Simulation of late Cenozoic South American flat-slab subduction using geodynamic models with data assimilation
Simulation of late Cenozoic South American flat-slab subduction using geodynamic models with data assimilation
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DOI：
10.1016/j.epsl.2016.01.011
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发表时间：
2016-03-15
影响因子：
5.3
通讯作者：
Zhou, Quan
中科院分区：
文献类型：
--
作者：
Hu, Jiashun;Liu, Lijun;Zhou, Quan
南美地区平板的形成机制尚不清楚。为了定量评估先前提出的机制，我们使用四维地球动力学模型模拟了南美洲以下100 Ma后的俯冲历史，根据最近的地质重建，逐步纳入了板块运动学、海底年龄和关键构造特征，包括浮力洋壳、大陆克拉通、大洋高原(即推断的印加高原、俯冲的纳斯卡海脊和胡安·费尔南德斯海脊)以及可变形海沟剖面。我们发现，在没有俯冲板块和俯冲浮力特征的情况下，海底年龄通过控制板块的机械强度(即抗弯能力)和负浮力(增强弯曲的综合正密度异常)来影响板块倾角。我们的模型表明，在年龄&30 Ma时，板材的浮力占主导地位，而在更年轻的年龄，则相反。厚覆盖板的存在通过增加动态吸力减少了板岩倾角，个别克拉通根部进一步导致倾角减小的沿海沟的变化。虽然来自上覆板块的动态吸力导致长波板片倾角的永久性减小，但正如观察到的那样，是俯冲大洋高原和无震海脊的最终添加产生了瞬变和局部化的板片。这些结果表明，除浮力特征外，所有机制仅在大空间尺度上影响板坯倾角。我们的最佳模型包含了上述所有构造特征，为上地幔贝尼奥夫带和中中新世以来火山弧的时间演化提供了很好的匹配。秘鲁板块的不完美匹配很可能与亚马逊克拉通不确定的3D形态有关。爱思唯尔出版公司(Elsevier B.V.)
The formation mechanisms of flat slabs in South America remain unclear. To quantitatively evaluate the earlier proposed mechanisms, we simulate the post-100 Ma subduction history below South America using 4-D geodynamic models by progressively incorporating plate kinematics, seafloor ages and key tectonic features including the buoyant oceanic crust, continental cratons, oceanic plateaus (i.e. the inferred Inca plateau, subducting Nazca Ridge and Juan Fernandez Ridge), as well as deformable trench profiles according to recent geological reconstructions. We find that, in the absence of an overriding plate and subducting buoyancy features, the seafloor age affects slab dip angle by controlling the slab's mechanical strength (i.e., the resistance to bending) and negative buoyancy (integrated positive density anomaly that enhances bending). Our models show that slab strength dominates its buoyancy at age >30 Ma and the opposite for younger ages. The existence of a thick overriding plate reduces the slab dip by increasing dynamic suction, and individual cratonic roots further lead to along-trench variations of dip angle reduction. While dynamic suction from the overriding plate generates a permanent reduction of the long-wavelength slab dip angle, it is the final addition of subducting oceanic plateau and aseismic ridges that produces the transient and localized flat-slabs as observed. These results suggest that all mechanisms except the buoyancy features affect the slab dip only at large spatial scales. Our best-fit model with all the above tectonic features included provides a good match to both the upper mantle Benioff zones and the temporal evolution of volcanic arcs since the mid-Miocene. The imperfect match of the Peruvian flat-slab is likely associated with the uncertain 3-D configuration of the Amazonian craton. Published by Elsevier B.V.