Role of the Asthenosphere in Transfer and Deformation of the Lithosphere: The Ethiopian-Afar Superplume and the Alpine-Himalayan Belt

摘要

Seismic tomographic data showing the mantle structure of the Ethiopian-Afar superplume and various segments of the Alpine-Himalayan Orogenic Belt and their relationships with the adjacent mega-structures of the Earth are presented. These data and their correlation with the geological evidence lead to the conclusion that lateral flows of mantle material are crucial for the evolution of the Tethys and its closure in the Cenozoic with transformation into an orogenic belt. The lateral flow of hot upper mantle asthenospheric matter spreading from the stationary superplume extending in the meridional direction (in present-day coordinates) was responsible for the accretion of the fragments torn away from Gondwana to Eurasia and for the development of subduction at the northeastern flank of the Tethys. The characteristic upper mantle structure of cold slabs passing into nearly horizontal lenses with elevated seismic wave velocity in the lowermost upper mantle is currently retained in the Indonesian segment of the orogenic belt. In the northwestern segments of this belt, a hot asthenospheric flow reached its northern margin after closure of the Tethys and onset of collision, having reworked the former structure of the upper mantle and enriched it in aqueous fluids. The effect of this active asthenosphere on the lithosphere gave rise to intense Late Cenozoic deformation, magmatism, and eventually resulted in mountain building.