Search

In this study, we developed four clinopyroxene (cpx) and five orthopyroxene (opx) samples as reference materials for SIMS water content analysis.

The neutron flux monitor is a critical part of the process of 40Ar/39Ar dating. We report a new protocol to prepare a neutron flux monitor from the sanidine contained within obsidian, a rock which has undergone rapid eruption and cooling on the surface.

The application of a 1012 Ω amplifier Faraday cup improved the secondary ion mass spectrometry analytical precision of the apatite Cl isotope by a factor of about two.

In this study, we developed two new SIMS (secondary ion mass spectrometry) analytical protocols to simultaneously measure oxygen–hydrogen (O–H) isotopic compositions and water content for hydrous geological samples. These two protocols involve the measurement of two sets of secondary ion contents: (1) 1H, 2H, 16O, 18O; and (2) 16O, 16O1H, 18O, 17O1H, 16O2H. Both measurements utilize a hybrid dynamic multi-collector system of CAMECA IMS 1280-HR, which benefits from both the static multi-collector mode and peak-hopping mono-collector mode. These new methods can simultaneously measure (with high-precision) the 18O/16O ratio in static multi-collector mode without trading off its analytical precision, and 1H/16O (or 16O1H/16O) and 2H/1H (or 16O2H/16O1H) ratios in conventional peak-hopping mono-collector mode. Three glass samples (LBS7H, LBS5H and LBS6H-) with known water contents and two apatite samples (Kovdor, Durango) with known oxygen–hydrogen isotopes and water content were measured to verify the protocols' reliability. The olivine crystal San Carlos with ∼1 ppmw water content was used for background monitoring. For the apatite samples, the external precision (spot-to-spot reproducibility) for δ18O and δD is better than 0.56‰ (2SD) and 54‰ (2SD), respectively. After eliminating the outlier (beyond 3SD error), the external precision of 16O1H/16O or 1H/16O ratio improves to 10.27% (2SD). For the glass samples, the water content calibration curves, which were constructed by comparison of the known water content with the SIMS measured 16O1H/16O or 1H/16O ratios, yielded good correlations. It is noteworthy that the apatite and glass samples can have a uniform water content calibration curve for protocol 1, but not for protocol 2, indicating different matrix effects for the two protocols.

In 40Ar/39Ar dating, 39ArK generated is dependent on irradiation conditions, and the accumulation fast neutron fluence is a critical parameter for 40Ar/39Ar dating. With technological advancement, especially in the ultra-low background and multicollector technology, the boundary conditions to choose irradiation conditions have been greatly improved. Based on the detected and processed signal, the maximum boundary condition of 40Ar*/39Ar can be up to 5750, meaning that very low 39Ar signals can yield considerable analytical accuracy. In this study, one biotite sample (ZBH-25) was irradiated for 4 hours to assess the modified irradiation conditions, and the high 40Ar*/39Ar ratio up to 4100 could yield ∼1% analytical uncertainty. This reveals that the new boundary condition is useful to choose fast neutron fluence, especially for very old or low K/Ca ratio samples.

Zircon water content is an important physicochemical parameter for many geological processes, yet its measurement by the secondary ion mass spectrometry (SIMS) technique is hampered by the lack of suitable reference materials and high water background, especially if large-geometry (LG)-SIMS is used. Here we have described a suite of newly developed reference materials for SIMS zircon water content analysis and a modified micro-analytical technique (using a CAMECA IMS 1280-HR SIMS) that can simultaneously measure the zircon water content and oxygen isotopes. A total of 20 natural zircon grains/sherds were analyzed via Fourier transform infrared spectroscopy (FTIR), among which 8 (with good water content result reproducibility) were further analyzed by SIMS. Before the SIMS analysis, FTIR analyzed sample blocks were mounted with a Sn-based alloy to minimize degassing and background water. As in routine SIMS oxygen isotope measurement, 16O− and 18O− were collected using two Faraday cups, and in addition 16O1H− was simultaneously measured using an electron multiplier. The measured 16O1H/6O ratio was converted into water content, using a calibration line established based on SIMS 16O1H−/16O− ratios vs. the FTIR water content. Both the internal and external precisions of corrected δ18O are

In this study, a high-precision secondary ion mass spectrometry (SIMS) zircon oxygen isotope ratio analytical protocol is described. The analysis is conducted using a Cameca IMS 1280-HR at the SIMS Laboratory of Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS). Four reference zircons (91,500, Qinghu, TEMORA 2 and Penglai) have been chosen to evaluate the reproducibility (precision) and accuracy. An identical protocol is used for the analyses, with unchanged instrumental parameters and with ion beam intensities kept as identical as possible. The Penglai zircon is used as an external reference material to calibrate the instrumental mass fractionation. The 91,500, Qinghu and TEMORA 2 zircons are used as the unknown samples, which yielded 10.15 ± 0.26‰ (2SD), 5.46 ± 0.24‰ (2SD) and 8.33 ± 0.29‰ (2SD), respectively, all consistent with the recommended values within error (2SD). A half-year long-term precision of 0.44‰ (2SD) is achieved using the Qinghu zircon as a monitoring sample for the routine measurement of zircon 18O/16O ratio, which demonstrates the reliability of this analytical protocol.

Secondary ion mass spectrometry (SIMS) has been applied to analyze a wide range of materials for earth science research due to its high sensitivity, high precision and capacity for in situ micro-analysis. This technique operates under ultra-high vacuum (UHV) conditions, especially for water content measurements on nominally anhydrous minerals (NAMs). However, UHV conditions are hard to achieve when using epoxy mounts, which degas readily during the vacuum processes. In this study, we developed a novel sample preparation method using a tin-based alloy instead of epoxy resin. Using a tin alloy mount coupled with an automatic liquid nitrogen refilling system, the results show that the vacuum conditions have been significantly improved from ∼1.2 × 10−8 mbar to ∼1.9 × 10−9 mbar. The background for mineral water content, measured with a CAMECA IMS 1280-HR SIMS installed at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS), is lowered to