THE ROLE OF RIFT-INHERITED HYPEREXTENSION FOR THE FORMATION OF COLLISIONAL OROGENS: INSIGHTS FROM THE ALPS (WESTERN EUROPE)

Recent development in marine geophysics linked with ODP resulted in new discoveries that considerably changed the way we interpret rifted margins and as a consequence the way we may understand orogenic systems. Studies conducted in present-day rifted margins unravel the complex crustal architecture and spatial evolution of rift systems, formed by distinct domains including 1) equilibrated/weakly thin continental crust representing either continental ribbons, microcontinents or stable continents, 2) necking zones marking the transition from weakly to highly thin continental crust, 3) hyperthinned domains floored either by severely thinned continental crust or exhumed subcontinental mantle and 4) eventually oceanic crust.

However, the resulting pre-orogenic template still awaits to be integrated in models focusing on mountain belts formation. In this presentation, we explore how the complexity of rift-inheritance, and in particular hyperextension, may control the evolution and final architecture of the collisional stage of orogenic systems.

The Alpine belt in Western Europe constitutes one of best-studied orogenic system worldwide preserving the relics of the Alpine Tethys. Based on surface and geophysical data, we suggest that the architecture and evolution of Alpine orogeny are strongly controlled by rift inheritance. We propose that the architecture of the Alpine belt results from the orogenic collage of distinct domains of the former rifted margins. The intensity of the reactivation and inversion of these former domains within the orogen is a direct consequence of their pre-orogenic architecture and crustal thickness. The highly deformed internal part samples the remnants of hyperthinned domains whereas the weakly deformed external parts preserve domains that where only weakly affected by the rifting. Consequently, the evolution of the Alpine orogen strongly depends on the architecture of the former rifted margins. The transition from subduction to collisional stage occurs when the necking zones and thick continental crust become involved in subduction, acting as buttresses.

Eventually, the adoption of a more “realistic” pre-orogenic template may lead to a better understanding of mountain belt formation processes but may also provide new insights for plate tectonic reconstructions.