Figure Caption. (a) Oxygen isotope compositions of Franciscan Complex (California) calcite/aragonite veins plotted vs estimated peak-T that the rocks have experienced. Also plotted are estimates of O-isotope compositions of aqueous fluids in equilibrium with the veins; O-isotope compositions of aqueous fluids in equilibrium with the host rocks; and O-isotope compositions of fluids in active accretionary complexes (fractionation factors from Friedman and O'Neil, 1977; Sharp and Kirschner, 1994). Note that most veins range from rock-buffered to slightly higher O-isotope compositions values. At relatively low-T, rock buffered values approach those of seawater. (b) Carbon isotope compositions of carbonate veins, most have C-isotope compositions similar to that calculated in equilibrium with the range in reduced C measured from these rocks (-27 to -21 per mil). On this figure, the ranges (patterned boxes) below the raw C data are calculated methane in equilibrium with the veins (presence of methane in lower-grade veins indicated by fluid inclusion analyses), and for methane in equilibrium with carbonaceous matter in these rocks. Figure is from Sadofsky and Bebout (2001, Geophysical Research Letters).