Distensional Mediterranean and World Orogens

Abstract

An overview of the modern progresses of the expanding Earth conceptions as they come out from new data and their possible interpretations is provided in this paper. The starting point of this review is the new detailed 3D distributions of relocated hypocenters laying under orogenic belts. The similarity of the hypocentral patterns under the Tethyan orogenic belts, and under the South American Pacific orogenic margin is considered to be a major font of information on which to build a more realistic global geodynamic model. Clusters and filaments of hypocenters are recognizable instead of regular patterns. These clusters taper downwards, leading to the idea of a deep origin in narrow regions of disturbance, besides other important facts that witness in favour of surfaceward movements of deep material along what can be called "mega-dykes". The outpouring of the material on the surface produces gravitational nappes and their overthrust on the sediments of the preexisting trough, forcing them on a burial path which emulate the subduction process, but without reaching depths greater than 50-70 km. Phenomenons like metamorphism, mixing, migmization, upward transport of fragments of the buried lithosphere etc. are possible at the boundary between uplifting material and down-pushed crust and lithosphere. Additional clues can be collected that confirm the new proposed framework. The astronomical indications of a coseismic displacement of the instantaneous Earth’s rotation axis in the occasion of the great Sumatra (Mw=9.3) and Honshu (Mw=9.0) earthquakes are especially significant because in complete disagreement with the plate tectonics modelled axis shift and in agreement with the shift expected in the new conception. Because of analogous opposite predictions of the length of day variation following the extreme magnitude earthquakes (ΔLOD<0 vs ΔLOD>0), future improvements of the time measurement techniques could allow a final choice between rival geodynamical models.