The accumulation of cosmogenic chlorine-36 in rocks: a method for surface exposure dating.

Because of the reaction of cosmic rays with elements in minerals, chlorine-36 accumulates in rocks exposed at the earth's surface. This suggests that the ratio of chlorine-36 to stable chloride can be used as a geochronometer. Reasonable agreement has been obtained between measurements of chlorine-36 in volcanic rocks of known age and calculations of chlorine-36 production based on rock composition and cosmicray flux. The buildup of chlorine-36 should be a useful means for measuring the surface exposure time of young volcanic rocks and geomorphic features in the age range of 10(3) to 10(6) years.