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The East Carpathians; indications for phase transitions, lithospheric failure and decoupled evolution of thrust belt and its forelandстатья
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Дата последнего поиска статьи во внешних источниках: 10 августа 2018 г.
- Авторы: Artyushkov E.V., Baer M.A., N-A Mörner
- Журнал: Tectonophysics
- Том: 262
- Год издания: 1996
- Издательство: Elsevier BV
- Местоположение издательства: Netherlands
- Первая страница: 101
- Последняя страница: 132
- DOI: 10.1016/0040-1951(95)00207-3
- Аннотация: An analysis is presented of the tectonic development of the East Carpathians since the Late Oligocene. The geological and geomorphological data show that five epochs of convergence and nappe emplacement took place with the last one occurring 11–12 m.y. B.P. After these compressional events the nappe surface remained near sea level. The crustal uplift which formed the present mountains began 3 m.y. B.P. and after 99% of the shortening of the Carpathians had been completed. The Pre-Carpathian foreland basin, up to 3–5 km deep, formed on the margin of the East European Platform in the Middle Miocene. Analysis of the evolution of the basin shows that it deepened away from the nappe-stack and most of the subsidence occurred when there was no convergence. This precludes lithospheric flexure due to convergence as a mechanism for basin formation. At 11–12 m.y. B.P. the inner part of the basin, ∼ 50 km wide, was overridden by the Carpathian nappe, up to 12–14 km thick. At that time, a slight crustal uplift took place, rather than subsidence, in the shallow remnant-outer basin part (the present foredeep) which emerged above sea level. An additional 7–8 km of subsidence then occurred in the foredeep of the southeastern Carpathians in the Late Miocene-Early Pleistocene when very little convergence took place. The evolution of the Carpathian foredeep shows that lithospheric flexure of 2–5 km occurred in regions, 20–40 km wide. Similar amounts of flexure and large basement faults exist under the nappe. This style of deformation indicates flexural rigidity of the lithosphere that is several orders of magnitude smaller than in stable cratonic regions. Under a low flexural rigidity, the crust should be close to local isostasy. Then the isostatic response to superposition of a 10–13-km-thick nappe on the platform margin which was near sea level would form high mountains. The crustal surface, however, remained at a low altitude. We interpret this to be the result of contraction of gabbro in the lower crust with the formation of dense garnet granulites during nappe emplacement. A layer of these dense rocks, ∼ 20 km thick, with P-wave velocities 7.5–7.6 km/s, exists in the lower crust of the East Carpathians. According to the geophysical data, there is no cool high-velocity slab now subducting towards the Intra-Carpathian area. An increase in the mean height of the Carpathians by only ∼ 1 km since the termination of convergence precludes a recent slab detachment. Rapid metamorphism of mafic rocks in the lower crust requires the infiltration of volatiles from the asthenosphere. Infiltration of volatiles into mantle lithosphere and the upper crust could strongly reduce their viscosity. These phenomena might be the cause of an abrupt loss of lithospheric rigidity on the margin of the East European Platform in the Neogene. Lithospheric failure allowed the incorporation of this region into the Carpathian fold belt after a long period of cratonic development.
- Добавил в систему: Артюшков Евгений Викторович