Publication Date

Fall 2014

Degree Type


Degree Name

Master of Science (MS)




Jonathan S. Miller


Cook Canyon Tuff, Geochronology, Ignimbrite, Peach Spring Tuff, Supereruption, Zircon

Subject Areas

Geology; Geochemistry; Petrology


The 18.8 Ma Peach Spring Tuff, Arizona, is a >600 km3 ignimbrite formed from the Miocene supereruption of Silver Creek caldera, Black Mountains, Arizona, and is an important Miocene stratigraphic bed in the southwestern United States. Peach Spring Tuff overlies the undated and less-voluminous Cook Canyon Tuff. Ion-microprobe and high-precision thermal ionization U-Pb dating of chemically abraded zircon crystals from Peach Spring Tuff and Cook Canyon Tuff reveal the crystallization history of both magma systems leading to eruption. A spread of U-Pb dates from ca. 18.1 to 22.0 Ma for Peach Spring Tuff relative to its 40Ar/39Ar age indicates variable Pb loss, with potential additional uncertainty due to complexities associated with 40Ar/39Ar dating. The youngest U-Pb crystallization date for Cook Canyon Tuff zircon crystals constrains the maximum eruption age to ca. 18.9 Ma, and indicates that eruption of the Cook Canyon Tuff preceded the Peach Spring Tuff eruption by no more than 2-3 x 105 years. The complex U-Pb zircon age spectra for both units indicate several 105 years of pre-eruptive magma residence, likely in a crystal mush state. When combined, the ages and trace elements for Peach Spring Tuff and Cook Canyon Tuff zircon crystals suggest that these two silicic magmas were derived from discrete but temporally and spatially overlapping magma systems.