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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Softening trigerred by eclogitization, the first step toward exhumation during continental subduction
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Softening trigerred by eclogitization, the first step toward exhumation during continental subduction

机译：大陆化俯冲过程中的尸体化第一步

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Direct observation of peak pressure deformation in exhumed subduction channels is difficult because little evidence of this deformation survives later syn-exhumation deformation. Most ultrahigh-pressure parageneses are found in continental derived metamorphic rocks making continental subduction the best context to observe peak pressure deformation. Whereas many studies have enlightened the main driving parameters of exhumation such as buoyancy forces, low viscosity in the subduction channel, overburden removal by erosion and normal faulting, a basic question is seldom considered: why is a tectonic unit disconnected from the descending lithosphere and why does it start its way towards the surface? This event, seminal to exhumation processes, must involve some deformation and decoupling of the exhumed slice from the descending slab at peak pressure conditions or close to it. Our field observations in the Bergen arc show that Caledonian eclogitization and later amphibolitization of a granulitic terrane was achieved with a consistent component of simple shear compatible with the sense of the Caledonian subduction. Thus, the sequence of deformation preserved in the Bergen Arc documents the decoupling of subducted crustal material from the descending slab at the onset of exhumation. This observation suggests that deformation in the subduction channel is largely controlled by kinematic boundary conditions, i.e. underthrusting of the subducting slab. In this context of simple shear, metamorphic reactions assisted by firacturating, fluid infiltration and ductile deformation lower the resistance of rocks and allow the localisation of shear zones and the decoupling of buoyant tectonic units from the subducting slab. These tectonic units can then be incorporated into the channel circulation and start their upward travel. (c) 2005 Elsevier B.V. All rights reserved.
机译：很难直接观察挖掘出的俯冲通道中的峰值压力变形，因为这种变形的证据很少能在后来的同发掘变形中幸存。在大陆衍生的变质岩中发现了大多数超高压共生物，使大陆俯冲成为观察峰值压力变形的最佳环境。尽管许多研究启发了挖掘尸体的主要驱动参数，例如浮力，俯冲通道中的低粘度，通过侵蚀和正断层的覆盖层清除，但很少考虑一个基本问题：为什么构造单元与下降的岩石圈断开连接？为什么它是否开始向表面移动？此事件是开挖到发掘的重要过程，必须在峰值压力条件或接近峰值压力的条件下，使发掘出的薄片与下降的平板发生变形和解耦。我们在卑尔根弧线的实地观测表明，用简单剪切的一致成分与喀里多尼亚俯冲的感觉一致，就实现了花岗岩地层的喀里多尼亚旋化和后来的两性化。因此，保留在卑尔根弧线中的变形序列记录了在发掘尸体开始时俯冲的地壳材料与下降的平板之间的解耦。该观察结果表明俯冲通道中的变形在很大程度上受运动学边界条件的控制，即俯冲板块的下冲作用。在简单剪切的背景下，通过煅烧，流体渗透和延性变形辅助的变质反应降低了岩石的阻力，并允许剪切带的局部化和浮生构造单元与俯冲板的解耦。然后可以将这些构造单元合并到河道循环中并开始向上移动。 （c）2005 Elsevier B.V.保留所有权利。

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