INVESTIGATING POST EMPLACEMENT COOLING HISTORIES AND TECTONIC CAUSE OF EXHUMATION OF IGNOUS INTRUSTIONS IN EL PASO, TX USING APATITE (U-TH)/HE DATA

The El Paso region of westernmost Texas has experienced multiple episodes of Cenozoic tectonic uplift and erosion. Within this area, several relatively small andesitic intrusive bodies crop out including: the Campus Andesite, Coronado Hills, Cristo Rey, and Three Sisters. Based on geochemical and geophysical studies, the intrusive rocks are genetically related and thought to be the exposed portions of a larger body that underlies much of western El Paso and northern Ciudad Juárez area. Where exposed, this body intrudes into Cretaceous strata, and a two published K-Ar dates suggests that it was intruded 47.1 ± 2.3 Ma, during the waning stages of the Laramide Orogeny. Although previous research has focused on the mineralogy and petrology of this unit, no work has been done to constrain the exhumational history of these intrusions. In order to investigate their post-emplacement history, four samples were collected for apatite (U-Th)/He (AHe) analyses from the Campus Andesite, Coronado Hills, Cristo Rey, and Three Sisters. Five single-grain AHe ages per sample are being obtained. The data will be modeled using HeFTy software in order to provide approximate times of exhumation for each intrusion. The results will be compared to existing AHe ages from the nearby Franklin Mountains to determine if the exhumation and erosion of the intrusive bodies were temporally related to the Laramide Orogeny, or to deformation related to the development of the Rio Grande rift.