304 Integrating Geochronology and Geochemistry to Decipher the Tectonic Evolution of Orogenic Belts (Posters)
This session focuses on deciphering magmatic, metamorphic, depositional and deformational events recorded in orogenic belts via the integration of geochemistry and geochronology. We welcome contributions from modern applications of analytical methods aimed at unraveling orogenic events worldwide, fostering interdisciplinary discussion.
Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1
Best Practices in Monazite-Xenotime Thermometry and an Example from the Caledonides of northern Scotland
Paper number: 304-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
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Mark CaddickVirginia Tech, Dept. Geosciences, Derring Hall (0420), Blacksburg, VA
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Richard LawVirginia Polytechnic Inst & State UnivDepartment of Geosciences, Blacksburg, VA
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Ryan ThigpenUniversity of Kentucky, Lexington, KY
Abstract
Monazite-xenotime thermometry is a long-established petrochronologic tool that can provide critical information for deciphering the evolution of dynamic earth systems. However, the interpretation of monazite-xenotime data is challenging because five published calibrations all yield different results, and uncertainty persists regarding how complex natural monazite compositions relate to simplified experimental systems. We used a compilation of published natural and experimental monazite and xenotime compositions and independently established metamorphic temperatures to evaluate existing calibrations and clarify aspects of the practical usage of the technique. In general, calibrations based on natural data are more successful than simplified experimental systems in reproducing independently determined metamorphic temperatures. Published experimental data on Y-Ce-Th and Y-Ce-Gd systems reveal that Y-Ce partitioning is highly composition dependent. Thus, simplified experimental systems are unlikely to provide meaningful direct calibrations of elemental partitioning in natural monazite-xenotime systems. A more helpful approach may be to treat light and heavy rare earth element end-members as thermodynamic components.
We have applied the best-fitting monazite-xenotime calibration to samples from the Northern Highlands terrane of Scotland, which experienced upper greenschist to amphibolite facies metamorphism and penetrative deformation during the Scandian orogeny. Thermometry data in conjunction with U–Pb geochronology reveal a relatively slow initial regional cooling (12 ± 3˚C Myr-1) across the Scandian thrust nappes, followed by accelerated cooling and exhumation. Monazite-xenotime and quartz c-axis deformation thermometry are in close agreement, suggesting that monazite and xenotime record the timing and temperature of penetrative deformation and shearing. Taken together, these data suggest that ductile deformation in the hinterland nappes of the Scandian orogen in Scotland occurred as late as 415–410 Ma.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-413522
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