fast relative to CO2 transport rates. Carbonation at Linnajavri was accompanied by partial dissolution of (Cr)-magnetite and incorporation of the released Fe in precipitating carbonate minerals. SQUID microscopy mapping of both natural remanence magnetization (NRM) and anhysteretic remanence magnetization (ARM) confirms different bulk intensities for the serpentinite, soapstone and listvenite samples. The alteration dependent distribution of ferromagnetic minerals suggests that magnetic surface mapping may represent a powerful tool to localize the position of reaction fronts between pristine and carbonated rock types and hence the spatial extent of the carbonation progress.

Keywords: 3616 MINERALOGY AND PETROLOGY Hydrothermal systems, 3617 MINERALOGY AND PETROLOGY Alteration and weathering processes, 3625 MINERALOGY AND PETROLOGY Petrography, microstructures, and textures.