Sediment control on subduction plate speeds
Sediment control on subduction plate speeds
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DOI：
10.1016/j.epsl.2018.08.057
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发表时间：
2018-11
影响因子：
5.3
通讯作者：
W. Behr;T. Becker
中科院分区：
文献类型：
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作者：
W. Behr;T. Becker
构造板块速度主要是俯冲板块势能变化与地幔黏性耗散、弯曲岩石圈和板块-上板块界面平衡的结果。一系列观察表明，板块可能很弱，这意味着板块界面耗散的作用比以前认为的更为突出。由于流体丰富和接近静岩孔隙流体压力，通常认为浅层逆冲界面较弱，但很少关注深层粘性界面的影响。研究表明，俯冲带深部界面粘度受俯冲至深部的沉积岩与基性岩相对比例的强烈影响。下行板块沉积物稀疏，深部界面以变质为榴辉岩的基性岩性为主，其黏度比软流圈地幔高1 ~ 2个数量级，降低了俯冲板块速度。相比之下，在沉积物丰富且向深部俯冲的地方，深层界面粘度比软流圈地幔低1-2个数量级，从而使板块速度明显更快。俯冲板块速度与深部沉积物俯冲之间的这种相关性可能有助于解释收敛速度的急剧加速（或减速），例如中新生代印度-亚洲收敛的加速记录。
Tectonic plate velocities predominantly result from a balance between the potential energy change of the subducting slab and viscous dissipation in the mantle, bending lithosphere, and slab–upper plate interface. A range of observations suggest that slabs may be weak, implying a more prominent role for plate interface dissipation than previously thought. The shallow thrust interface is commonly assumed to be weak due to an abundance of fluids and near-lithostatic pore fluid pressures, but little attention has been paid to the influence of the deeper, viscous interface. Here we show that the deep interface viscosity in subduction zones is strongly affected by the relative proportions of sedimentary to mafic rocks that are subducted to depth. Where sediments on the down-going plate are sparse, the deep interface is dominated by mafic lithologies that metamorphose to eclogites, which exhibit viscosities 1–2 orders of magnitude higher than the asthenospheric mantle, and reduce subduction plate speeds. In contrast, where sediments are abundant and subducted to depth, the deep interface viscosity is 1–2 orders of magnitude lower than the asthenospheric mantle, thus allowing significantly faster plate velocities. This correlation between subduction plate speed and deep sediment subduction may help explain dramatic accelerations (or decelerations) in convergence rates, such as the acceleration documented for India–Asia convergence during the mid-Cenozoic.