MULTIPLE RESURGENCE EVENTS OF THE BURSUM CALDERA, SW NEW MEXICO, RECORDED IN THE FANNEY RHYOLITE

The Mogollon-Datil Volcanic Field (MDVF) located in southwestern New Mexico showcases volcanism representing the transition from ignimbrite flare-up to small volume basaltic andesite systems between 40 Ma and 24 Ma. The last gasp of rhyolite magmatism during this transition is recorded in the resurgent domes of the Bursum caldera and are known as the Fanney Rhyolite. Understanding the spatial distribution of eruptive centers and heterogeneity of the Fanney Rhyolite in time and space will allow for a better understanding of the transition between large volume rhyolite volcanism in the MDVF to small volume basaltic systems between 28-24 Ma. We present U-Pb zircon ages and trace element contents analyzed by laser ablation ICP-MS for twelve new rhyolite samples from the Fanney Rhyolite. For each sample we analyzed between 35-50 zircon grains analyzing both cores and rims when possible. Rhyolite samples from the Fanney Rhyolite and the Deadwood Gulch member of the Fanney Rhyolite range in U-Pb zircon crystallization age from 25.36±0.25 Ma to 27.23±0.23 Ma. Eu/Eu*, Yb/Gd ratios, and Hf contents show two populations of zircons in the Fanney Rhyolite, one representing cold storage and one representing remobilization of the magma prior to eruption. This suggests that the Fanney Rhyolite represents more than one stage of resurgence during the transition from ignimbrite volcanism to small volume basaltic systems.