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首页> 外文期刊>Journal of geodynamics >A simple toy model for coupled retreat and detachment of subducting slabs
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A simple toy model for coupled retreat and detachment of subducting slabs

机译：俯冲板块退缩与脱开的简单玩具模型

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Subducting slabs are the primary drivers of plate tectonics and mantle circulation, but can also undergo various instabilities that cause dramatic adjustments in tectonic evolution and motion. Slab rollback or trench retreat is possibly a dominant form of time dependence in the plate-mantle system, causing plates to shrink and the mantle to undergo complex flow patterns. Likewise, slab detachment can induce abrupt adjustments in both plate motions and vertical displacement of continents. The arrival or accumulation of continental crust over a subduction zone induces high stresses on the plate and slab that can trigger either rollback or detachment or both. However, these processes necessarily interact because of how stress is relieved and plate motions altered. Here we present a simple boundary-layer like model of coupled trench retreat and slab detachment, induced by continent accumulation, and with slab necking augmented by grain-damage self-weakening (to allow for abrupt necking). With this model we find that, with continental accumulation, initial rollback is at first modest. However, as the stress from continental accumulation peaks, it triggers abrupt slab detachment. The subsequent slab loss causes the plate to lose its primary motive force and to thus undergo a more dramatic and rapid rollback event. After the larger rollback episode, the contracted continental mass re-expands partially. Plausible grain damage parameters and 40km thick crust cause abrupt detachment and major rollback to occur after a few hundred million years, which means the plates remain stable for that long, in agreement with the typical age for most large plates. While the complexity of some field areas with a well documented history of detachment and rollback, such as the Mediterranean, taxes the sophistication of our toy model, other simpler geological examples, such as on the western North American plate, show that episodes of rollback can follow detachment.
机译：俯冲板块是板块构造和地幔环流的主要驱动力，但也可能经历各种不稳定性，从而导致构造演化和运动发生重大变化。在板-幔系统中，平板回滚或沟槽退缩可能是时间依赖性的主要形式，这导致板收缩并使幔经历复杂的流动模式。同样，板块的分离会引起板块运动和大陆的垂直位移的突然调整。大陆壳到达俯冲带或在俯冲带上聚集会在板块和平板上产生高应力，从而可能引起回滚或分离或两者兼有。然而，由于如何减轻应力和改变板的运动，这些过程必然相互作用。在这里，我们提出了一个简单的边界层模型，该模型由大陆堆积引起，并伴有沟槽退缩和板坯分离的模型，并且板坯颈缩通过晶粒破坏自弱化（允许突然颈缩）来增强。通过该模型，我们发现，随着大陆的积累，初始回滚起初是适度的。但是，随着大陆堆积的应力达到峰值，它会触发突然的平板脱离。随后的板坯损失导致板丧失其主要动力，因此经历了更加剧烈和迅速的回滚事件。在发生较大的回滚事件之后，收缩的大陆质量部分扩大。合理的晶粒损伤参数和40 km厚的地壳会导致突变，并在几亿年后发生大的回滚，这意味着这些板块可以保持这么长时间的稳定，这与大多数大型板块的典型寿命相符。尽管某些具有分离和回滚历史记录的野外区域的复杂性（例如地中海）使我们的玩具模型变得更加复杂，但其他更简单的地质示例（例如北美西部板块）显示，回滚事件可以跟随支队。

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