A structural geology enigma – how do kink-bands form?
Supervision: Dr J-P Latham, Professor John Cosgrove, Dr Jiansheng Xiang
Background
Kink band and box fold geometries are widely observed in multilayered systems at practically all scales of
crustal deformation yet it is clear from physical analogue experiments and many postulated theories that the
possible mechanisms involve a complex mix of phenomena and material behaviours. Layer-bending and
straightening, hinge migration, localised yield, interlayer slip, anisotropy-enhanced rotational instability are
just a few components that have been suggested by eminent structural geologists.
Up until recently, computer simulation tools have been inadequate to represent all the various component
processes that we suspect are important. For example to include: the option of discretely layered components
that move relative to one another while at the same time allowing stresses to transmit across their frictional or
low shear strength contacts; large finite and heterogeneous strain patterns that develop within folded layers;
localised failure within highly stressed bent layers; is a lot to ask from one computational tool. The power of
the FEMDEM method is that it combines the finite element method, FEM (for the internal deformation) with
the discrete element method, DEM (for the discrete interactions between sliding layers). The internal
deformation can be modelled as a combination of elastic viscous or plastic constitutive behaviour including the
possibility of brittle fracture. The VGeST.net workbench has both 2D and 3D FEMDEM solvers implemented in
a modelling environment with pre- and post- processor tools and examples. The breakage model currently
employed in the 2D and 3D FEMDEM solvers allow for tensile and shear failure. This makes the prospect of
combining large finite strains, interlayer-slip, resistance to bending, and local yielding in a multi-layer model all
the more intriguing. In fact, not only have previous numerical models failed to generate the versatile range of
material properties and processes thought to be important in these geological structures, but the setting up of
experiments to investigate these structures in the laboratory has also proven very difficult.
The aim of the project is therefore to explore the evidence for the different mechanisms of formation of kinkbands found in nature using the FEMDEM codes available in VGeST. Field examples will provide the inspiration
for structures at varying scales.
We are looking for an earth science, mathematics, physics or engineering graduate with a strong interest in
structural geology and tectonics. Some computational modelling and code development experience mould be
an advantage but is not essential. Enthusiasm for performing numerical i.e. virtual experiments and linking
results with experimental and field observations is essential. The student will be joining a strong geomechanics
group underpinned by our applied computational modelling group (AMCG), with many applications in earth
science, ocean and industrial modelling. The student will be given appropriate training in the necessary
methods of numerical modelling.
For more information please contact John-Paul Latham (j.p.latham@imperial.ac.uk). For application details
please contact Samantha Symmonds (E-mail: sam.symmonds@imperial.ac.uk, Tel: +44 (0) 207 594 7339).
http://www3.imperial.ac.uk/earthscienceandengineering/courses/phdopportunities/phdapplicationprocedure