Elemental and Sr-Nd isotopic geochemistry of Mesoproterozoic sedimentary successions from NE Lesser Himalaya, northern India: Implications for Proterozoic climate and tectonics

The sedimentation history of northeastern Himalayan Proterozoic basins is poorly known. In the current study, we examine major, trace, rare earth elements (REEs) and Sr-Nd isotope geochemistry of pelites and quartzites from Mesoproterozoic metasedimenatary sequences of Bomdila and Rupa Groups, NE Himalaya in order to understand provenance, tectonic setting and paleoweathering conditions of deposition. The salient geochemical parameters, such as, high SiO2 and Al2O3 concentrations, relatively low MgO values, typical enrichment of immobile incompatible elements (Al2O3/TiO2 = 32.2, Th/Sc = 2.1), fractionated REE patterns (La/Yb-n = 28) and a strong negative europium anomaly (Eu/Eu* = 0.3-0.7) indicate dominant felsic source for Bomdila sediments. Bomdila sediments show significantly radiogenic epsilon Nd-0.95Ga values ( -10.25 to - 17.90, avg. - 15.24) compared to Bundelkhand craton (avg. - 26) and Singhbhum craton (avg. - 30) and yield much younger Tom ages (2.3-2.7 Ga) compared to Archean Bundelkhand (3.2-3.5 Ga) and Singhbhum cratons (3.4-3.9 Ga). These results clearly rule out any significant detritus contribution from old cratonic sources. epsilon Nd and T-DM data of Mesoprterozoic Bomdila sediments envelop the signature of Lower Proterozoic Inner Lesser Himalayan (ILH) terrane. Prominent U-Pb age peaks at 1702, 1651, similar to 1400, 1248 and 1118 Ma in detrital zircons indicate major contribution from Late Paleoroterozoic to Late Mesoproterozic sources. However, initial Nd isotope ratios and T-DM do not favour any juvenile inputs. We argue that ILH source terrain may have been extensively reworked during Late Paleoroterozoic to Late Mesoproterozic time and could have been part of a long lived orogenic belt.. Severe depletion of Ca, Na and Sr in Bomdila sediments indicate intense chemical weathering of the source region, and can be attributed to warm and humid climatic conditions, a conclusion which is consistent with the CO2-rich atmosphere during Mesoproterozoic period.