Insights from Zircon Geochronology and Trace Element Geochemistry on the Interplay of Plutonism and Volcanism within the Mount Princeton Magmatic Complex of Central Colorado

Combining high-precision CA-ID-TIMS zircon U/Pb geochronology with multivariate analysis of trace element data provides insight into the evolution of crustal magmatic systems. The Mt. Princeton magmatic center (MPMC) contains the largest Cenozoic batholith in Colorado (450 km^2) as well as volcanic rocks erupted from within or adjacent to the batholith boundary. Over a kilometer of vertical relief at the MPMC, caused by Rio Grande rifting and the collapse of the Mt. Aetna caldera, exposes a variety of volcanic and plutonic rocks, making the MPMC a well-suited locality to study the relationship between plutonism and volcanism. Here we present new U/Pb zircon geochronologic results for six samples from the MPMC which expand the duration of active magmatism for the system to 37.48 ± 0.18 Ma to 33.93 ± 0.08 Ma; excluding ~30 Ma leucogranites. The Calico Mt. Andesite flows and tuffs (37.48 ± 0.18) and the Mt. Pomeroy Quartz Monzonite (36.27 ± 0.09 Ma) preserved within the Mt. Aetna caldera collapse structure are interpreted as the earliest magmatism in the system. The age of the Calico Mt. volcanic rocks suggests they represent remnants of volcanic activity that predates all other dated rocks from the MPMC; and the age of the Mt. Pomeroy Quartz Monzonite places it as the oldest plutonic component of the MPMC. New U/Pb zircon geochronology results for rocks from the younger portion of the system suggest that the Badger Creek Tuff erupted at 34.35 0.08 and reveal complex zircon U/Pb isotopic mixing systematics within the Mount Aetna Quartz Monzonite. These new data along with previously published Ar/Ar ages provide evidence that subduction-related magmatism within the Mount Princeton Magmatic complex was active at least from 37.48 ± 0.18 to 33.93 ± 0.08 Ma, recording a systematic evolution from volcanism (37.48 ± 0.18) to large-volume plutonism (36.27 ± 0.09 to 35.37 ± 0.10) to ignimbrite related magmatism (35? – 33.93 ± 0.08 Ma). Integrated principal component analysis of trace element concentrations and high-precision ID-TIMS U/Pb geochronology reveals that these temporally distinct modes of magmatism also record distinct trace element signatures, suggesting that melt-producing processes are largely responsible for generating the chemical and temporal variation within the magmas of the Mt. Princeton magmatic complex.Bachelor of Scienc