(U-Th)/He Thermochronology Lab

Facility Website
Director/PI: Rebecca Flowers
Facility Manager: James Metcalf
Location: Benson 225

The CU TRaIL is a fully-equipped (U-Th)/He thermochronology facility directed by Prof Rebecca Flowers and managed by Dr. James Metcalf. The lab was estab- lished in 2012 with an NSF Instrumentation award to purchase an ASI Alphachron. This automated He extraction and analysis system, optimized for reliably charac- terizing small gas amounts, is the heart of the CU TRaIL. Samples are loaded into an ultra-high vacuum chamber with a sapphire viewport attached to an automated stage. Individual mineral samples are degassed with a 50 Watt diode laser at temperatures of ~1000°C for 5-10 minutes. The evolved gas is then spiked with isotopically pure ³He, cleaned with active gettering systems, and finally analyzed with a Pfeiffer Balzers QME 220 quadrupole mass spectrometer. The Alphachron also has a diffusion cell capable of high-precision diffusion experiments used to better understand the He diffusion kinetics of different minerals.

A second NSF award in 2016 provided funds for a new Agilent 7900 quadrupole ICPMS that will be installed in summer 2017. This instrument will be equipped with a sample-introduction system that can withstand concentrated hydrofluoric acid and will be optimized for measuring trace element and isotopic compositions of dissolved silicate minerals. The new ICPMS will be primarily used to measure U, Th, and Sm contents of grains after He analysis.

(U-Th)/He dating is a widely applicable technique capable of constraining an enormous range of geologic processes, especially those that heat or cool rocks in the upper crust. Since opening in 2012, the lab has generated thousands of analyses for internal and external projects, and hosts numerous visitors annually. Scientists in the CU TRaIL research group have used (U-Th)/He dating to address questions at a variety of spatial and temporal scales, including the carving of Grand Canyon, the burial and unroofing history of continental plateaus and cra- tonic interiors, the uplift of the Colorado Front Range, and the impact history of the moon. The lab also is engaged in an array of method development studies that have involved analyses of phases not conventionally dated by (U-Th)/He, including conodonts, perovskite, baddeleyite, monazite, garnet, and rutile.