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

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.

Origins and Implications of the Apollo 16 Breccia Noble Gas Suite

<p>The Apollo 16 landing site is dominated by regolith breccias; consolidated regolith palaeo-soils [5,7,8]. Each regolith soil (and, by extension, each regolith breccia) is composed of fragments of rock sourced from different impacts and lithological units [e.g. 2,3]. Because of this, these samples probe the impact history of the lunar surface across a wide range of time. McKay et al. (1986) reported the trapped argon isotope ratios (i.e., <sup>40</sup>Ar/<sup>36</sup>Ar<sub>Tr</sub>) values of regolith breccias and used these values to semi-quantitatively model breccia formation ages [see also 4]. Two groups of regolith breccias were identified at the Apollo 16 landing site: (i) the ‘ancient’ group, lithified immature regolith (i.e., <30 I<sub>s</sub>/FeO), and (ii) a ‘younger’ group that generally have higher levels of maturity. Joy et al. (2011) used the <sup>40</sup>Ar/<sup>36</sup>Ar<sub>Tr</sub> ratios to model that: (i) the ancient samples closed from soils to breccias between ~3.8 and 3.4 Ga, consistent with regolith developed and consolidated after the Imbrium basin-forming event, and during a time of declining basin-forming impacts, and (ii) that the young breccias were assembled in the Eratosthenian period between ~2.5 and 1.7 Ga, providing insight into post-basin bombardment impact processes.</p><p>A third set of regolith breccias identified by Jerde et al. (1987, 1990), (the soil-like breccias), have no reported noble gas or exposure age information. Joy et al. (2011) inferred that these samples were likely consolidated into breccias in the last 2 Ga (based on their I<sub>s</sub>/FeO maturity being similar to the Apollo 16 soils). They, therefore, may extend the current archive of impact and regolith processes into the Eratosthenian and Copernican periods.</p><p>Whole-rock samples were laser step heated and the extracted gases were measured using a Thermo Scientific Helix-MC noble gas magnetic sector mass spectrometer. Preliminary analysis of our data shows these breccias are dominated by a solar wind composition component, with minor spallation and radiogenic contributions. The concentrations of evolved gases suggest the samples are more similar in terms of noble gas budget to the present day Apollo 16 soil samples (based on analysis using data collated by Curran et al. 2020), than the ancient gas-poor Apollo 16 regolith breccias (McKay et al. 1986). Thus, these noble gas data are consistent with the petrological characterisation and Is/FeO classification [5,6] of these breccias being comparable to present day Apollo 16 soil samples. Solar wind composition gas concentrations comparable to present day soil samples suggest these new breccias represent consolidated regolith of comparable maturity, perhaps suggesting these soil-like breccias were formed around the same time period as the ‘younger’ group.</p><p>References: [1] Curran, N.M., et al., 2020, PSS, 182, 104823. [2] Donohue, P.H., et al., 2013, 44<sup>th</sup> LPSC, A#2897.; [3] Fagan, A.L., et al., 2013, GCA, 106, 429-445.; [4] Fagan, A.L., et al., 2014, Earth Moon Planets, 112, 59–71.; [5] Jerde, E.A., et al., 1987, J. Geophys. Res., 92(B4), E526– E536.; [6] Jerde, E.A., et al., 1990, EPSL, 98(1), 90-108.; [7] Joy, K.H., et al., 2011, GCA, 75(22), 7208-7225.; [8] McKay, D.S., et al., (1986), J. Geophys. Res., 91(B4), 277– 303.</p>

Performance evaluation of a miniature magnetic sector mass spectrometer onboard a satellite in space

With the rapid development of space technology in China, it is urgent to use mass spectrometer to detect the space environment. In this work, a space miniature magnetic sector mass spectrometer is evaluated, which consists of three subsystems: (1) physical unit, (2) electric control unit, (3) and high voltage power. It has 90° magnetic sector-field analyzer with double trajectory, in which a trajectory measurement range is from 1 to 12 amu, the other range is from 6 to 90 amu.The mass spectrometer has two work models, one is used to measure space neutral gas when the filament of mass spectrometer ion source turned on, the other is used to measure space charged ions when the filament turned off. The absolute resolution of this device is less than 1 amu, the minimum detectable ion current is about 10−13 A, and the sensitivity is 10−6 A/Pa (N2). Its overall size is 170 mm × 165 mm × 170 mm, its weight is 4.5 kg, and its power consumption is 18 W. A series of environmental adaptability tests, including high and low temperature cycle, shock, vibration, thermal vacuum cycle, were carried out on the ground before launching, and sensitivity and peak position were also calibrated on the ground. In November 2012, the mass spectrometer was carried by an experimental satellite to 499 km sun synchronization and is still working right now. It successfully detected the atmosphere compositions both in the satellite orbit and gas-emitted from satellite, including O, He, 12CO2, 13CO2, H2, N2, O2, H2O, and so on.

Study of vaporization of LiI, LiI/C70, LiI/LiF/C70 from the Knudsen cell located into ionization chamber of the mass spectrometer

The vaporization of LiI, LiI/C70 and LiI/LIF/C70 were studied using a Knudsen cell located into ionization chamber of a magnetic sector mass spectrometer in a temperature range from 350 ?C to 850 ?C. ?s the ion species, LinI+ (n = 2, 3, 4, and 6) were identified from a mixture LiI/C70. While the clusters LinI+ and LinF+ (n = 2 - 6) were detected from a mixture LiI/LiF/C70. The intensities of LinI+ were higher than the emission of LinF+ cluster when the ratio of LiI to LiF was 2:1. By contrast, the emission of the LinF+ is favored when the ratio of LiI to LiF was 1:2. These results show that the vaporization of a mixture LiI/LIF/C70 from the Knudsen cell located into ionization chamber of the mass spectrometer represents an efficient and simple way to obtain and investigate clusters of the type LinX, X-F, I. In this work it has also been shown that the trend of the ln (Intensity, arbit. units) versus temperature for all LinI+ clusters before and after the melting point of LiI was not same. It suggested that the way of the formation of these clusters can be different due to changes in temperature.