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Natural CO₂ discharges are abundant in Turkey as evident from ongoing deposition of recent terrace-mound travertines and emplacement of significant travertine vein and breccia deposits in fractured damage zones of active fault systems. We report high-precision U-series age data for the vein carbonates combined with important field observations and geochemical data to evaluate the travertine veining and CO₂ degassing history in seismically active areas. Field evidence suggests that travertine-filled veins and associated breccias represent hydrothermal eruption products, which probably formed by hydraulic fracturing in response to overpressure of CO₂-rich fluids. Stable isotope and REE data support the field observations and indicate that travertine veins formed as thermogene deposits from rapidly ascending CO₂-rich fluids. Travertine veins from the Kirsehir geothermal field give U-series ages in a range …