TIMING OF TIBETAN UPLIFT CONSTRAINED BY ANALYSIS OF VOLCANIC-ROCKS

THE Tibetan plateau has had a central role in the development of recen t models for the mechanics of mountain belts1,2 and Cenozoic global cl imate change3. The present elevation and extensional deformation of th e plateau probably result from uplift owing to convective thinning of the underlying lithospheric mantle1,2. An age for the uplift would pro vide a valuable constraint on these models; but because recently propo sed indicators of uplift are all climate-dependent, they are equivocal , possibly reflecting global cooling rather than regional uplift4. Her e we present new geochemical data on post-mid-Miocene lavas from the p lateau, which show that the lavas were derived from the lithospheric m antle. Simple thermal arguments indicate that the generation of such m agmas also necessitates thinning of the lithospheric mantle. Thus volc anism is coincident with uplift, providing a climate-independent means of dating the onset of uplift. Dating by the laser Ar-40/Ar-39 techni que places the beginning of this volcanism, and therefore the time of uplift of the Tibetan plateau, at 13 Myr ago.