Detrital zircon U-Pb ages, Hf isotopic constraints, and trace element analysis of Upper Cretaceous-Neogene sedimentary units in the Western Nepal Himalaya: Implications for provenance changes and India-Asia collision

摘要

The present study integrates detrital zircon U-Pb-Hf isotopic analysis from 13 sandstone samples from an Upper Cretaceous-Miocene sedimentary sequence in Nepal Himalaya to determine their provenance. These sequences constrain a shifting of provenance from south to north. The U-Pb ages from Upper Cretaceous-Palaeocene strata (Amile Formation) mainly cluster between similar to 1,860 and 1,400 Ma with a peak at similar to 1,630 Ma and an absence of grains younger than the Palaeoproterozoic (1,400 Ma) age. The detritus yielded positive detrital zircon epsilon(Hf) (t) values (as high as +10). However, the detrital zircon U-Pb ages from Eocene-Miocene sequence cluster at similar to 500-650, similar to 700-900, similar to 1,600-1,850, and similar to 2,500 Ma, and in addition, they have both positive and negative epsilon(Hf) (t) values (+11 to -25). This finding further elucidates that the detritus in the Amile Formation was entirely sourced from India, which changed following the time of the Bhainskati Formation deposition, to a mixture of both Asian and Indian affinities (the Himalayan region). This change in source region marks the possible time of the India-Asia collision during this transition phase, that is, Late Palaeocene-Earliest Eocene.