Geology of Tibet

Geology; April 2000; v. 28; no. 4; p. 339-342; DOI: 10.1130/0091-7613(2000)28<339:HTOTTP>2.0.CO;2
© 2000 Geological Society of America

High times on the Tibetan Plateau: Paleoelevation of the Thakkhola graben, Nepal
Carmala N. Garzione1, David L. Dettman1, Jay Quade1, Peter G. DeCelles1 and Robert F. Butler1
1 Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

East-west extension in the Tibetan Plateau is generally assumed to have resulted from gravitational collapse following thickening and uplift. On the basis of this assumption, several studies have dated east-west extensional structures to determine when the plateau attained its current high elevation. However, independent estimates of elevation are needed to determine whether extension occurred before, during, or after the plateau achieved its current elevation. Because the isotopic composition of meteoric water decreases with increasing elevation, significant change in local elevation throughout the Thakkhola graben depositional history should be recorded by change in 18O values of fluvial and lacustrine carbonates. The 18O values of –16 to –23 of Thakkhola graben carbonates reflect meteoric water values similar to modern values and suggest that the southern Tibetan Plateau attained its current elevation prior to east-west extension. Initiation of Thakkhola graben extension is constrained between 10 and 11 Ma, based on magnetostratigraphy of the older Tetang Formation. The 13C values of soil carbonates suggest an age younger than 8 Ma for the base of the Thakkhola Formation.