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Geochemistry and geochronology of Quaternary mafic volcanic rocks in the vicinity of Carrizozo, New Mexico

-We report here elemental and chronologic information for the Quaternary lavas from the vicinity of Carrizozo, New Mexico. The geochemistry of these lavas is transitional between hypersthene and nepheline normative and is very similar to other lavas in the region, e.g., the Jornado del Muerto volcanic field. The mag matic noble gas signature, here given in terms of3He/'He, correlates well with radiogenic isotopes and indicates that the magmas either were derived from a mantle source more enriched in incompatible elements than aver age asthenosphere or have seen some crustal contamination. We have measured the age of the Carrizozo upper flow using 3 He cosmogenic surface exposure dating. The age of 4800 ± 1700 yrs before present (ybp) agrees well with other recent determinations. The Broken Back portion of the field is older. Cone morphology and degree of surficial alteration of magnetite to hematite, as deduced from remote sensing, indicates that the cones may be approximately 100 ka old.