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MODEL Report Summary

Project ID: 258830
Funded under: FP7-IDEAS-ERC
Country: Germany

Final Report Summary - MODEL (Mechanics Of Deformation of the Earth's Lithosphere.)

The deformation of lithospheric plates results in a wide variety of geodynamical processes such as subduction of oceanic plates, mountain belt formation, and earthquakes. The result of these processes can be studied by geophysical methods, which give us a glance of the structure of the present-day lithosphere, as well as with a variety of geological techniques which can be used to reconstruct how such processes evolved over millions of years. Yet, the data is incomplete and since most lithospheric processes occur over long timescales and the material properties (rheology) of rocks on such timescales is uncertain, our understanding of the physics of the lithosphere remains incomplete. Here, we developed new numerical models and used them to simulate geological processes in the computer. We compared the computer simulations with available geophysical data, and with geological constraints to better understand the mechanics of lithospheric deformation.
To achieve this, we have developed new parallel software tools to simulate geological processes on a million-year timescale in both 2D and 3D, while taking the nonlinear, temperature-dependent visco-elasto-plastic rheology of rocks into account. We also developed new tools to facilitate creating complex 3D geological input models, as well as a massively parallel inversion framework to couple the models with geophysical data.
Using this, we:
1) Developed the geodynamic inverse modelling approach, which is a new method to constrain the rheology and dynamics of the lithosphere by linking dynamic models of the present-day crust and lithosphere with geophysical observations. The effective viscosity of the lithosphere is one of the most uncertain parameters in geodynamics, because it is derived from laboratory experiments on small rock samples that have to be extrapolated to geological conditions over 10 orders of magnitude in strain rate. Using our method, we can determine the effective viscosity of the lithosphere and their uncertainty bounds in a more direct manner and at the correct length and timescales. An application to the India-Asia collision zone shows that there is not a single unique model that fits topographic, GPS and gravity data, but that instead several (~6) endmember models fit the data nearly equally well. Each of those have a peculiar viscosity and stress-structure of the Asian lithosphere, suggesting which regions would be most beneficial to target with future geophysical campaigns.
2) Obtained insights in the dynamics of subduction and continental collision and the role that lithospheric rheology plays in creating continental plateaus such as the Tibetan plateau. The models highlight the underlying physics of plateau formation and why the Himalaya has a high plateau, whereas the Alps do not have one. Models were also used to address the physics of other lithospheric scale processes, such as the formation of large-scale fault zones, potential subduction initiation mechanisms on Earth and why the early Earth was dynamically quite different from the present-day Earth.
3) Applied models to better understand the physics of crustal scale processes, such as the formation of fold-and-thrust belts (why are some mountain belts fold-, but others thrust-dominated?). An interesting area are the Zagros mountains as the folds there have a rather consistent wavelength. We could demonstrate that this wavelength can be used to extract the rheology of the crust on geological timescales, and developed a method that can simultaneously explain why the Zagros is a fold-dominated area. 3D models of folding showed that the obtained patterns and fold-linkage structures are consistent with observations. Erosional processes and salt diapirs speed up the folding processes but do not affect their spacing. We also addressed the physics and pattern formation in salt tectonics, which is relevant for the hydrocarbon industry.
The outcome of this project thus yielded new tools and methodologies to constrain the rheology of the lithosphere from geophysical data, and gave insights in the physics of some key geological processes on both crustal and lithospheric scale. In many cases, we did not only present numerical simulations, but were able to demonstrate why the models do what they do with a combination of 2D/3D numerical simulations, dimensional analysis and semi-analytical methods. Our capabilities to simulate 3D geological processes have significantly evolved as a result of this project, to a stage where the tools can now be employed on a routine basis to address fundamental geoscientific questions. Yet, at the same time, the methods can also be applied to address topics that are relevant for industry, such as better predicting and understanding the stress state in sedimentary basins, which might reduce drilling risks.

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