New Mexico Geological Society Annual Spring Meeting — Abstracts

High-precision ⁴⁰Ar/³⁹Ar ages of late-Quaternary monogenetic basaltic volcanoes in the Raton-Clayton volcanic field, northeastern New Mexico characterize time-space patterns of eruptions and allow assessment of volcanic hazards. Determining eruption periodicity and durations of eruptive cycles are fundamental for volcanic hazard assessment. A previous ⁴⁰Ar/³⁹Ar study concluded that volcanism in the field began at ~9 Ma and ended at ~56 ka with the eruption of the well-known Capulin volcano. However, this chronology is not sufficiently precise or complete for a comprehensive volcanic hazard assessment. High-precision ages for this study were determined using a low-volume, high-sensitivity, multi-collector ARGUS VI mass spectrometer, which yields about an order of magnitude more precise isotopic measurements compared to older generation, single-detector mass spectrometers. New ⁴⁰Ar/³⁹Ar ages indicate 1) sparse volcanic activity between 200 and 500 ka, 2) eruptions from two centers at ~100 ka, and 3) a significant pulse of volcanism between ~32 and 55 ka including as many as three eruptions that are younger than Capulin volcano. Eruptions prior to 200 ka include the 426 ± 8 ka Las Maetas South center and 240 ± 7 ka Horseshoe Crater, which are both located to the south of Capulin volcano. The Trinchera Pass volcano, located near the New Mexico-Colorado border, erupted at 113 ± 7 ka. Volcanism shifted back to the southern part of the field where numerous lava flows erupted from The Crater cinder cone. A stratigraphically low lava flow at The Crater yielded an age of 97 ± 3 ka, whereas a lava flow on the flanks of The Crater yielded an indistinguishable age of 103 ± 5 ka indicating the volcano is monogenetic. Finally, volcanic activity migrated to the vicinity of Capulin volcano. Our new age for Capulin volcano is 55 ± 2 ka. This new age is indistinguishable from, but more precise than the previously determined age of 56 ± 8 ka. Baby Capulin is located ~4 km north of Capulin volcano. Multiple analyses of lavas from this center yielded an age of 46 ± 4 ka. East of Baby Capulin is Twin Mountain volcano, which yielded an age of 40 ± 4 ka. The youngest dated center in the field is Purvine Hills, three east-west aligned vents likely representing a fissure eruption. The ⁴⁰Ar/³⁹Ar age of Purvine Hills is 32 ± 5 ka. Electron microprobe analyses of spinel inclusions in olivine were conducted to assess the source of the 46 ± 15 ka Folsom Falls lava flow. Subtle variation in Cr₂O₃ and MgO/FeO ratios suggest that the Folsom Falls lava is the distal flow of the Baby Capulin lava flow. Ages and associated uncertainties indicate recurrence rates of 0 ka to as much as 17 ka for this youngest phase of volcanism in the Raton-Clayton field. New ⁴⁰Ar/³⁹Ar ages demonstrate the unprecedented capabilities of the ARGUS VI mass spectrometer, which is currently being used to assess temporal-spatial patterns at all late Quaternary volcanic centers in the Rio Grande rift and along the Jemez lineament.