Date of Graduation

Spring 2017


Master of Science in Geospatial Sciences


Geography, Geology, and Planning

Committee Chair

Gary Michelfelder


zircon, geochronology, ignimbrite flare-up, MDVF, New Mexico

Subject Categories

Geochemistry | Volcanology


Caldera systems are capable of outputting voluminous quantities of volcaniclastic material with wide ranging negative environmental impacts. Determining the behaviors of previously erupted caldera systems may help inform predictive models used to evaluate hazards and assess risks for analogous currently active volcanic systems. The Mogollon-Datil volcanic field (MDVF) is a 40-24 Ma cluster of caldera activity in southern New Mexico tied to the subduction, and possible delamination, of the Farallon plate beneath the North American plate. A regional ignimbrite flare up from 36-24 Ma produced at least 28 caldera-forming eruptions. The calc-alkaline magmatism of three calderas in this field (the Mogollon, Bursum, and Gila Cliff Dwellings) produced several voluminous and regionally dispersed ash-flow tuffs. Magmatic zircon sampled from these tuffs record timescales of magmatic accumulation via U-Pb isotopic zonation. This study focuses on analysis of zircon crystals and the utilization of U-Pb isotope ratios as geochronometers for magmatic activity in the MDVF. I present new U-Pb geochronology results obtained via Sensitive High Resolution Ion Microprobe-Reverse Geometry (SHRIMP-RG) analysis of magmatic zircon from five MDVF ignimbrites. I compare previous geochronology results obtained via 40Ar/39Ar in sanidine to new U-Pb zircon age dates (1σ error), Pb isotopic ratios, and trace element compositions in the zircon samples.


© Shannon Porter Rentz

Open Access