Fig. 2. Negative log of the aqueous SiO₂ concentration in fractures and matrix as a function of time at about 200 and 400 m, for the conditions represented in Fig. 1. The negative log of the aqueous SiO₂ concentrations associated with surface temperature change are plotted as red lines, and those associated with surface flux change are plotted as blue lines. Fracture waters are represented as dashed lines, and matrix waters by solid lines. The curves have been plotted such that the time at which the perturbations were initiated exactly correspond, and 4000 yr of the initial steady-state conditions are shown.