RECONCILING CONTRADICTIONS IN KINEMATIC RECONSTRUCTIONS OF GREATER INDIA AND TIBET, AND THE GEODYNAMICS OF PLATEAU RISE AND PLATE MOTION CHANGE

At the heart of a successful geodynamic or paleoclimatic analysis lies a plate and orogen- kinematic or paleogeographic reconstruction. I will present a kinematic reconstruction of Greater India and Tibet, using a reconstruction protocol based on the following datasets: (1) marine magnetic anomalies and fracture zones in the modern oceans; (2) structural geology and paleomagnetic rotations and (3) paleolatitude estimates from deformed belts, and (4) seismic tomographic constraints on subducted lithosphere remnants. Data from e.g., sediment provenance, volcanism, or biogeography do not quantify motions and are best interpreted in the light of kinematic reconstructions rather than vice versa. This protocol constrains a width of continental Greater India prior to ~120 Ma of ~800 km, and show 1000-1200 km of Cenozoic intra-Asian shortening, not supporting or requiring significantly greater values. These restorations combined with well-constrained India-Asia convergence rates would predict an Early Miocene Tibetan Himalaya-Lhasa collision, which is clearly inconsistent with sediment provenance and metamorphic arguments for 58±2 Ma collision. Such early collision then necessitates the opening of an up to 2500 km wide Greater India ocean Basin since 120 Ma, consistent with volcanic evidence for Early Cretaceous rifting along the Himalaya. The GIB subducted in the Eo-Oligocene without rock accretion, as is default in circum-Pacific subduction zones such as below the Andes. Eocene sediments on India argued to derive from the Tibetan Himalaya are then more likely derived from the Paleogene obduction-induced orogen of Pakistan and Afghanistan unrelated to the India-Asia collision. Using this kinematic restoration, I explain the delay between 58 Ma collision and a 50 Ma onset of dramatic Indian plate motion deceleration by the resistance of the GIB against lower mantle subduction. Subsequent filling of the upper mantle led to slab overturning and advance demonstrated in seismic tomography, inducing oceanic flat slab subduction, Tibetan plateau growth and arrest of arc volcanism. Associated increase in frictional plate contact area, slab bending, and upper plate thickening likely triggered the Indian deceleration. Continental collision only significantly contributed to Tibetan evolution since ~30-20 Ma.