Measurement of cosmogenic 36Cl/Cl in young volcanic rocks: an application of accelerator mass spectrometry in geochronology

Abstract

We have measured 36Cl/Cl ratios in a number of young volcanic rocks in order to test the feasibility of using 36Cl buildup as a geochronometer for materials less than about 700000 years old. All of the analyzed rocks have been dated independently using K-Ar or other radiometric dating methods and have exposure histories that are known or can be reasonably assumed. Measured 36Cl/Cl ratios in these rocks show a buildup with time that is in good agreement with the calculated in situ 36Cl buildup curve. These analyses indicate that AMS measurement of 36Cl buildup in young rocks is a potentially powerful new method for dating materials that had previously been undatable, and as such will have broad applications in volcanology, tectonics, geophysics, and Quaternary research.