Flow rates and reaction rates in the Galapagos Rise spreading center hydrothermal system as inferred from 228 Ra/ 226 Ra in vesicomyid clam shells

The (228)Ra/(226)Ra ratios in a previously dated vesicomyid clam shell were used to determine that seawater was in contact with mid-oceanic-ridge basalt glass for 22-45 years prior to arrival to the surface at 350 degrees C at the Galapagos Rise Spreading Center. The minimum rate of reaction for the 45-year sojourn time, based on a water/rock ratio of 2.8 derived from (226)Ra concentrations, is 8 g of basalt altered per kg of seawater per year.