Architecture of Subducted Rifted Continental Margin and Dynamics of Early Collision

The transition from subduction to collision marks a pivotal geological transformation as tectonic plates cease their subduction, giving rise to intense collisions that reshape landscapes and foster the creation of mountain ranges. We use thermo-mechanical numerical modeling to address the dynamics of continental margin subduction and the subsequent transition to collision.

Several collision orogens like the Alps document a typical series of events that are not fully understood:

1. Continental high-pressure (HP) units are formed from upper crust and only during early continental subduction. In a mature collision orogen continental upper crust is detached from lower crust at shallow levels, while lower crust might continue to subduct.

2. These units are rapidly exhumed along the subduction boundary and their final position in the orogen is “in-sequence” on top of the continental nappes and below the oceanic suture. Continental HP-units are sandwiched between units that experienced considerably lower peak pressures.

3. Rapid exhumation of HP units is followed by:

3.1 apparently extensional deformation, of which at least the final stage affects the entire nappe pile;

3.2 a phase of magmatic activity, i.e. the formation of granodioritic and tonalitic intrusions that cut the established nappe pile;

3.2 rapid rise of topography in the orogen.

In order to investigate this sequence of events and recognize factors controlling their timings and necessary conditions we reconstruct transition from subduction to collision with forward modeling. Here, we employ visco-elasto-plastic thermomechanical modeling approach to model subduction process followed by collision.