Massive serpentinite carbonation at Linnajavri, N–Norway

Terra Nova, 24, 446–455, 2012 Abstract Carbonation of ultramafic rocks is being considered as an in situ disposal strategy for anthropogenic CO2. We present observations from massively carbonated serpentinites at Linnajavri, N–Norway, where serpentinized fragments of the dismembered ophiolite are hydrothermally altered to soapstone and listvenite on a km‐scale. Several sharp reaction fronts between the soapstone and the serpentinite can be followed for hundreds of metres. Listvenite is present between the underlying carbonate–mica schist and the soapstone. The O‐isotopic compositions of vein minerals in the listvenite and adjacent soapstone indicate an isothermal formation at ∼275 °C. In agreement with C‐isotope signatures, field observations suggest that fluids were derived from overthrusted sediments. Porosimetry data, mass–balance calculations and the perpetuation of serpentinite structures imply an isovolumetric alteration. We conclude that the reactions stopped due to the cessation of the external CO2 supply. Soapstone formation is associated with sequestration of more than 13 Mt of CO2.