Zircon record of the plutonic-volcanic connection and protracted rhyolite melt evolution
Chad D. Deering, C. Brenhin Keller, Blair Schoene, Olivier Bachmann, Rachel Beane, and Maria Ovtcharova
Geology, 2016: https://doi.org/10.1130/G37539.1
The potential petrogenetic link between a crystal-poor rhyolite (the Rhyolite Canyon Tuff) and its associated subvolcanic intrusion and crystal-rich post-caldera lavas from Turkey Creek, Arizona (USA), is examined using zircon chemical abrasion–thermal ionization mass spectrometry U-Pb geochronology and inductively coupled plasma mass spectrometry trace element analyses. U-Pb ages indicate that zircon growth within the rhyolite and the dacite-monzonite porphyry magmas was coeval over ∼300 k.y. prior to the large eruptive event. Trends in zircon trace elements (Hf, Y/Dy, Sm/Yb, Eu/Eu*) through time in the dacitic-monzonitic units and rhyolite reflect melt evolution dominated by crystal fractionation. Importantly, the Y/Dy ratio in zircons in both units remains mostly similar for the first ∼150 k.y. of the system’s evolution, but the dominant population in the rhyolitic unit diverges from that of the dacite-monzonite porphyry ∼150 k.y. before eruption. We interpret this divergence in trace element composition to record the assembly time of the melt-rich cap within its intermediate mush zone in the upper crustal reservoir. These results are consistent with (1) a connection between plutonic and volcanic realms in the upper crust, (2) a protracted time scale for constructing an intermediate mush large enough to hold 500 km3 of rhyolite, and (3) the prolonged extraction of that melt prior to eruption.
Deering, C.D., Keller, C.B., Schoene, B., Bachmann, O., Beane, R., & Ovtcharova, M. (2016). Zircon Record of the Plutonic-Volcanic Connection and Protracted Rhyolite Melt Extraction. Geology 44 (4), 267-270.