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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 >Dynamic uplift in a transpressional regime: numerical model of the subduction area of Fiordland, New Zealand
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Dynamic uplift in a transpressional regime: numerical model of the subduction area of Fiordland, New Zealand

机译：超压状态下的动态隆升：新西兰峡湾地区俯冲区的数值模型

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摘要

Bending of the downgoing plate in subduction zone typically leads to an offshore peripheral bulge. This leads to dynamic uplift generated by the elastic bending of the subducted slab, and is generally enough to support the topography of the bulge in a non-isostatic manner and produce a positive gravity anomaly. The Southwest region of the South Island of New Zealand, Fiordland, is characterized by high elevation and a large positive Bouguer gravity anomaly. This combination of high topography with high Bouguer gravity argues against isostatic equilibrium and suggests an additional support mechanism. Earthquakes as deep as 150 km, a deformed Benioff zone and inferences from plate reconstructions all support a tectonic model where the eastern margin of the Australian plate is subducting beneath Fiordland and is sharply bent. This bending of the Australian plate provides the needed non-isostatic support for Fiordland topography and generates the observed gravity anomaly. Although the peripheral bulge in subduction zones is generally localized offshore, the positive gravity anomaly (Bouguer and free air) in Fiordland is onshore, close to the shoreline, and generally corresponds spatially with high elevations. Here we propose a mechanism that allows the subducted sliver of slab to be decoupled from the main Australian plate and strongly bent beneath Fiordland. We test this scenario with a finite-element model. The model allows us to study the flexural response of a subducting elastic slab bent by lateral compression into a shape similar to the one inferred from seismicity. We test how different plate geometries and plate boundary forces influence the flexural dynamic support of Fiordland topography, providing important constraints on the local plate dynamics. The model results show that for a tectonically reasonable combination of plate geometries and boundary forces, the deformation of the lithosphere produces the observed topography and gravity signature. In particular we find that the bending of the subducted Australian plate can supply the needed uplift and support for the topography of Fiordland. However, a weak area west of but nearby the Fiordland shoreline, perhaps a fault or tear, is needed to decouple the subducted sliver, confine the bulge, and localize the uplift within Fiordland.
机译：俯冲带中下降板的弯曲通常会导致海上外围凸起。这导致了俯冲板的弹性弯曲产生的动态抬升，并且通常足以以非等静方式支撑凸起的形貌并产生正重力异常。新西兰南岛的西南地区，峡湾地区，具有高海拔和大的正布格重力异常的特征。高地形与高布格引力的这种结合反对等静压平衡，并提出了附加的支撑机制。长达150公里的地震，贝尼奥夫（Benioff）变形带以及板块重建的推论都支持一种构造模型，其中澳大利亚板块的东缘俯冲到峡湾以下，并急剧弯曲。澳大利亚板块的这种弯曲为Fiordland地形提供了所需的非等静压支撑，并产生了观测到的重力异常。尽管俯冲带中的外围凸起通常位于海上，但峡湾地区的正重力异常（布格和自由空气）在陆地上，靠近海岸线，并且在空间上通常与高海拔相对应。在这里，我们提出了一种机制，可以使俯冲的板条与澳大利亚主板解耦，并在Fiordland下方强烈弯曲。我们使用有限元模型测试此方案。该模型使我们能够研究俯冲的弹性板的弯曲响应，该板通过横向压缩而弯曲成与地震活动相似的形状。我们测试了不同的板块几何形状和板块边界力如何影响Fiordland地形的弯曲动力支持，从而对局部板块动力学提供了重要的约束。模型结果表明，对于板块几何形状和边界力的构造合理组合，岩石圈的变形产生了观测到的地形和重力特征。特别是，我们发现俯冲的澳大利亚板块的弯曲可以为峡湾地区的地形提供所需的隆起和支撑。但是，需要在Fiordland海岸线以西但附近的薄弱区域（可能是断层或裂缝）来将俯冲的条带解耦，限制凸起并在Fiordland内定位隆升。

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