scholarly journals Technical note: apatite and zircon (U-Th)/He analysis using quadrupole and magnetic sector mass spectrometry

2021 ◽  
Author(s):  
Cécile Gautheron ◽  
Rosella Pinna-Jamme ◽  
Alexis Derycke ◽  
Floriane Ahadi ◽  
Caroline Sanchez ◽  
...  

Abstract. Apatite and zircon (U-Th)/He thermochronological data are obtained through a combination of crystal selection, He content measurement by extraction from crystal and analysis using noble gas mass spectrometry, and measurement of U, Th and Sm contents by dissolution and solution analysis using inductively coupled plasma mass spectrometry (ICP-MS). In this contribution, we detail the complete protocols developed for over more than a decade 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 a high precision using a calibration of the He sensibility based on the Durango apatite and its use also appears crucial to check for He, U-Th-Sm analytical problems. The Durango apatite used as a standard is therefore a suitable mineral to perform precise He calibration and yield (U-Th)/He ages of 31.1 ± 1.4 Ma with an analytical error of less than 5 %. The (U-Th)/He ages for the FCT zircon standard yields a dispersion of about 9 %, with mean age of 27.0 ± 2.6 Ma comparable to other laboratories. For the long-term quality control of the (U-Th)/He data, attention has been paid to evaluate the drift of He sensibility, blanks through time and those of (U-Th)/He ages and Th/U ratios (with Sm/Th when possible), all associated with the use of Durango apatite and Fish Canyon Tuff zircon as standards.

Geochronology ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 351-370
Author(s):  
Cécile Gautheron ◽  
Rosella Pinna-Jamme ◽  
Alexis Derycke ◽  
Floriane Ahadi ◽  
Caroline Sanchez ◽  
...  

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 % (1σ). The (U–Th) / He ages for the Fish Canyon Tuff zircon standard yield a dispersion of about 9 % (1σ) 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.


Geochronology ◽  
2020 ◽  
Vol 2 (1) ◽  
pp. 155-167
Author(s):  
Marcel Guillong ◽  
Jörn-Frederik Wotzlaw ◽  
Nathan Looser ◽  
Oscar Laurent

Abstract. We document that the reliability of carbonate U–Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is improved by matching the aspect ratio of the LA single-hole drilling craters and propagating long-term excess variance and systematic uncertainties. We investigated the impact of different matrices and ablation crater geometries using U–Pb isotope analyses of one primary (WC-1) and two secondary reference materials (RMs). Validation RMs (VRMs) include a previously characterised one (ASH-15D) and a new candidate (JT), characterised by ID-TIMS (intercept age: 13.797±0.031 Ma) with excellent agreement to pooled LA-ICP-MS measurements (13.75±0.11 | 0.36 Ma), a U concentration of approx. 1 µg g−1 and 238U∕206Pb ratios from 5 to 460, defining the isochron well. Differences in ablation crater depth to diameter ratios (aspect ratio) introduce an offset due to downhole fractionation and/or matrix effects. This effect can be observed either when the crater size between U–Pb RM and the sample changes or when the ablation rate for the sample is different than for the RM. Observed deviations are up to 20 % of the final intercept age depending on the degree of crater geometry mismatch. The long-term excess uncertainty was calculated to be in the range of 2 % (ASH-15D) to 2.5 % (JT), and we recommend propagating this uncertainty into the uncertainty of the final results. Additionally, a systematic offset to the ID-TIMS age of 2 %–3 % was observed for ASH-15D but not for JT. This offset might be due to different ablation rates of ASH-15D compared to the primary RM or remaining matrix effects, even when the aspect ratios chosen are similar.


2020 ◽  
Author(s):  
Fanis Abdullin ◽  
Luigi Solari ◽  
Jesús Solé ◽  
Carlos Ortega-Obregón

Abstract. The same unetched and chemically etched apatites from five rock samples were dated with U–Pb using laser ablation inductively coupled plasma mass spectrometry. The objective of this study is to demonstrate whether or not the etching, needed for the apatite fission track analysis, impact on the obtaining of apatite U–Pb ages. The results of this experiment indicate that the etching has no effect on the determination of apatite U–Pb ages by the laser ablation inductively coupled plasma mass spectrometry technique. Thus, laser ablation inductively coupled plasma mass spectrometry may be used safely for simultaneous apatite fission track in-situ and U–Pb double dating.


2019 ◽  
Author(s):  
Ingo Strenge ◽  
Carsten Engelhard

<p>The article demonstrates the importance of using a suitable approach to compensate for dead time relate count losses (a certain measurement artefact) whenever short, but potentially strong transient signals are to be analysed using inductively coupled plasma mass spectrometry (ICP-MS). Findings strongly support the theory that inadequate time resolution, and therefore insufficient compensation for these count losses, is one of the main reasons for size underestimation observed when analysing inorganic nanoparticles using ICP-MS, a topic still controversially discussed.</p>


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