Stalled slab dynamics
Stalled slab dynamics
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失速板坯动力学
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
M. Gurnis
中科院分区：
文献类型：
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作者：
E. Burkett;M. Gurnis
最近对北美西部地幔的地震成像揭示了从羽流到岩石圈水滴和板片碎片的复杂结构。爱达荷州下方的一个突出的高速“幕”被解释为自>；40 Ma以来在上地幔内悬挂的俯冲法拉隆板块的残余。因此，利用数值模型，我们探索了板块碎片可能在地幔中持续数千万年的流变学、化学、几何和动力学条件。仅有热浮力，延伸到500公里深的失速板块在∼17英里年内往往会分离并垂直下沉。对于这里探索的板坯年龄和流变性条件，以及较短的板坯40英里。上、下地幔粘性差的增大(1.4×到100×)可以减缓下沉速度，延长板块悬挂时间达5英里。动态效应，如附近活跃的俯冲引起的效应，只略微推迟或不影响失速的板块分离时间，但确实影响板块的几何形状，因为它们对楔子内的吸力压力做出反应。总体而言，浮力、粘性、几何和动力因素的组合可能会导致板材延长失速，而我们在这里探索的实际范围内的条件到目前为止可以解释长达28英里的延迟。
Recent seismic imaging of the mantle beneath western North America reveals complexities interpreted as structures ranging from plumes to lithospheric drips and slab fragments. A prominent high-velocity "curtain" beneath Idaho has been interpreted as a remnant of the subducted Farallon plate left dangling within the upper mantle since >40 Ma. Consequently, using numerical models, we explore the rheological, chemical, geometrical, and dynamic conditions under which a slab fragment might persist in the mantle for tens of millions of years. With thermal buoyancy alone, stalled slabs extending to 500 km depth tend to detach and sink vertically within ∼17 m.y. for the slab age and rheologic conditions explored here, and shorter slabs 40 m.y. An increase in upper- to lower-mantle viscosity contrast (1.4× to 100×) can slow sinking velocities and extend slab dangling time by up to 5 m.y. Dynamic effects such as those arising from active nearby subduction only slightly delay or do not affect stalled slab detachment timing but do affect the geometry of the slabs as they respond to suction pressures within the wedge. Overall, a combination of buoyant, viscous, geometric, and dynamic factors may allow cases of extended slab stalling, and conditions we explore here within realistic ranges can so far account for a delay of up to 28 m.y.