STRATIGRAPHIC EVIDENCE FOR AN EARLY COLLISION BETWEEN NORTHWEST INDIAAND ASIA

THE collision of India with Asia(1) had a profound influence on late C retaceous and Cenozoic oceanography(2), climate(3), faunal extinctions (4) and the motion of at least some of the Earth's lithospheric plates (5). As the collision ended a period of rapid Indo-Asian convergence, a precise knowledge of its timing (when the crust of the neo-Tethys oc ean was completely subducted(7), at some point along the plate boundar y) is important for understanding its wider consequences, But current estimates of the collision age range from 65 to 38 Myr before present( 6,8-11), Here we report the results of extensive biostratigraphic anal yses from Waziristan and Kurram in northwest Pakistan, which show that accretionary-prism and trench strata Were first thrust onto the north west Indian passive margin after 66 Myr but before 55.5 Myr. After thi s time, volcanic-are fragments, the accretionary prism, trench materia l and imbricates of the north Indian slope were raised to shallow wate r depths and overlapped by upper Palaeocene shallow-water carbonates a nd shales(12-14), indicative of post-collision thrusting in this regio n. Finally, both the suture and the Indian craton were overlapped by c ontinuous unconformable upper Lower Eocene shallow-marine strata, demo nstrating that suturing was complete by 49 Myr.