RE-EVALUATING THE EMPLACEMENT HISTORY OF THE CORNUDAS MOUNTAINS

The Cornudas Mountains are a group of alkaline plugs and sills expressed as 9 prominent mountains with minor outcrops of dikes and breccias straddling the New Mexico- Texas line approximately 60 miles east of El Paso. These intrusions have been described in the past, but speculation on the emplacement mechanisms and evolution of the magmatism has not been evaluated since the 1970s. The Cornudas Mountains have recently become of interest because of their economic potential for rare earth elements and industrial minerals. Rare earth bearing minerals such as bastnaesite and eudialyte have been reported and are presently being assessed. The emplacement history of these mountains is poorly understood, and being updated to help direct rare earth exploration. ⁴⁰Ar/ ³⁹Ar dating of minerals and ground mass from the intrusions and dikes are used to understand the emplacement history. Preliminary data show a longer record of emplacement between ~40 Ma and ~25 Ma, rather than the previously understood shorter emplacement between around 37-31 Ma. We are pairing updated geochronology with mineral and whole rock chemistry of each intrusion to determine the temperature and depth of emplacement. This data can also be used to calculate exhumation rates and determine if the Cornudas Mountains were exhumed purely by erosion or if there was a tectonic component to the exhumation. The location and timing of the emplacement and subsequent exhumation of the Cornudas Mountains could be valuable to understanding regional Basin and Range and Rio Grande Rift extension.