Modelling the influence of pre-collisional rift linkage during mountain building

It is well documented that many mountain belts, like the Pyrenees, European Alps, Greater Caucasus, or Atlas, form to a large degree by the inversion of pre-collisional extensional basins. Looking at present-day extensional systems, we observe that one of their first order characteristics is rift segmentation with offset sub-basins that are linked through transfer zones. However, the impact of rift segmentation and linkage structures on subsequent mountain building remains unknown. Here, we use the 3D thermo-mechanical geodynamic model pTatin3D that is coupled to the fluvial landscape evolution model FastScape to investigate the effects of offset rift basins on subsequent basin inversion and mountain building. Presenting numerical models and a work minimization analysis, we show that rift linkage during extension depends on rift basin offset. The inversion of offset rift basins during mountain building can be subdivided into a juvenile and a mature stage. During the juvenile stage, extensional structures are reactivated, forming a mountain belt that resembles the basin structure. Further growth during the mature stage is determined by the emerging subduction polarity, which depends on pre-collisional basin offset and the nature of pre-existing weaknesses. Small offsets or pre-existing weaknesses that dip in the same direction lead to same-polarity subduction, which preserves the extensional template in the mountain belt. Basin offsets larger than ~30 km favour opposite polarity subduction, which eradicates the pre-collisional basin structure. Based on first-order model characteristics, we propose a simple template, in which mountain belt topography and dominant valley orientations can be used to infer deformation at depth. Comparison with the Greater Caucasus, Atlas, and Pyrenees shows that the Greater Caucasus is a type-example of a mature same-polarity subduction orogen, the Atlas is a juvenile inversion orogen where subduction polarity does not play a significant role, and the Pyrenees are a mature same-polarity orogen, which exhibits several additional complexities.