Erosional dynamics, flexural isostasy, and long-lived escarpments: A numerical modeling study
Erosional dynamics, flexural isostasy, and long-lived escarpments: A numerical modeling study
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DOI：
10.1029/94jb00320
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发表时间：
1994-06
影响因子：
--
通讯作者：
G. Tucker;Rudy Slingerland
中科院分区：
文献类型：
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作者：
G. Tucker;Rudy Slingerland
侵蚀悬崖是高海拔裂谷大陆的共同特征。裂变径迹数据表明，这些悬崖是由裂谷过程中基准面降低和/或边缘抬升形成的，随后侵蚀锋面横向后退数十至数百公里。先前的模拟研究表明，这种特征性的剥蚀模式会对边缘均衡隆起和近海沉积盆地的演化产生深远的影响。然而，目前对能够驱动如此长时间的悬崖后退的地貌机制还只有初步的了解。在这项研究中，我们提出了一种非线性、二维景观演化模型，用于评估裂谷产生的悬崖长期后退的必要和充分条件。该模型将地形表示为单元网格，随着水以最陡下降的方向流经网格，排水网络不断演变。该模型解释了风化产生的沉积物、河流沉积物输送、基岩河道侵蚀以及扩散机制和质量破坏导致的山坡沉积物输送。提出的数值实验探讨了侵蚀过程的不同组合以及剥蚀和弯曲均衡隆起之间的动态耦合的影响。模型结果表明，断崖长期退缩的充要条件是：（1）随着流域面积的增加，侵蚀速率增大的基岩河道下切，使河道变陡并向源扩展； (2) 相对于沉积物输送效率而言，沉积物产生率较低，这促进了地形生成过程而不是扩散过程； (3)大陆海拔高，河流解剖有更大的自由度； (4) 任何有助于维持悬崖顶部附近排水分界的过程，包括弯曲等静压隆起。弯曲均衡隆起还通过抬高侵蚀悬崖附近的地形来促进悬崖后退，从而增加河道梯度并加速侵蚀，进而产生额外的均衡隆起。在所有上述条件中，高大陆海拔是大多数裂谷边缘悬崖所共有的，并且最终可能是最重要的因素。
Erosional escarpments are common features of high-elevation rifted continents. Fission track data suggest that these escarpments form by base level lowering and/or marginal uplift during rifting, followed by lateral retreat of an erosion front across tens to hundreds of kilometers. Previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins. Yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat. In this study we present a nonlinear, two-dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long-term retreat of a rift-generated escarpment. The model represents topography as a grid of cells, with drainage networks evolving as water flows across the grid in the direction of steepest descent. The model accounts for sediment production by weathering, fluvial sediment transport, bedrock channel erosion, and hillslope sediment transport by diffusive mechanisms and by mass failure. Numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift. Model results suggest that the necessary and sufficient conditions for long-term escarpment retreat are (1) incising bedrock channels in which the erosion rate increases with increasing drainage area, so that the channels steepen and propagate headward; (2) a low rate of sediment production relative to sediment transport efficiency, which promotes relief-generating processes over diffusive ones; (3) high continental elevation, which allows greater freedom for fluvial dissection; and (4) any process, including flexural isostatic uplift, that helps to maintain a drainage divide near an escarpment crest. Flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment, thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift. Of all the above conditions, high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor.