Buckling of the lithosphere in western Himalaya: Constraints from gravity and topography data

The deformation of the lithosphere in western Himalaya and Karakoram is ana lyzed by correlating Bouguer gravity anomalies and topographic heights samp led along profiles in the direction of the Indo-Asian collision. The spectr al features of the coherence, linear admittance, and correlation coefficien ts between topography and deformation at depth support the hypothesis that the flexural mode of Lithospheric deformation is complemented by a folding mode, with typical wavelengths concentrated in bands centered at 250 and 12 0 km. When combined with realistic models of a theologically stratified lit hosphere with two strong layers (upper crust and upper mantle) sandwiching a weak, very ductile layer (the lower crust), the data are consistent with a model of response to horizontal deformation in which a coupled, biharmoni c folding instability develops: The lithosphere as a whole warps with the l onger wavelengths and the upper layer alone also with the shorter wavelengt hs. Major faults, such as the Main Boundary Thrust, or the Main Karakoram T hrust and the computed folds of the upper layer are phased, as if there wer e a causal relationship between the position of the faults and the zones of highest strain in the crust.