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<p>New geochemical and geochronological data are presented for a suite of metavolcanic rocks of the Kudrekonda Formation, Shimoga Greenstone Belt, western Dharwar Craton. Earlier studies assigned the Kudrekonda Formation to the Mesoarchean Bababudan Group, while the Medur and Daginakatte Formations to the Neoarchean Lower Chitradurga Group. Precise age data on the metavolcanic rocks of the Kudrekonda Formation are needed to understand their temporal relationship with those of the Daginakatte and Medur Formations and Bababudan and Chitradurga greenstone belts. We report U–Pb ages, determined using LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry), of 2585.2 ± 18 Ma (MSWD = 1.9), 2608.2 ± 11.0 Ma (MSWD = 3.8) and 2586.7 ± 16.0 Ma (MSWD = 0.66) for basalt, andesite and dacite of Kudrekonda Formation, respectively. These ages determined are indistinguishable from the earlier reported ages of the Medur and Daginakatte Formations; thus, they possibly were emplaced in basins developed within a short period around the Honnali Dome. Metavolcanic rocks show enrichment of LREE and Th with prominent negative Nb and Sr anomaly, indicating their magmas formed in an island arc tectonic setting by partial melting of mixed lithosphere–asthenospheric mantle sources. These sources were metasomatized with older crustal components as inferred from initial <i>ε</i>Hf values of the zircons (+1.8 to +9.1) that fall below the depleted mantle growth curve and above the field for enriched continental crustal rocks.</p>

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U–Pb ages, Lu–Hf systematics on zircons and geochemistry of metavolcanic rocks from the Shimoga Greenstone Belt: Evidence for rapid growth of volcano-sedimentary basin during Neoarchean

  • 期刊论文

  • 发表日期：

    2025年4月26日

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  • S Nanila,
  • S Balakrishnan,
  • M Rajamanickam,
  • Ushasi Daripa,
  • Arathy Ravindran,
  • Marcel Guillong,
  • J K Tomson

摘要

New geochemical and geochronological data are presented for a suite of metavolcanic rocks of the Kudrekonda Formation, Shimoga Greenstone Belt, western Dharwar Craton. Earlier studies assigned the Kudrekonda Formation to the Mesoarchean Bababudan Group, while the Medur and Daginakatte Formations to the Neoarchean Lower Chitradurga Group. Precise age data on the metavolcanic rocks of the Kudrekonda Formation are needed to understand their temporal relationship with those of the Daginakatte and Medur Formations and Bababudan and Chitradurga greenstone belts. We report U–Pb ages, determined using LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry), of 2585.2 ± 18 Ma (MSWD = 1.9), 2608.2 ± 11.0 Ma (MSWD = 3.8) and 2586.7 ± 16.0 Ma (MSWD = 0.66) for basalt, andesite and dacite of Kudrekonda Formation, respectively. These ages determined are indistinguishable from the earlier reported ages of the Medur and Daginakatte Formations; thus, they possibly were emplaced in basins developed within a short period around the Honnali Dome. Metavolcanic rocks show enrichment of LREE and Th with prominent negative Nb and Sr anomaly, indicating their magmas formed in an island arc tectonic setting by partial melting of mixed lithosphere–asthenospheric mantle sources. These sources were metasomatized with older crustal components as inferred from initial εHf values of the zircons (+1.8 to +9.1) that fall below the depleted mantle growth curve and above the field for enriched continental crustal rocks.