Subducting slabs provide the main driving force for plate motion and flow in the Earth's mantle, and geodynamic, seismic and geo-chemical studies offer insight into slab dynamics and subduction-induced flow. Most previous geodynamic studies treat subduction zones as either infinite in trench-parallel extent (that is, two-dimensional) or finite in width but fixed in space. Subduction zones and their associated slabs are, however, limited in lateral extent (250-7,400 km) and their three-dimensional geometry evolves over time. Here we show that slab width controls two first-order features of plate tectonics—the curvature of subduction zones and their tendency to retreat backwards with time. Using three-dimensional numerical simulations of free subduction, we show that trench migration rate is inversely related to slab width and depends on proximity to a lateral slab edge. These results are consistent with retreat velocities observed globally, with maximum velocities (6-16 cm yr~(-1)) only observed close to slab edges (< l,200 km), whereas far from edges (> 2,000 km) retreat velocities are always slow (< 2.0 cm yr~(-1)). Models with narrow slabs (≤ 1,500 km) retreat fast and develop a curved geometry, concave towards the mantle wedge side. Models with slabs intermediate in width (～2,000-3,000 km) are sublinear and retreat more slowly. Models with wide slabs (≥ 4,000 km) are nearly stationary in the centre and develop a convex geometry, whereas trench retreat increases towards concave-shaped edges. Additionally, we identify periods (5-10 Myr) of slow trench advance at the centre of wide slabs. Such wide-slab behaviour may explain mountain building in the central Andes, as being a consequence of its tectonic setting, far from slab edges.
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机译：俯冲板块是板块在地幔中运动和流动的主要驱动力，而地球动力学，地震和地球化学研究提供了对板块动力学和俯冲引起的流动的洞察力。以前的大多数地球动力学研究都将俯冲带视为在平行于沟渠的范围内是无限的（即二维的），或者在宽度上是有限的，但在空间上是固定的。但是，俯冲带及其相关的板块在横向范围（250-7,400 km）内受到限制，并且它们的三维几何形状会随时间而变化。在这里，我们表明板坯宽度控制着板块构造的两个一阶特征-俯冲带的曲率及其随时间向后退的趋势。使用自由俯冲的三维数值模拟，我们显示了沟槽迁移速率与板坯宽度成反比，并取决于与侧板边缘的接近程度。这些结果与整体观测到的退避速度一致，最大速度（6-16 cm yr〜（-1））仅在靠近板缘（<1200 km）时观察到，而远离边缘（> 2,000 km）则退避速度。总是很慢（<2.0 cm yr〜（-1））。狭窄平板（≤1,500 km）的模型会快速后退，并形成弯曲的几何形状，向着地幔楔侧凹陷。平板中间宽度（〜2,000-3,000 km）的模型是亚线性的，后退速度较慢。宽平板（≥4,000 km）的模型在中心几乎静止不动，并呈现出凸起的几何形状，而沟槽后退则朝着凹形边缘增加。此外，我们在宽板的中心确定了缓慢的沟槽前进周期（5-10 Myr）。这种宽板的行为可以解释安第斯山脉中部的山区建筑，这是其构造环境的结果，远离板边缘。
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