Effects of accessory mineral inclusions and signal acquisition time on zircon U-Pb dating and trace element analysis results

doi:10.13745/j.esf.sf.2024.2.23

Abstract

Abstract:

In-situ zircon micro-area U-Pb dating and trace element analysis have become routine techniques in Earth sciences. However, the interpretation of zircon micro-area analysis results is influenced by various factors, including the selection of analysis points, instrument stability, and signal correction. Quantitatively understanding how these factors affect zircon micro-area analysis results is a critical prerequisite for accurately interpreting the geological significance of such data. This study focuses on zircons from the Late Triassic monzogranite porphyry intrusion in the Yemaquan iron-polymetallic deposit in Qinghai Province. LA-ICP-MS zircon in-situ U-Pb dating and trace element analysis were performed to evaluate the effects of accessory mineral inclusions and signal acquisition time on zircon micro-area analysis results. The findings indicate that although shorter signal acquisition times lead to larger errors in U-Pb dating, they do not significantly affect U-Pb ages or trace element analysis results. A comparison of analysis points with and without mineral inclusions shows that the presence of mineral inclusions also does not significantly interfere with dating results. However, if the selected zircon analysis location contains accessory mineral inclusions (e.g., apatite), the resulting data may display a false “light rare earth element enrichment” signature. This can lead to misinterpretations, such as incorrectly inferring magmatic oxygen fugacity characteristics. Therefore, it is crucial to first identify whether accessory mineral inclusions are present at the analysis location before conducting zircon micro-area analysis. Additionally, zircon data contaminated by mineral inclusions must be excluded prior to interpreting the geological significance of zircon trace element data.

Key words: LA-ICP-MS, zircon, U-Pb dating, accessory mineral inclusions, signal acquisition time

CLC Number:

P595
P597.3

HUANG Yu, ZHONG Shihua, LI Sanzhong, ZHAO Hong, XUE Zimeng, GUO Guanghui, LIU Jiaqing, NIU Jinghui. Effects of accessory mineral inclusions and signal acquisition time on zircon U-Pb dating and trace element analysis results[J]. Earth Science Frontiers, 2025, 32(1): 388-400.

Figures/Tables 12

Fig.1 Zircons with mineral-rich inclusions from the Yemaquan monzonite granite porphyry (a) and the corresponding zircon signal processing interface in the ICPMSDataCal software (b)

Fig.2 Geological map of Qimantage metallogenic belt. Modified after [21].

Fig.3 Strata histogram (a) and geological map (b) of the Yemaquan deposit. Modified after [21].

Fig.4 Photograph of the Yemaquan monzonite granite porphyry sample

Fig.5 Typical zircon CL images, transmitted light, and reflected light photographs from the Yemaquan monzonitic granite porphyry

Table 1 U-Pb isotopic analysis and age results of zircon from Yemaquan monzonite granite porphyry (signal acquisition time 45s)

Fig.6 When analyzing apatite in the digital signal acquisition window of the ICPMSDataCal software, the curves of certain elements exhibit a bulging rise.

Fig.7 Weighted average age diagrams (a-d) and U-Pb isotope concordia diagrams (e-h) of zircon from the Yemaquan monzonitic granite porphyry under different signal acquisition times.

Fig.8 REE Distribution patterns of zircon from the Yemaquan monzonitic granite porphyry under different signal acquisition times, standardized to chondrite (normalization values based on [30])

Fig.9 (Th+U)-(La/Gd)N diagram of zircons from the Yemaquan monzonitic granite porphyry

Fig.10 Eu/Eu*-Ce/Ce* diagram of zircons from the Yemaquan monzonitic granite porphyry under different signal acquisition times

Fig.11 Temperature-log f O 2 diagrams (a-d) and temperature-ΔFMQ diagrams (e-h) of zircons from the Yemaquan monzonitic granite porphyry under different signal acquisition times.

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