EAPS

Evgueni Burov
Professor of Geophysics
University Pierre et Marie Curie

The role of mantle-lithosphere interactions, lithosphere rheology and far-field stresses in shaping surface topography is a long debated topic. In general, it is supposed that mantle plumes and vertical mantle flows result in axisymmetric, long-wavelength topography, which strongly differs from generally asymmetric short-wavelength topography created by intraplate tectonic forces. However, identification of mantle-induced topography is difficult, especially in the continents. It can be argued therefore that complex brittle-ductile rheology and stratification of the continental lithosphere result in short-wavelength modulation and localization of deformation induced by mantle flow. This deformation should also be affected by far-field stresses and hence interplay with the “tectonic” topography (e.g., in ‘active/passive’ rifting scenario). Testing these ideas requires thermally and thermodynamically coupled 3D numerical mechanical modelling of mantle-lithosphere interactions, which so far has not been possible due to conceptual and technical limitations of earlier approaches. We present here new ultra-high resolution 3-D experiments on topography over mantle plumes, incorporating a weakly pre-stressed (ultra-slow spreading) rheologically realistic lithosphere. The model also accounts for partial melting and thermodynamic phase changes. The results show complex surface evolution, which is very different from smooth radially symmetric patterns usually assumed as the canonical surface signature of mantle upwellings. In particular, the topography exhibits strongly asymmetric small-scale 3D features, which include narrow and wide rifts, flexural flank uplifts and fault structures. In addition, synthetic seismic tomography patterns computed on the base of the model-predicted thermal and physical property distributions show complex signatures that are strongly dependent on the rheological assumptions. The experiments also predict complex mantle-lithosphere interactions near intra-plate boundaries associated with rheological discontinuities and lateral structural variations in the lithosphere. In one experiment, an upwelling plume is deflected by the keel of a small cratonic block (Central East African Rift and Tanzanian/Victoria craton) and is preferentially channeled along one of the craton sides, leading to the coeval development of a magma- rich and a magma-poor rift along the opposite sides of the craton. The cratonic block also undergoes rotation between the two rift branches, feed by melt from a single mantle source, exhibiting strong similarities with the evolution of the CEAR and the geodetically observed rotation of the Victoria microplate. Our results thus suggest a dominant role for rheology, structure and intra-plate stresses in controlling dynamic topography, mantle- lithosphere interactions, and continental break-up processes above mantle plumes while also reconciling the passive (plume- activated) versus active (far-field tectonic stresses) rift concepts.

Hosted by Brian Evans



A reception in Building 54, Room 923 precedes the talk.

All are welcome.

If you have any questions regarding the lecture, please contact Jen Fentress at 617.253.2127 or jfen@mit.edu. Reservations not required.

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