Predicting paleoelevation of Tibet and the Himalaya from δ 18O vs. altitude gradients in meteoric water across the Nepal Himalaya
The δ 18O value of meteoric water varies with elevation, providing a means to reconstruct paleoelevation if the δ 18O values of paleowater are known. In this study, we determined the δ 18O values of water (δ 18O mw) from small tributaries along the Seti River and Kali Gandaki in the Nepal Himalaya. We found that δ 18O mw values decrease with increasing altitude for both transects. δ 18O mw vs. altitude along the Kali Gandaki in west-central Nepal fit a second order polynomial curve, consistent with increasing depletion of 18O with increasing elevation, as predicted by a Rayleigh-type fractionation process. This modern δ 18O mw vs. altitude relationship can be used to constrain paleoelevation from the δ 18O values of Miocene-Pliocene carbonate (δ 18O c) deposited in the Thakkhola graben in the southern Tibetan Plateau. Paleoelevations of 3800±480 m to 5900±350 are predicted for the older Tetang Formation and 4500±430 m to 6300±330 m for the younger Thakkhola Formation. These paleoelevation estimates suggest that by ∼11 Ma the southern Tibetan Plateau was at a similar elevation to modern.