Episodic circulation of reactive fluids along faults - From travertine- to basin-scale study on the Colorado Plateau natural example (USA)
Episodische circulatie van reactieve fluïda langsheen breuken: van travertijn tot bekken schaal studie van het Colorado Plateau voorbeeld (USA)
Frery, Emanuelle; R0221513
Understanding the mechanisms of porosity/permeabilityevolution during fluid circulation episodes in a fault zone is a current challenge. This multidisciplinary study of CO2 natural leakage in the ColoradoPlateau area reveals a localization and several episodes of CO2 fluidscirculation operating along faults .By means of field to thin sectionscale studies, coupling structural geology, petrography, stable isotopes andU/Th geochemistry, we investigated i) the field evidences of CO2-leakage fromdeep horizons toward the surface, ii) the alternating circulation and sealingprocesses, iii) the spatial evolution of the CO2 leakages and of thecomposition of the fluids, and finally iv) the overall fluid circulationhistory by dating the diagenetic cements and travertines.Fieldwork across a fractured zone alllowedto reconstruct the architecture of the CO2 path from the depth to the surface.The CO2 leaking zone migrated spatially and temporally along the faults: tracesof fossil and modern leakages are obvious at fault relay zones with amineralization concentration reaching an average thickness up to 15 meters atground level, mainly expressed by calcium carbonate veins and surfacetravertine. Dedicated petrographic and geochemical studies of this zone revealedsuccessive episodes of dissolution and precipitation. The precipitation couldtake place after the opening of dissolution cavities or the two dissolution andprecipitation processes could operate at the same time, depending on both thefluid flow and the pore fluid pressure. The joint study of stable isotopes andU/Th dating of representative samples ranging from late Pleistocene untilpresent day and collected at a same leaking place allows also to calibrate theCO2 leakage time-laps, rates, cycles and volumes and to discuss this archivemeaning. Based on these results, we propose a conceptual andnumerical modeling of CO2-leakage through a faulted zone which links episodicvariations of CO2-circulation to successive stages of fault opening andsealing: CO2-input corresponding to the opening of the fault is followed by anexponential decrease rate of the CO2 flowrelated to the post-seismic fault sealing by the mineralization of calciumcarbonate.