Lawrence Berkeley National Laboratory

Relationships between Cl and 3He concentrations, 3He/4He ratios and Br in Oregon Cascade volcanic arc hot and cold springs provide new evidence for the origin of the Cl in these springs. The relationship of Cl with 3He indicates that a significant part of the Cl in the hot and cold springs can be derived from a magmatic source located beneath the crest of the volcanic arc. Evidence for a second Cl component in the hotsprings is clearly present, but hard to distinguish given the resolution that the data provide. The most likely source for this component is Tertiary marine sediments that the thermal fluids encounter as they travel along long flow paths in deep aquifers to their discharge points away from the volcanic crest.