Influence of Peruvian flat-subduction dynamics on the evolution of western Amazonia
Influence of Peruvian flat-subduction dynamics on the evolution of western Amazonia
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DOI：
10.1016/j.epsl.2014.07.027
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发表时间：
2014-05
影响因子：
5.3
通讯作者：
C. Eakin;C. Lithgow‐Bertelloni;F. Dávila
中科院分区：
文献类型：
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作者：
C. Eakin;C. Lithgow‐Bertelloni;F. Dávila
地幔中的对流主要是由冷密的俯冲板块驱动的，但关于板块形态和浮力的3D变化如何影响地幔流动或上面的表面如何变形的响应(即动态地形)，人们知之甚少。我们通过研究位于南美洲秘鲁的一个平板俯冲活动区的动力学来研究这一问题。在这里，根据区域地震活动，板片的几何形状是众所周知的，我们有来自当地地质记录的观测来验证我们的模型。特别令人感兴趣的是，Solimóes组在亚马孙西部普遍下沉和沉积，这与中新世中晚期秘鲁板块的发展相吻合。这一地层覆盖了从最深处到距离海沟2,000公里的普鲁斯拱门(∼)的大片区域。在靠近安第斯山脉的地方，可以很容易地用挠曲来解释几公里沉积厚度的保存。根据对安第斯山脉负荷的估计，我们预计跨度为100公里的住宿空间将达到2.8至3.6公里。然而，Solimóes建造的时空历史，特别是厚达1.2公里深的远端前陆堆积，只能与更长波长的动态地形源相匹配。在从正常俯冲过渡到平坦俯冲之后，我们预测将有超过1公里的动态下沉(∼1500公里宽)传播到距离海沟1000公里的地方，跟踪俯冲前沿。紧随其后的是在其后面的平坦部分上的动态抬升脉冲。因此，我们认为，秘鲁板片压平过程中的抬升、弯曲和动态地形共同作用，导致了亚马孙西部的沉积历史和地貌演变，最终导致了我们今天所知的亚马逊流域的构造。
Convection in the Earth's mantle is mainly driven by cold, dense subducting slabs, but relatively little is known about how 3D variations in slab morphology and buoyancy affect mantle flow or how the surface above deforms in response (ie dynamic topography). We investigate this problem by studying the dynamics of an active region of flat-slab subduction located in Peru in South America. Here the slab geometry is well known, based on the regional seismicity, and we have observations from the local geological record to validate our models. Of particular interest is the widespread subsidence and deposition of the Solimões Formation across western Amazonia that coincided with the development of the Peruvian flat-slab during the Mid-Late Miocene. This formation covers an extensive area from the foredeep to the Purus Arch located∼ 2000 km away from the trench. Close to the Andes the preservation of several kilometers of sedimentary thicknesses can be easily accounted for by flexure. Based on an estimate of the Andean loading we predict 2.8 to 3.6 km of accommodation space that spans 100 km. The spatial and temporal history of the Solimões Formation however, particularly the thick distal foreland accumulations up to 1.2 km deep, can only be matched with the addition of a longer-wavelength dynamic source of topography. Following the transition from normal to flat subduction, we predict over 1 km of dynamic subsidence (∼ 1500 km wide) that propagates over 1000 km away from the trench, tracking the subduction leading edge. This is followed by a pulse of dynamic uplift over the flat segment behind it. We therefore propose that a combination of uplift, flexure and dynamic topography during slab flattening in Peru is responsible for the sedimentation history and landscape evolution of western Amazonia that eventually led to the configuration of the Amazon Drainage Basin we know today.