In-situ growth of calcite at Devils Hole, Nevada: Comparison of field and laboratory rates to a 500,000 year record of near-equilibrium calcite growth

Calcite grew continuously for 500,000 years on the submerged walls of an op en fault plane (Devils Hole) in southern Nevada, U.S.A. at rates of 0.3 to 1.3 mm/ka, but ceased growing approximately 60,000 years ago, even though t he fault plane remained open and was continuously submerged. The maximum in itial in-situ growth rate on pre-weighed crystals of Iceland spar placed in Devils Hole (calcite saturation index, SI, is 0.16 to 0.21 at 33.7 degrees C) for growth periods of 0.75 to 4.5 years was 0.22 mm/ka. Calcite growth on seed crystals slowed or ceased following initial contact with Devils Hol e groundwater. Growth rates measured in synthetic Ca-HCO3 solutions at 34 d egrees C, CO2 partial pressures of 0.101, 0.0156 (similar to Devils Hole gr oundwater) and 0.00102 atm, and SI values of 0.2 to 1.9 were nearly indepen dent of P-CO2, decreased with decreasing saturation state, and extrapolated through the historical Devils Hole rate. The results show that calcite gro wth rate is highly sensitive to saturation state near equilibrium. A calcit e crystal retrieved from Devils Hole, and used without further treatment of its surface, grew in synthetic Devils Hole groundwater when the saturation index was raised nearly 10-fold that of Devils Hole water, but the rate wa s only 1/4 that of fresh laboratory crystals that had not contacted Devils Hole water. Apparently, inhibiting processes that halted calcite growth in Devils Hole 60,000 years ago continue today.