Cosmogenic chlorine-36 production rates in terrestrial rocks

Chlorine-36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of 35C1, spallation of 39K and 't°Ca, and slow negative muon capture by 4°Ca. We have measured the 36C1 content of 14C-dated glacial boulders from the White Mountains in eastern California and in a 14C-dated basalt flow from Utah. Effective, time-integrated production parameters were calculated by simultaneous solution of the 36Cl production equations. The production rates due to spallation are 4160 + 310 and 3050 + 210 atoms 36C1 yr 1 tool 1 39 K and 4°Ca, respectively. The thermal neutron capture rate was calculated to be (3.07 + 0.24) × 105 neutrons (kg of rock) 1 yr ~. The reported values are normalized to sea level and high geomagnetic latitudes. Production of 36C1 at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates. Chlorine-36 dating was performed on carbonate ejecta from Meteor Crater, Arizona, and late Pleistocene morainal boulders from the Sierra Nevada, California. Calculated 36C1 ages are in good agreement with previously reported ages obtained using independent methods.