Petrographic Study, Mode of Occurrence and Tectonic Setting of the Palung Granite, Lesser Himalaya, Central Nepal

Abstract

The Palung granite located in Central Nepal exhibits significant mineralogical, textural, and structural variations. Detailed field mapping, petrographic analysis, and modal mineralogy and their composition helped to identify five distinct zones in this pluton, reflecting progressive magmatic differentiation and tectonic overprinting. The more deformed southern part compared to the northern part shows gneissic texture. Geochemical data plotted on the tectonic discrimination diagrams show a consistent and coherent pattern. The K₂O-SiO₂ plot shows the potassium enrichment typical of evolved felsic magmas, suggesting significant crustal involvement during magma generation. The sample cluster trends in the Al₂O₃-SiO₂ diagram show felsic to intermediate crustal sources rather than the purely mantle-derived magmas. The fractionated felsic granites are observed in the FeOᵗ/(FeOᵗ + MgO) versus SiO₂ diagram. Likewise, F/FM versus M/AFM and F/CF versus C/ACF helped to identify that the Palung granite mainly originated in the continental collision (CCG). The granite samples plotted in the A/CNK versus A/NK diagram show that most of the samples are weakly to moderately peraluminous, with A/CNK values commonly exceeding 1.0, belonging to metasedimentary or felsic crustal source materials.  Petrological and chemical evidence, and field study suggest that the Palung granite crystallized at moderate to shallow crustal levels, likely within the upper to mid-crustal depth.