Technical note: Analytical protocols and performance for apatite and zircon (U–Th) ∕ He analysis on quadrupole and magnetic sector mass spectrometer systems between 2007 and 2020
2021
Abstract. Apatite and zircon (U–Th) / He thermochronological data are
obtained through a combination of crystal selection, He content measurement
by crystal heating with analysis using noble gas mass spectrometry, and
measurement of U, Th, and Sm contents by crystal dissolution as well as solution
analysis using inductively coupled plasma mass spectrometry (ICP-MS). This
contribution documents the methods for helium thermochronology used at the
GEOPS laboratory, Paris-Saclay University, between 2007 and the present
that allow apatite and zircon (U–Th) / He data to be obtained with precision.
More specifically, we show that the He content can be determined with
precision (at 5 %) and accuracy using a calibration of the He sensitivity
based on the Durango apatite, and its use also appears crucial to check for
He and U–Th–Sm analytical problems. The Durango apatite used as a standard is
therefore a suitable mineral to perform precise He calibration and yields
(U–Th) / He ages of 31.1 ± 1.4 Ma with an analytical error of less than 5 % (1 σ ). The (U–Th) / He ages for the Fish Canyon Tuff zircon standard yield a dispersion of about 9 % (1 σ ) with a mean age of 27.0 ± 2.6 Ma, which is comparable to other laboratories. For the long-term quality control of the (U–Th) / He data, attention is paid to evaluating the drift of He sensitivity and blanks through time as well as that of (U–Th) / He
ages and Th / U ratios (with Sm / Th when possible), all relying on the use of
Durango apatite and Fish Canyon Tuff zircon as standards.
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