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<p>The high-K granites in the southeastern part of the Bundelkhand Craton (BC) are classified as medium-grained granite (MG) and porphyritic granite (PG) based on the grain size and texture. Field evidence including interfingering relationships and the presence of enclaves inside one another suggest that both&#xa0;felsic magmas interacted during the magma emplacement process. Their mineralogical composition remains similar i.e. K-feldspar, plagioclase feldspar, quartz, biotite, and hornblende being the primary rock-forming minerals in both granites, though PG tends to be relatively richer in hornblende than MG. The mineral chemistry connotes that the amphiboles of both the granites are of igneous origin and corresponds to edenite while the biotites are Mg-rich and comparable with that of sub-alkaline to calcalkaline granite suites. Geochemically, both the granites are K-rich, magnesian, calc-alkalic to alkali-calcic, and metaluminous to weakly peraluminous in nature. Such I-type granite with relatively low Al-content and high ferromagnesian oxides exhibit a high K<sub>2</sub>O/Na<sub>2</sub>O ratio (average of ~ 1.83), similar to S-type granite. However, the enrichment of biotite, presence of magmatic epidote, absence of primary muscovite, and major-oxide composition supports a hybrid I-type nature for the Bundelkhand Granite (BuG). The trace element signatures further clarify the magma source. The low Ce/Pb and Nb/U ratios, alongside high Th/U ratios in the samples, suggest a significant crustal origin as marked by enrichment in LREE and LILEs (e.g., K, Rb, Pb) and depletion in HREE, Nb, and Ta- features typical of lower crustal rocks. Conversely, the presence of mafic microgranular enclaves (MMEs) and high Mg<sup>#</sup> values indicate a notable mantle contribution as well. Therefore, the petrological and geochemical evidence supports a model in which the high-K granites from the southeastern part of Bundelkahnd Craton (BC) originated through the interaction and mixing of crust-mantle derived magmas. This magmatic evolution likely occurred in a tectonic framework that transitioned from arc-related subduction to continental collision, providing the most compelling explanation for the genesis of these hybrid granites.</p>

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High-K granites from the bundelkhand craton: petrogenesis and geodynamic implication during the NeoArchaean time

  • 期刊论文

  • 发表日期：

    2025年7月29日

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  • Saheli Sanyal,
  • Arnab Sain,
  • Atul Kumar Rastogi,
  • Gatikrishna Sahoo,
  • Dipak Hazra

摘要

The high-K granites in the southeastern part of the Bundelkhand Craton (BC) are classified as medium-grained granite (MG) and porphyritic granite (PG) based on the grain size and texture. Field evidence including interfingering relationships and the presence of enclaves inside one another suggest that both felsic magmas interacted during the magma emplacement process. Their mineralogical composition remains similar i.e. K-feldspar, plagioclase feldspar, quartz, biotite, and hornblende being the primary rock-forming minerals in both granites, though PG tends to be relatively richer in hornblende than MG. The mineral chemistry connotes that the amphiboles of both the granites are of igneous origin and corresponds to edenite while the biotites are Mg-rich and comparable with that of sub-alkaline to calcalkaline granite suites. Geochemically, both the granites are K-rich, magnesian, calc-alkalic to alkali-calcic, and metaluminous to weakly peraluminous in nature. Such I-type granite with relatively low Al-content and high ferromagnesian oxides exhibit a high K2O/Na2O ratio (average of ~ 1.83), similar to S-type granite. However, the enrichment of biotite, presence of magmatic epidote, absence of primary muscovite, and major-oxide composition supports a hybrid I-type nature for the Bundelkhand Granite (BuG). The trace element signatures further clarify the magma source. The low Ce/Pb and Nb/U ratios, alongside high Th/U ratios in the samples, suggest a significant crustal origin as marked by enrichment in LREE and LILEs (e.g., K, Rb, Pb) and depletion in HREE, Nb, and Ta- features typical of lower crustal rocks. Conversely, the presence of mafic microgranular enclaves (MMEs) and high Mg# values indicate a notable mantle contribution as well. Therefore, the petrological and geochemical evidence supports a model in which the high-K granites from the southeastern part of Bundelkahnd Craton (BC) originated through the interaction and mixing of crust-mantle derived magmas. This magmatic evolution likely occurred in a tectonic framework that transitioned from arc-related subduction to continental collision, providing the most compelling explanation for the genesis of these hybrid granites.