Predicting paleoelevation of Tibet and the Himalaya from δ18O vs. altitude gradients in meteoric water across the Nepal Himalaya

The delta O-18 value of meteoric water varies with elevation, providing a means to reconstruct paleoelevation if the delta O-18 values of paleowater are known. In this study, we determined the delta O-18 values of water (delta O-18(mw)) from small tributaries along the Seti River and Kali Gandaki in the Nepal Himalaya. We found that delta O-18(mw) values decrease with increasing altitude for both transects. delta O-18(mw) vs. altitude along the Kali Gandaki in west-central Nepal fit a second order polynomial curve, consistent with increasing depletion of O-18 with increasing elevation, as predicted by a Rayleigh-type fractionation process. This modern delta O-18(mw) vs, altitude relationship can be used to constrain paleoelevation from the delta O-18 values of RiIiocene-Pliocene carbonate (delta O-18(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 similar to 11 Ma the southern Tibetan Plateau was at a similar elevation to modern. (C) 2000 Elsevier Science B.V. All rights reserved.