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

中文翻译：

---

造山楔建造过程中的浮力与剪切力

碰撞造山带的生长动力学主要受浮力和剪切力控制。然而，这些力量的相对重要性、它们的时间演变以及它们对造山楔构造样式的影响仍然难以捉摸。在这里，我们量化了碰撞造山过程中的浮力和剪切力，并研究了它们对造山楔形成和地壳岩石折返的影响。我们利用二维岩石学-热力学数值模拟长期（约 170  Myr) 岩石圈变形循环包括随后的超伸展、冷却、收敛、俯冲和碰撞。过度伸展产生了一个盆地，其中的大陆地幔被不对称的被动边缘包围。在收敛之前，我们用蛇纹岩代替了被挖掘的地幔顶部的几公里，以研究其在俯冲和碰撞过程中的作用。我们研究了三个参数的影响：（1）蛇纹岩的剪切阻力或强度，控制演化的强度俯冲界面；(2)大陆上地壳强度；(3) 俯冲物质的密度结构。密度由线性化状态方程或岩石相平衡计算确定。这三个参数控制向上浮力与水平驱动力之比的演变，$F_{\mathrm{乙}}/F_{\mathrm{D}}={\mathrm{氩气}}_{\mathrm{F}}$，它控制着造山带楔形的形成模式：Ar _F ≈0.5导致逆冲片主导的楔形，Ar _F ≈0.75由于上板块下方俯冲地壳的重新分层而导致较小的楔形形成，Ar _F ≈1导致浮力流- 或底辟主导的楔形，涉及从很深的地方（>80 公里）挖掘地壳物质。此外，采用相平衡密度模型的比利牛斯形成期间减少了由几个kilometres.We楔的平均地形表明，氩_˚F ⪅ 0.5由于缺乏高档变质岩，而对于阿尔卑斯山脉的Ar _˚F ≈1高档岩石和折返过程中的Ar _˚F ⪅ 0.5在碰撞后的阶段。在模型中，F _D在楔形生长和俯冲过程中增加，最终达到启动俯冲所需的量级 ( ≈18  TN m ^-1 )。继续推动俯冲所需的水平力的这种增加可能“扼杀”了欧洲板块在 35 到 25 Ma之间的亚得里亚海板块的俯冲， 并可能导致板块运动的重组和亚得里亚海板块的俯冲开始.