New Mexico Geological Society Annual Spring Meeting — Abstracts

Geologic mapping and ⁴⁰Ar/³⁹Ar geochronology in the west-central San Mateo Mountains of southwestern New Mexico suggest that the Nogal Canyon Cauldron (source cauldron of the Vicks Peak Tuft) is larger than previously proposed and was a topographic high until at least 27.4 Ma. Six kilometers northwest of the generally accepted cauldron margin, more than 290 m of Vicks Peak Tuff with no exposed base is found overlain by 260 m of rhyolite lavas. Several granite porphyries intrude this sequence. The Vicks Peak Tuff, rhyolite lavas and granite porphyries were all emplaced over a <90 k.y. span (28.23 to 28.32 Ma). The thickness of the Vicks Peak Tuff and the occurrence of lava domes and intrusions indicate that the margin of the Nogal Canyon Cauldron is actually north of the field area. Overlying the lava domes and intrusions are a thin sequence of volcaniclastic sediments and the 24.3 Ma Turkey Springs Tuff. Missing from this stratigraphy is the 27.4 Ma South Canyon Tuff, a regional ignimbrite that came from a cauldron less than 15 km to the north. This suggests that the Vicks Peak Tuff, domes and intrusions formed a topographic high during the 27.4 Ma eruption of the South Canyon Tuff. This topographic high probably formed by some combination of pre-cauldron uplift, resurgent uplift, and rapid lava dome accumulation.