Cosmogenic 36Cl-determined age of the Carrizozo lava flows,

south-central New Mexico, U.S.A.

Nelia W. Dunbar

New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM, 87801

The Carrizozo lava flows, in south-central New Mexico, are one the of the youngest-appearing volcanic features in the state. Cosmogenic 36Cl dating of the two basaltic pahoehoe flows, yields an eruption age of 5200 700 yrs ago. There is no apparent age difference between the upper and lower Carrizozo flows, suggesting that this lava field was formed by a monogenetic event. The determined age is in good agreement with secular variation magnetostratigraphy and 3He ages, but is much older than ages based on visual observations of the flow surface morphology and archeological evidence. The 36Cl age of the Carrizozo lava flows is consistent the 36Cl and 14C ages determined for the McCarty's flow, also in New Mexico, which, based on geomorphic features, appears slightly younger than the Carrizozo flows.