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Smith Lecture: Insights into Rhyolite Production at a Frequently Active Silicic Center as Revealed by Quartz δ18O Ratios

Mai Sas, Western Washington University
Friday, March 26, 2021
3:30-4:30 PM
Zoom ID# 96255483493

Located in the Taupo Volcanic Zone of North Island, New Zealand, the Okataina Volcanic Centre (OVC) is a frequently active, largely rhyolitic magmatic system that is situated in a coupled subduction-extension setting. Rhyolite production at the OVC is a result of fractional crystallization of mantle-derived basalt that is heavily contaminated by crustal components. However, questions remain over the extent of crustal contamination and how contributions from the mantle versus the crust have fluctuated over the lifespan of the OVC. In this study we aim to answer these questions using intra-crystal and single-crystal oxygen isotopic ratios (δ18O) of rhyolite-hosted quartz. We use δ18O ratios because (1) they are minimally impacted by fractional crystallization, (2) at the OVC, they allow for better differentiation among possible contributing sources (i.e., mantle, crust, hydrothermally altered shallow crust) than radiogenic isotopes alone, and (3) even minor fluctuations in δ18O ratios indicate significant changes in the mass of contributing sources. Results reveal homogenous δ18O ratios that indicate consistent mass contributions from mantle and crustal sources, with significant assimilation (≥20 %) of surrounding metasedimentary crust, across the 0.6 Ma lifespan of the OVC magmatic system. These findings differ from δ18O ratios observed in silicic systems that are situated in hot spot or subduction settings, which exhibit large (>1.0 ‰) fluctuations in quartz δ18O ratios. However, these findings resemble δ18O ratio fluctuations (or lack thereof) observed in silicic systems that are situated in extensional settings, indicating that extension is largely responsible for magma flux and processes occurring at the OVC.
Building: Off Campus Location
Location: Virtual
Event Link:
Event Type: Lecture / Discussion
Tags: Lecture
Source: Happening @ Michigan from Earth and Environmental Sciences