The influence of rifting on escarpment migration on high elevation passive continental margins
The influence of rifting on escarpment migration on high elevation passive continental margins
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裂谷对高海拔被动大陆边缘陡坡迁移的影响
DOI：
10.1029/2011jb008547
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发表时间：
2012
影响因子：
--
通讯作者：
P. Beek
中科院分区：
文献类型：
--
作者：
V. Sacek;J. Braun;P. Beek
通过结合地表过程、弯曲均衡、断裂和裂谷热效应的数值模型，我们表明，如果裂谷侧翼下的下地壳被大幅拉伸，在裂谷侧翼由机械卸载和弯曲反弹形成的断界悬崖作为退缩悬崖“存活”的可能性很小。在这种构造中，一个持续存在的分水岭出现在最初的陡坡向陆地的位置，靠近裂谷事件期间产生的次级隆起，其距离取决于上地壳的弯曲刚度。此外，当裂谷前地形向陆倾时，断裂带向次级隆起的迁移发生，否则断裂带的演化受原有内陆水系分划的引导。为了说明这种被动边缘演化的新机制，我们以澳大利亚东南部和巴西东南部为例进行了研究。我们认为，一个与裂谷相关的侧隆升的预先存在的内陆水系分水岭可以产生在澳大利亚东南部观测到的双重水系分水岭。另一方面，我们得出结论，巴西东南部边缘的Serra do Mar悬崖可能起源于持续时间的裂谷作用期间的二次弯曲隆起。在这两种情况下，撤退的陡坡不太可能发生，目前的边缘形态可以解释为仅由与裂谷相关的垂直运动造成的，而不需要显著的裂谷后“恢复”。
[1] Using numerical models that couple surface processes, flexural isostasy, faulting and the thermal effects of rifting, we show that fault-bounded escarpments created at rift flanks by mechanical unloading and flexural rebound have little potential to “survive” as retreating escarpments if the lower crust under the rift flank is substantially stretched. In this configuration, a drainage divide that persists through time appears landward of the initial escarpment in a position close to a secondary bulge that is created during the rifting event at a distance that depends on the flexural rigidity of the upper crust. Moreover, the migration of the escarpment to the secondary bulge occurs when the pre-rift topography dips landward, otherwise the evolution of the escarpment is guided by the pre-existing inland drainage divide. To illustrate this new mechanism for the evolution of passive margins, we study the examples of Southeastern Australia and Southeastern Brazil. We propose that a pre-existing inland drainage divide with rift related flank uplift can produce the double drainage divide observed in Southeastern Australia. On the other hand, we conclude that it is possible that the Serra do Mar escarpments on the Southeastern Brazilian margin originated as a secondary flexural bulge during rifting that persisted through time. In both cases, the retreating escarpment scenario is unlikely and the present-day margin morphology can be explained as resulting from rift-related vertical motions alone, without requiring significant post-rift “rejuvenation”.