| Abstract: | Detachment tectonics, in which the subducting basement is not internally affected by thrusting; and a steady state system, in which the pattern of deformation and topography are invariant, uplift is balanced by erosion and the material can experience subsequent “phases” of deformation by migrating through the system, are proposed to be the fundamental mechanisms of convergence at the Himalayan arc. Both surface and subsurface data are more consistent with these concepts than with more familiar concepts widely used in current models: intracrustal thrusting and evolutionary tectonics, where superimposed phases of deformation are interpreted as distinct phases. The belt of intermediate-magnitude thrust-earthquakes, the topographic front at the High Himalaya and the Main Central Thrust (MCT) are associated with the same fundamental element, the basement thrust front (BTF), which traces a small circle in the central portion of the Himalayan arc. Fault plane solutions indicate thrusting in the radial direction of this arc. This radial convergence at the BTF implies that Tibet is extending laterally at a rate similar to the rate of convergence across the BTF. This extension cannot be unidirectional and must be parallel to the BTF, if the circular shape of the BTF is invariant. |
