Features of the Crust--Mantle Structure of Himalayas--Tibet: A Comparison with Seismic Traverses of Alpine, Pyrenean and Variscan Orogenic Belts

Seismic data able to resolve the crustal structure are limited in quantity and quality with respect to the size and complexity of Tibet--Himalayas. They may be interpreted as indicating a strong heterogeneity: lack of continuity of even major interfaces across strike, defining different crustal blocks, but also lack of continuity of surface tectonic features down through the whole lithosphere. A thickening by imbrication of both the upper crustal and the lower crust--upper mantle levels is suggested. Indications from recent high-resolution surveys in other domains of thickened crust are also of a less smooth geometry of structures and depth than intuitively considered.