Geochemistry of the Gondwana sequence in the eastern Nepal Lesser Himalaya: Implications for provenance

Abstract: The Barahakshetra–Ranitar area of eastern Nepal preserves a succession of Lower to Upper Gondwana sediments within the extra-peninsular Lesser Himalaya, yet detailed geochemical investigations of these sediments remain limited. The succession comprises the Permo-Carboniferous Kokaha Diamictite, the Permian Tamrang Formation with Baraha Volcanics, and the Late Cretaceous to Early Paleogene Sapt Koshi Formation. Provenance has been assessed through petrographic observations and whole-rock geochemical analyses (XRF and ICP-MS). Major oxide data show high SiO₂ contents (44.8–80.9 wt%) with variable Fe₂O₃ and K₂O, while weathering indices (CIA 64–77, PIA 82–93, CIW 82–99) indicate moderate to intense chemical weathering in the source areas, except for one tuff sample from the Baraha Volcanics that records limited alteration. Trace element and REE signatures, including LREE enrichment, negative Eu anomalies, and elevated Zr/Sc and Th/Sc ratios, point to a felsic-dominated continental provenance. These characteristics are consistent with derivation from Archean to Proterozoic granitoid provinces of the northern Indian craton, particularly the Bundelkhand and Chotanagpur Granite–Gneiss complexes. Key Words: Gondwana sequence; Barahakshetra–Ranitar; provenance; geochemistry; Indian craton