Saline water in the foothill suture zone, Sierra Nevada Range, California

摘要

Thirty-one wells yielding sodium chloride water and dissolved solids averaging 1,300 mg per liter have been drilled into granitic rocks of the western Sierra Nevada foothills of Fresno and Madera Counties, California. Their chemistry contrasts sharply with that of thousands of other wells tapping granitic rocks in the area which yield good quality bicarbonate water that is low in dissolved solids. The sodium chloride wells are along a N30°W, 85-km-long trend, herein referred to as the "foothill lineament." The foothill lineament appears to be an extension of the foothill suture into the intervening granitic terrane between the Melones Fault on the north and the Kings-Kaweah suture on the south. Based on various chemical parameters such as B/Cl and Br/Cl, the sodium chloride waters appear to be marine connate in origin, albeit strongly diluted with meteoric water. Several hypotheses are advanced to explain why saline waters are concentrated along the foothill lineament, although all arguments have serious drawbacks. No matter how the sodium chloride waters have originated, the foothill lineament is believed to define a profound structural element, possibly contiguous with the early Mesozoic foothill subduction complex, along which these waters have migrated toward the surface.