Radiometric Age Determinations from the Florida Mountains, New Mexico

Abstract

Most of the igneous rocks of the Florida Mountains, New Mexico, can be divided into three groups: (1) old (∼1.35 b.y.?) granitic rocks in the northernmost part of the area; (2) granite to (quartz) syenite of uncertain age that occurs south of the major high-angle reverse fault that roughly divides the Florida Mountains into northern and southern parts (Corbitt, 1971; Corbitt and Woodward, 1973); and (3) enigmatic syenitic rocks of uncertain age that occur north of the major high-angle reverse fault. Corbitt (1971) has proposed a Mesozoic age of emplacement for the group 3 rocks, although Griswold (1961) has placed them in the Precambrian; minor mineralization is more-or-less confined to occurrences within or near the syenitic rocks. This report summarizes preliminary geochronologic data for the major occurrences of syenitic or quartz syenitic to granitic rocks from the Florida Mountains and will attempt to interpret their history. K-Ar and Rb-Sr mineral and Rb-Sr whole-rock age data indicate a complex history; geochemical and normative data are included for assistance in interpretation.