Carbon isotopic composition of solid carbon and C-H-O fluid produced through the decomposition of stearic acid under HP-HT condition

We estimated delta C-13 of the C-H-O fluid produced by the decomposition of stearic acid at high-pressure and high-temperature conditions (10 and 17 GPa, 800-1600 degrees C) from delta C-13 of the solid carbon products and the initial stearic acid. The delta C-13 of the stearic acid and the recovered graphite/diamond were -28.0 parts per thousand and -27.08 to -29.35 parts per thousand, respectively. Then, the delta C-13 of the coexisting C-H-O fluid was estimated to be -26.3 to -29.2 parts per thousand based on the stoichiometry of the decomposition reaction C18H36O2 -> 10C + 8CH(4) + 2H(2)O. In the studied P-T-t conditions, carbon isotope fractionation through the stearic acid decomposition is as small as < 3 parts per thousand. This means that the delta C-13 of the C-H-O fluid is almost identical to that of the initial stearic acid and can be a useful tracer of carbon source for diamond forming reaction such as in fluid/carbonate systems.