Impact and Correction of Analytical Positioning on Accuracy of Zircon U-Pb Dating by SIMS.

Yu Liu,Xian-Hua Li,Xiao-Xiao Ling,Jiao Li,Guo-Qiang Tang,Qiu-Li Li

doi:10.3389/fchem.2020.605646

Abstract

Secondary ion mass spectrometry (SIMS) is one of the most important analytical tools for geochronology, especially for zircon U-Pb dating. Due to its advantages in spatial resolution and analytical precision, SIMS is the preferred option for multi-spot analyses on single zircon grain with complex structures. However, whether or how much the relative positions of multiple analytical spots on one zircon grain affect the U-Pb age accuracy is an important issue that has been neglected by most researchers. In this study, we carried out a series of investigation on the influence of relative analytical position during zircon U-Pb age analyses, using Cameca IMS 1280-HR instrument. The results demonstrated a significant influence on the second spot, with apparent U-Pb age deviation as high as around 10% especially on the left and right side with overlap in the raster area. Nevertheless, a linear correlation between a secondary ion centering parameter (DTCA-X) and age deviation in percentage terms was found, and a calibration method was established to correct this position effect. Four zircon standards (91500, M257, TEMORA-2, and Plešovice) were measured to prove the reliability of the established procedure. The original U-Pb apparent data show inconsistent deviation on four directions relative to the datum, while the final U-Pb age results is calibrated to be consistent with their recommended values, within uncertainties of ~1%. This work calls for re-examination for the previous SIMS U-Pb dating results on core-rim dating strategy, and provides a calibration protocol to correct the relative position effect.

Highlights

Secondary ion mass spectrometry (SIMS) is widely and routinely used in U-Pb dating of zircon and other accessory minerals
The results of session 1 demonstrated that there is an obvious positioning effect during SIMS analysis, which has a significant impact on the 238U-206Pb apparent age results, especially on the X direction
Results of Session 3 After the routine U-Pb fractionation correction and common Pb correction (Li et al, 2009), the U-Pb ages of all spots in session 3 are plotted in Figure 4, and the detailed results are listed in Supplementary Table 3

Summary

Introduction

Secondary ion mass spectrometry (SIMS) is widely and routinely used in U-Pb dating of zircon and other accessory minerals. It can achieve a lateral resolution of 2–30 μm and a depth resolution of 1–2 μm, which makes it the first choice for in situ high spatial resolution zircon U-Pb dating. By using SIMS, multiple U-Pb dating analyses on different crystal domains of single zircon grain were routinely carried out to reveal its growth processes, and the corresponding geological evolution history (e.g., Hermann and Rubatto, 2003; Whitehouse and Platt, 2003; Zhang et al, 2005; Tang et al, 2008; Qian et al, 2013). The instrument developers were aware of this potential influence (e.g., Ickert et al, 2008), no quantitative study has been reported on this issue.

Methods

Results

Conclusion