Evolution of the slab bending radius and the bending dissipation in three-dimensional subduction models with a variable slab to upper mantle viscosity ratio
Evolution of the slab bending radius and the bending dissipation in three-dimensional subduction models with a variable slab to upper mantle viscosity ratio
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DOI：
10.1016/j.epsl.2009.09.034
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发表时间：
2009-10
影响因子：
5.3
通讯作者：
W. Schellart
中科院分区：
文献类型：
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作者：
W. Schellart
提出了三维实验室俯冲模型，研究了板片/上地幔粘度比（ηSP/ηUM）对板片弯曲半径（RB）的影响，其中ηSP/ηUM=66-1375。在这里，RB 通过除以上地幔厚度 (TUM) 进行无量纲化。结果表明，RB/TUM随时间变化，在俯冲速度最大时达到最大值。此外，在研究的粘度范围内，RB/TUM 随着 ηSP/ηUM 的增加而近似线性增加。模型结果表明，与板坯负浮力 (FBu) 和下沉过程中释放的势能 (ФBu) 相比，板坯弯曲力 (FBe) 和弯曲过程中的能量耗散 (ФBe) 较小。 ФBe/ФBu(≈FBe/FBu)的最大值在俯冲早期达到，此时RB/TUMi最小且板片尖端位于220-440km深度。最大ФBe/ФBu随着ηSP/ηUM的增加而增加，当ηSP/ηUM=66、217、709和1375时，ФBe/ФBu(max)分别=0.06、0.11、0.18和0.22。对于俯冲深度 >220-440km，对于所有粘度比，ФBe/ФBu=0.02-0.11。假设自然界中的ηSP/ηUM<1000，并且板块平面曲率期间的粘性耗散≤1%，则模型预测自然界中板块的大部分势能用于驱动地幔流（平均88%-97%，最低81%），而只有一小部分用于在铰链处弯曲俯冲板块（平均2-11%，最高18%）。应用RB/TUM和ФBe/ФButo自然俯冲带的模型预测意味着，在自然界中，ηSP/ηUM=1-7×102和ηUM=0.8-2.7×1020Pa·s。最后，使用葡萄糖浆和硅油作为建模材料的实验室模型强调了实验过程中精确控制温度的重要性。新材料研究表明，这两种材料的粘度在3-33℃范围内随温度呈指数下降，密度随温度近似线性下降，热体积膨胀系数为3.8-4.2×10−4C−1（葡萄糖浆）和9.2×10−4C−1（硅油）。
Three-dimensional laboratory subduction models are presented investigating the influence of the slab/upper mantle viscosity ratio (ηSP/ηUM) on the slab bending radius (RB), with ηSP/ηUM=66-1375. Here, RBis non-dimensionalized by dividing it by the upper mantle thickness (TUM). The results show that RB/TUMvaries with time, reaching a maximum when the subduction velocity is maximum. Furthermore, RB/TUMincreases approximately linearly with increasing ηSP/ηUMfor the investigated viscosity range. The model results show that the slab bending force (FBe) and the energy dissipation during bending (ФBe) are small compared to the negative buoyancy force of the slab (FBu) and the potential energy release during sinking (ФBu). Maxima in ФBe/ФBu(≈FBe/FBu) are reached in the early stage of subduction when RB/TUMis minimum and the slab tip is at 220-440km depth. Maximum ФBe/ФBuincreases with increasing ηSP/ηUM, with ФBe/ФBu(max)=0.06, 0.11, 0.18 and 0.22 for ηSP/ηUM=66, 217, 709 and 1375, respectively. For subduction depths >220-440km, ФBe/ФBu=0.02-0.11 for all viscosity ratios. Assuming that in nature ηSP/ηUM<1000, and that viscous dissipation during plan view curvature of the slab is ≤1%, the models predict that in nature most of the slab's potential energy is used to drive mantle flow (on average 88%-97% and minimally 81%), whilst only a small component is used to bend the subducting plate at the hinge (on average 2-11% and maximally 18%). Applying the model predictions for RB/TUMand ФBe/ФButo natural subduction zones implies that in nature ηSP/ηUM=1-7×102and ηUM=0.8-2.7×1020Pa·s. Finally, the laboratory models, which use glucose syrup and silicone oil as modelling materials, highlight the importance of accurate control on temperature during an experiment. New material investigations show that the viscosity of these two materials decreases exponentially with temperature in the range 3-33 °C, their density decreases approximately linearly with temperature, and their coefficient of thermal volumetric expansion is 3.8-4.2×10−4C−1(glucose syrup) and 9.2×10−4C−1(silicone oil).