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Zusammenfassung:
Stable continental cratons are the oldest geologic features on the planet. They have survived 3.8 to 2.5 billion years of Earth’s evolution1, 2. The key to the preservation of cratons lies in their strong and thick lithospheric roots, which are neutrally or positively buoyant with respect to surrounding mantle3, 4. Most of these Archaean-aged cratonic roots are thought to have remained stable since their formation and to be too viscous to be affected by mantle convection2, 3, 5. Here we use a combination of gravity, topography, crustal structure and seismic tomography data to show that the deepest part of the craton root beneath the North American Superior Province has shifted about 850 km to the west–southwest relative to the centre of the craton. We use numerical model simulations to show that this shift could have been caused by basal drag induced by mantle flow, implying that mantle flow can alter craton structure. Our observations contradict the conventional view of cratons as static, non-evolving geologic features. We conclude that there could be significant interaction between deep continental roots and the convecting mantle.
