18O values establish that waters are predominantly of meteoric origin. The chemical compositions of water and gases are controlled mainly by the ambient rock types, and chemical geothermometry gives reservoir temperatures of 80-150 degrees C indicating shallow to moderate circulation depths of up to 6 km. However, compositions and isotope abundances of noble gases and delta 13C values of HCO3 indicate a significant (up to 50%) mantle component for the volatiles. The relatively high fluxes of CO2 (C/ 3He nearly equal 10 10) and other volatiles of mantle origin support a deep continuous flow model, especially at depths >6 km. Numerical simulations indicate that these high fluxes of CO2 of mantle and deep crustal origin are sufficient to generate lithostatic fluid pressures, and thus a weakened fault, in time scales comparable to those of earthquake cycles.
|Title||Geochemistry and hydromechanical interactions of fluids associated with the San Andreas fault system, California|
|Authors||Yousif K. Kharaka, James J. Thordsen, William C. Evans, B. Mack Kennedy|
|Publication Type||Book Chapter|
|Publication Subtype||Book Chapter|
|Record Source||USGS Publications Warehouse|
|USGS Organization||National Research Program - Western Branch|