Postcollapse volcanism in the Valles Caldera, New Mexico: The transition from large volume explosive to small volume effusive eruptions

Deer Canyon, Redondo Creek, and Del Medio rhyolites were erupted in the Valles Caldera within 54 ka following caldera collapse. Postcollapse rhyolites and Bandelier Tuff magmas are compositionally distinct, and Deer Canyon is heterogeneous between individual flows. 238U/206Pb zircon dating shows that Redondo Creek zircons were derived from the residual Bandelier Tuff crystal mush system whereas Deer Canyon zircons were derived from remelting of a pluton at depth. Electron microprobe analyses of feldspars reveal complex zonation caused by interactions between mafic magmas and silicic melts of residual crystal mush as well as between distinct melts from the crystal mush. Each postcollapse rhyolite was produced by independent melting events in the residual Bandelier Tuff crystal mush, interactions between these melts and heat-providing mafic magmas, and magma arriving from deeper in the crust. They are not comagmatic with each other, nor with the preceding Bandelier Tuff magmas.