Was there a Greater Asia before India-Asia collision?

Previous paleomagnetic studies in central Asia have suggested some 1500 km of intracontinental shortening occurred north of the India-Asia suture. This suggests the existence of a "Greater Asia" that was about one and half times the size of the present Tibetan plateau and the same extent as Greater India. However, recent studies indicate that the paleomagnetic directions carried by continental red beds may have a significant bias toward shallow inclinations. If this is true for the red beds in Tibet, it could lead to an overestimate for the southern extension of Greater Asia and hence an older India-Asia collision age. To test the accuracy of paleomagnetic directions, we have collected samples from Late Cretaceous red beds and lava flows and Eocene tuffs from the Linzhou basin, Lhasa block. Our laboratory work successfully isolated characteristic remanent directions from the red beds and volcanic samples. Preliminary analysis of systematic demagnetization data appears that the paleomagnetic inclinations carried by the red beds are significantly shallower than those from the lava flows. Therefore, "Greater Asia" could be much smaller than previously thought. We will report detailed paleomagnetic results and elongation/inclination analysis for the red beds directions, and discuss their implications for India-Asia collision.