Buoyancy versus shear forces in building orogenic wedges

Abstract. The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance these forces, their temporal evolution impact on tectonic style orogenic wedges remain elusive. Here, we quantify forces during orogeny investigate wedge formation exhumation crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction collision. Hyperextension generates basin with exhumed continental mantle bounded asymmetric passive margins. Before replace top few kilometres serpentinite to its role study three parameters: (1) resistance, or strength, serpentinites, controlling strength evolving interface; (2) upper crust; (3) density structure subducted material. Densities determined linearized equations state petrological-phase equilibria calculations. parameters control ratio upward-directed force horizontal driving force, FB/FD=ArF, which controls mode formation: ArF?0.5 causes thrust-sheet-dominated wedges, ArF?0.75 minor due relamination crust below plate, ArF?1 buoyancy-flow- diapir-dominated material from great depth (>80 km). Furthermore, employing phase models reduces average topography several kilometres. suggest that Pyrenees ArF?0.5 absence high-grade metamorphic rocks, whereas for Alps rocks post-collisional stage. In models, FD increases growth eventually reaches magnitudes (?18 TN m?1) required initiate subduction. Such an increase in continue subduction, might have “choked” European plate Adriatic one between 35 25 Ma could caused reorganization motion initiation plate.