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Zusammenfassung:
Ocean closure and collisional orogeny frequently enrich the lithospheric mantle in radioactive elements (uranium, thorium, potassium) due to the subduction of continent-derived sediments and continental crust. According to thermal modeling, increased content of radioactive elements within the anomalous lithospheric mantle causes a time-dependent rise of temperature, providing favorable conditions for intracontinental rifting more than 50-100 million years after the closure of the ocean. In addition, the obtained results indicate that in a global-scale mantle convection system, there is a clear tendency for the mantle upwellings to move towards the thermally anomalous upper-mantle block over time. Concentrating convectional upwellings under the anomalously hot lithosphere can cause extensional stresses that can theoretically trigger the break-up of the already thermally weakened, continental lithosphere. Moreover, our results provide an explanation of why rifting and continental break-up occur along or in close vicinity to the suture zones not immediately after the orogenic event but with a delay in time, dependent on the concentration of heat-producing elements in the anomalous mantle block and the size of this block. Thus, the presence of structural/compositional inhomogeneities within the anomalous lithosphere plays a rather secondary role, affecting mostly the geometrical configuration of the rifts. Therefore, a newly discovered, time-dependent process of weakening the continental lithosphere can be responsible for intracontinental rifting and the subsequent continental break-up and is controlled by the enhanced content of radioactive elements within the anomalous lithospheric mantle of the suture zones.
