Strontium 87/strontium 86 ratios as tracers in groundwater and surface waters in Mono Basin, California

The Sr-87/Sr-86 isotope ratios in spring waters in Mono Basin, California, are highly variable and reflect contact with different rock types. Whole rock Sr-87/Sr-86 ratios throughout the basin range between 0.7054 and 0.7281. Ratios in surface water samples differ greatly between runoff from the mainly granitic Sierra (0.7094-0.7097) and runoff from the volcanic regions (0.7054-0.7064). The ratio in Mono Lake water (0.7096) is similar to the ratios of streams from the Sierra Nevada. Springs close to the western shoreline have more radiogenic Sr ratios (0.7092-0.7100), while those on the east side have ratios (0.7081-0.7088) indicative of a mixture of water from the volcanic terrain and Mono Lake. Thermal springs at the south side of the lake have Sr-87/Sr-86 ratios of 0.7081-0.7089 and might originate in Paleozoic limestones at depth.