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<p><i>In-situ</i> isotopic and elemental analysis using laser ablation coupled with high-resolution magnetic sector inductively coupled plasma mass spectrometer (LA-HR-ICP-MS) is a popular technique in geosciences with major applications in U–Pb geochronology. When compared to other mass spectrometric techniques available for <i>in-situ</i> analyses, ease of analysis along with low maintenance and running costs, as well as the large data throughput, are the major advantages of LA-HR-ICP-MS. This study presents an analytical protocol developed for high precision U–Pb isotopic measurement in zircon using NWR 213 Nd YAG laser ablation system coupled with a Nu AttoM<sup>®</sup> HR-ICP-MS. Experiments were conducted on different laser repetition rates and fluences to explore the optimum setting with minimum analytical uncertainties. The calibration and optimization of the method were done using the well-characterized reference zircon 91500, Mud Tank, BR-266 and Plešovice. The Mud Tank, BR-266, and Plešovice reference standards were used for secondary calibration to assess the data quality and robustness of the method. We obtained precise isotopic ratios and concordant ages for these reference materials at spot sizes of 40 and 25 µm, validating the robustness of the U–Pb isotope measurement protocol developed in our laboratory. The zircon&#xa0;reference materials resulted in ages of 733 ± 4 Ma (Mud Tank), 561 ± 4 Ma (BR 266), 339 ± 2 Ma (Plešovice) on 40 µm spot ablation, and 737 ± 6 Ma, 571 ± 5 Ma, 338 ± 2 Ma, respectively, on 25 µm spot ablation. The obtained isotopic ratios and corresponding ages are in good agreement with their recommended values. To demonstrate the potential of our analytical protocol, we analyzed detrital zircon grains from the Gulcheru Formation of the Cuddapah Basin of southern India to understand the timing of basin formation and sediment provenance. U–Pb ages from our study reveals ten concordant age populations corresponding to 3516 ± 19 Ma, 3198 ± 22 Ma, 3001 ± 26 Ma, 2830 ± 26 Ma, 2690 ± 13 Ma, 2573 ± 9 Ma, 2518 ± 18 Ma, 2469 ± 24 Ma, 2140 ± 20 Ma, and 2066 ± 20 Ma. The Archean ages overlap with major episodes of felsic magmatism in the adjacent Dharwar Craton and hence can be considered sediment provenance. The youngest detrital zircon age population of <i>c</i>. 2066 Ma is interpreted as the maximum depositional age (MDA) of sediments of the Gulcheru Formation. The new geochronological data suggest commencement of sedimentation in the Cuddapah Basin around <i>c</i>. 2066 Ma.</p>

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Protocol for the in-situ U–Pb dating of zircon with high sample throughput and spatial resolution using LA-HR-ICP-MS: A case study on detrital zircon from the Cuddapah Basin

  • 期刊论文

  • 发表日期：

    2025年9月30日

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  • Sameer Ranjan,
  • Ajay Dev Asokan,
  • M Ram Mohan,
  • M Satyanarayanan,
  • D Srinivasa Sarma

摘要

In-situ isotopic and elemental analysis using laser ablation coupled with high-resolution magnetic sector inductively coupled plasma mass spectrometer (LA-HR-ICP-MS) is a popular technique in geosciences with major applications in U–Pb geochronology. When compared to other mass spectrometric techniques available for in-situ analyses, ease of analysis along with low maintenance and running costs, as well as the large data throughput, are the major advantages of LA-HR-ICP-MS. This study presents an analytical protocol developed for high precision U–Pb isotopic measurement in zircon using NWR 213 Nd YAG laser ablation system coupled with a Nu AttoM® HR-ICP-MS. Experiments were conducted on different laser repetition rates and fluences to explore the optimum setting with minimum analytical uncertainties. The calibration and optimization of the method were done using the well-characterized reference zircon 91500, Mud Tank, BR-266 and Plešovice. The Mud Tank, BR-266, and Plešovice reference standards were used for secondary calibration to assess the data quality and robustness of the method. We obtained precise isotopic ratios and concordant ages for these reference materials at spot sizes of 40 and 25 µm, validating the robustness of the U–Pb isotope measurement protocol developed in our laboratory. The zircon reference materials resulted in ages of 733 ± 4 Ma (Mud Tank), 561 ± 4 Ma (BR 266), 339 ± 2 Ma (Plešovice) on 40 µm spot ablation, and 737 ± 6 Ma, 571 ± 5 Ma, 338 ± 2 Ma, respectively, on 25 µm spot ablation. The obtained isotopic ratios and corresponding ages are in good agreement with their recommended values. To demonstrate the potential of our analytical protocol, we analyzed detrital zircon grains from the Gulcheru Formation of the Cuddapah Basin of southern India to understand the timing of basin formation and sediment provenance. U–Pb ages from our study reveals ten concordant age populations corresponding to 3516 ± 19 Ma, 3198 ± 22 Ma, 3001 ± 26 Ma, 2830 ± 26 Ma, 2690 ± 13 Ma, 2573 ± 9 Ma, 2518 ± 18 Ma, 2469 ± 24 Ma, 2140 ± 20 Ma, and 2066 ± 20 Ma. The Archean ages overlap with major episodes of felsic magmatism in the adjacent Dharwar Craton and hence can be considered sediment provenance. The youngest detrital zircon age population of c. 2066 Ma is interpreted as the maximum depositional age (MDA) of sediments of the Gulcheru Formation. The new geochronological data suggest commencement of sedimentation in the Cuddapah Basin around c. 2066 Ma.