DID THE INDO-ASIAN COLLISION ALONE CREATE THE TIBETAN PLATEAU

It is widely believed that the Tibetan plateau is a late Cenozoic feat ure produced by the Indo-Asian collision. However, because Tibet was t he locus of continental accretion and subduction throughout the Mesozo ic, crustal thickening during that time may also have contributed to g rowth of the plateau. This portion of the geologic history was investi gated in a traverse through the central Lhasa block, southern Tibet. T ogether with earlier studies, our mapping and geochronological results show that the Lhasa block underwent little north-south shortening dur ing the Cenozoic. Rather, our mapping shows that similar to 60% crusta l shortening, perhaps due to the collision between the Lhasa and Qiang tang blocks, occurred during the Early Cretaceous. This observation im plies that a significant portion of southern Tibet was raised to perha ps 3-4 km elevation prior to the Indo-Asian collision.