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Defining P-T conditions: multi-thermometric approaches to characterize the thermal evolution of the McDermitt Caldera plumbing system

Andrea Buian 1, Philipp Ruprecht1, Matthieu Harlaux2

  • Affiliations:  1 Nevada Geosciences, University of Nevada, Reno, NV 89557, USA; 2 BRGM -- French Geological Survey, 45060 Orléans, France. 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 237

  • Programme No: 1.1.23

  • Theme 1 > Session 1

Abstract

The McDermitt Caldera, a large peraluminous-peralkaline rhyolitic system that formed ~16 Ma during the onset of the Yellowstone hotspot track, has garnered attention for its Li-rich sedimentary deposits and geodynamic links to plume activity and Western US tectonics. The main volcanic activity that spanned 340 ka years has only received limited petrologic work. Here we integrate "TitaniQ" thermobarometry with additional thermometric methods to estimate P-T conditions of late-stage crystallization in both peralkaline and peraluminous rhyolites. By coupling this tool with cathodoluminescence imaging, XRF elemental mapping, and microscopy we link thermal evolution to textural information and shed light on late-stage magmatic processes and the pre-eruption history of the McDermitt system. Inferred temperature and pressure ranges of 790--900ºC were obtained using the calibration by Thomas et al. (2010). These results suggest a complex magmatic history characterized by significant temperature fluctuations and/or distinct rhyolitic magma bodies stored under variable conditions. However, the reliability of "TitaniQ" is debated due to uncertainties in aTiO2 in rutile-absent assemblages, though it provides accurate estimates when Ti-in-quartz is well-constrained. Using calibrations with aTiO2 values of 0.5--0.8 reveals a ±30ºC variability in temperature estimates. Complementary methods, the two-feldspar thermometer (Putirka, 2008), Fe-Mg exchange between biotite and melt (Holland & Blundy, 1994), and MELTS (Gualda, 2014), aim to address these discrepancies comparing different thermometric methods using other mineral phases in the rhyolitic assemblage. This comparative analysis evaluates thermometric precision and accuracy, identifies key influencing factors, and enhances thermobarometric applications in complex magmatic systems.