Progressive veining during peridotite carbonation: insights from listvenites in Hole BT1B, Samail ophiolite (Oman)

Abstract. The reaction of serpentinized peridotite with CO2-bearing fluids to form listvenite (quartz–carbonate rock) requires massive fluid flux and significant permeability despite an increase in solid volume. Listvenite serpentinite samples from Hole BT1B the Oman Drilling Project help understand mechanisms feedbacks during vein formation this process. Samples analyzed study contain abundant magnesite veins closely spaced, parallel sets younger quartz-rich veins. Cross-cutting relationships suggest that antitaxial, zoned elongated grains growing a median zone towards wall rock are among earliest structures carbonation serpentinite. Their bisymmetric chemical zoning variable Ca Fe contents, systematic distribution SiO2 Fe-oxide inclusions these zones, cross-cutting relations oxides Cr spinel indicate they record progress fronts replacement serpentine by carbonate addition dilatant growth. Euhedral terminations growth textures fill, together local dolomite precipitation voids along vein–wall interface, acted as preferred pathways allowing infiltration CO2-rich necessary for progress. Fracturing flow were probably further enabled external tectonic stress, indicated spaced subparallel Despite widespread subsequent quartz mineralization matrix veins, which most likely caused reduction network, proceeded completion within horizons.