Volcanic stratigraphy of the Barrel Springs--Wild Cherry Formations, Davis Mountains, Trans-Pecos Texas

Detailed mapping, stratigraphy, [sup 40]Ar/[sup 39]Ar ages, and geochemistry allow, for the first time, a coherent volcanic history of the Barrel Springs--Wild Cherry (BS-WC) units, the most widespread of the Davis Mountains volcanic field (DMVF). These units erupted dominantly from the [approximately] 20 km-diameter Paradise Mountain caldera (PMC), in the west-central DMVF, where thick, locally silicified and kaolinized intracaldera tuffs and interbedded lavas were resurgently domed by an 8 x 5-km-diameter syenitic intrusion. BS-WC units, all rhyolites, consist dominantly of a lower, moderately porphyritic ash-flow tuff; a petrographically similar, middle ash-flow tuff; and an upper group of voluminous, abundantly porphyritic lavas. The lower ash-flow tuff is strongly rheomorphic throughout its occurrence. The middle ash-flow is also rheomorphic in thick outcrops near the PMC but not in thin ([<=]10m), distal outcrops. These three units are interbedded with lavas lithologically similar to the tuffs near the PMC and with volcaniclastic sedimentary rocks in more distal area. The two ash-flow tuffs are separated by strongly porphyritic trachyte lavas of the Mount Locke Formation in the vicinity of the PMC. Sources and extents of individual flows of the upper lavas have not been positively identified. [sup 40]Ar/[sup 39]Ar ages of alkali feldspar phenocrysts frommore » thirteen samples constrain most BS-WC to a 300 ka span. The lower tuff erupted about 35.6 Ma. The middle tuff and part of the voluminous lava package erupted at 35.3 Ma. Ages of two lavas are 35.1 Ma, which suggests prolonged eruption. Correlations based on lithology and age relations are supplemented by trace element and mineral studies that confirm close geochemical affinities.« less