Foredeep basins: the main features and model of formation

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• 作者：Mikhailov ; Valentine O. ; P. Timoshkina ; Elena ; Polino ; Riccardo
• 关键词：basin modelling ; foredeep formation ; small-scale convection ; the Great Caucasus
• 刊名：Tectonophysics
• 出版年：1999
• 出版时间：June 30, 1999
• 年：1999
• 卷：307
• 期：3-4
• 页码：345-359
• 全文大小：685 K

文摘

The comparative study of the foredeep basins of the northern Caucasus, Alpine and Apennine foredeeps revealed that there are no significant differences between outer and inner foredeeps situated at the front and the back of the crustal-scale thrust. So the driving mechanism should be essentially the same for internal and external foredeeps and elastic flexure should not be supposed as the only (sometimes as the main) mechanism of foredeep formation. The common feature of the foredeep evolution is a phase of slow subsidence lasting for 50 million years or more (passive margin stage sensu stricto) and then relative uplift followed by rapid subsidence. This twofold event of relative uplift (the duration is several million years) giving way to rapid subsidence may be repeated several times. The relative uplift or nearly equal to zero subsidence of the foredeep basins appeared to be synchronous with phases of external compression within adjacent mountain belts, as well as rapid subsidence took place between phases of external compression. Thus, the first stage of relative uplift could be recognised as the first stage of the foredeeps formation. To describe the development of the foredeeps at both sides of the compressional belts a model of evolution of the Earth's outer shell has been employed. The model predicts that when the Earth's outer shell has been once disturbed by external intraplate- or mantle-induced forces, small-scale convection within the asthenosphere arises. This convection causes deformation in the lithosphere of orogenic belts over a long period of time after the external forces stop. This manifests in uplift of belts and subsidence at their periphery. The suggested model shows a good agreement with data on the foredeeps structure and evolution. In particular, application of the model enabled us to explain the thickness of sediments in the foredeep basins and their shape, the formation of the foredeeps not only at the front but also at the back of asymmetric compressional thrust belts, uplift of foredeeps during compression in the belts and rapid subsidence after this compression stops. Numerical results for the Great Caucasus region showed that the first compressional event at the orogenic stage took place there before the formation of the Maykopian sediments, i.e. 39.5 Ma, in the end of the closure of the Arabian Ocean. The three further compressional events can also be recognised: one of them being between 16.6 and 15.8, the other between 14.3 and 12.3 Ma, and the last one between 7.0 and 5.2 Ma.