Although the (U-Th)/He dating technique is calibrated against first principles and does not require standardization, it is invaluable to have mineral standards to monitor procedural performance and to use as benchmarks by which to judge the quality of results and for inter-laboratory comparison.
The UT (U-Th)/He laboratory regularly analyzes a variety of recognized, inter-laboratory, and intra-laboratory standards, such as Durango apatite (~31.5 Ma; Young et al., 1969; McDowell and Keizer, 1977, Farley, 2000), Fish Canyon Tuff apatite and titanite (~27.9 Ma; see summary in Villeneuve et al., 2000), and 97MR22, a well-characterized plutonic sample from British Columbia (4.5 Ma; Farley et al., 2001). Our measured ages for these age standards are in excellent agreement with published values, giving us confidence in the quality of our data and the performance of our multi-step laboratory procedures.
Over the years the active (U-Th)/He laboratories have used a series of quickly-cooled standards that fall into three categories, (1) regular age standards dated by other analytical techniques, such as 40Ar/39Ar dating (e.g., Fish Canyon Tuff), (2) semi-formal standards used by the leading (U-Th)/He laboratories as inter-laboratory standards (e.g., 97MR22 distributed by Caltech), and (3) intra-laboratory standards that have been independently dated and/or have proven to yield extremely well-behaved and reproducible age data. All three types of standards are in use at the UT (U-Th)/He laboratory.
Co-analyzed standard data will be included in both the analytical report as well as the electronic database (see below). The summary table below documents all commonly used age standards dated in our laboratory over the past three years, listing mean (U-Th)/He age (2-s), number of analyses (n), the relative standard deviation of the population, and the accepted 40Ar/39Ar age. For monazite, rutile, and magnetite only informally developed by Stockli’s group/laboratory, but independently dated intra-laboratory standards exist.
Summary Table of (U-Th)/He age standards most commonly analyzed at the KU/UT (U-Th)/He laboratory to monitor procedural integrity and age reliability (see text). n denotes the number of aliquot analyses carried out at KU/UT (U-Th)/He laboratory during the past 3 years.
Summary of UT (U-Th)/He age standards
|Standard (Mineral)||Rock type||(U-Th)/He age [Ma]||n||RSD%||40Ar/39Ar age [Ma]|
|Durango (apatite)||Rhyolite||31.9 ± 0.5||161||3.5||31.5|
|97MR22 (apatite)||Tonalite||4.4 ± 0.1||225||6.5||4.5*|
|Silver Peak Tuff (apatite)||Rhyolite||6.4 ± 0.2||45||8.7||6.5|
|Fish Canyon Tuff (zircon)||Rhyolite||27.8 ± 0.8||162||7.5||28.2|
|Silver Peak Tuff (zircon)||Rhyolite||6.4 ± 0.3||39||8.7||6.5|
|Taylor Creek (zircon)||Rhyolite||28.8 ± 0.8||26||8.8||28.3|
|Wall Mountain Tuff (zircon)||Rhyolite||36.2 ± 1.1||38||7.8||36.8|
|Fish Canyon Tuff (titanite)||Rhyolite||28.7 ± 1.2||53||2.2||28.2|
|Silver Peak Tuff (titanite)||Rhyolite||6.5 ± 0.4||29||4.3||6.5|
|Macusani (monazite)||Rhyolite||24.2 ± 0.4||11||5.2||24.2|
|Sulliavan Buttes (rutile)||Xenolith (latite)||23.1 ± 1.4||35||5.7||24.4|
|Sweet Grass (rutile)||Xenolith (latite)||48.1 ± 3.9||13||8.7||50-54|
*reference age is published (U-Th)/He age; sample used by several laboratories as intra- and inter-laboratory age standard.
Duango Apatite Age Standard (2004)