Geochronology of Precambrian metamorphic rocks, north-central New Mexico Available to Purchase

New K-Ar and Rb-Sr data have been obtained for Precambrian rocks of north-central New Mexico. K-Ar dates fall into one group with a mean of 1,325 ± 13 m.y. and another with a mean of 1,257 ± 21 m.y. The former conforms to the 1,350-m.y. B.P. event reported in previous literature. The latter defines a 1,250-m.y. B.P. event that is both tectonic and hydrothermal. Limited new Rb-Sr data support a 1,425-m.y. isochron. Thus, there are four events for the Precambrian rocks of northern New Mexico: (1) 1,673-m.y. B.P. intrusion of “Embudo Granite”; (2) 1,425-m.y. B.P. tectonic and metamorphic event accompanied by pegmatite emplacement; (3) 1,350-m.y. B.P. thermal event; and (4) 1,250-m.y. B.P. tectonic and hydrothermal event.