Dinesh Raj Sharma and Naresh Kazi Tamrakar*

Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal (*Corresponding Author, E-mail: naresh.tamrakar@cdgl.tu.edu.np)

Abstract

Petrographic investigations of quartzites from four distinct units Fagfog, Dunga, Pandrang, and Chisapani Quartzites within the Central Nepal Lesser Himalaya were undertaken to characterize composition, texture and microstructures. The Fagfog and Dunga Quartzite respectively belong to the Lower Nawakot Group and the Upper Nawakot Group, whereas the Pandrang and the Chisapani Quartzites belong to the Bhimphedi Group of the Kathmandu Complex, and occur in ascending order. The Kathmandu Complex (allochthonous sequence) thrusts over the Nawakot Complex (autochthonous sequence) along the Mahabharat Thrust. Microscopic techniques, including polarized light microscopy and point-count analysis were employed to reveal significant petrographic variations among the studied units. The Fagfog Quartzite, comprising 89-94% quartz with minor muscovite and biotite, exhibits a massive microstructure characterized by subequant to elongate grains and evidence of low-temperature deformation dominated by subgrain rotation, indicating a sedimentary protolith with minimal metamorphic overprint. The Dunga Quartzite, containing 85-93% quartz, displays both banded and massive textures with equigranular to porphyroclastic grains, reflecting mixed recrystallization mechanisms such as subgrain rotation and grain boundary migration that suggest moderate deformation. In contrast, the Pandrang Quartzite, with quartz content ranging from 83-95%, is characterized by polygonal grains indicative of high-temperature grain boundary migration, and whereas the Chisapani Quartzite, exhibiting 85-91% quartz, is marked by ribbon-like quartz fabrics formed under intense strain at high temperatures. These petrographic differences delineate an inverted metamorphic gradient, underscoring the region’s complex tectonic evolution and providing insights into lithostratigraphic correlations and potential applications as ballast material for infrastructure development. This study not only delineates quartzite petrographic variations but also enhances understanding of the regional tectono-metamorphic framework. Analysis of microstructures and mineralogical data supports inferences regarding deformation-related microfabric development and prevailing metamorphic conditions, offering valuable insights for geological research and engineering applications

Keywords: Quartzite, Petrography, Deformation, Metamorphism, Lesser Himalaya