Structural Evolution of Fold-Thrust Structures in Analog Models Deformed in a Large Geotechnical Centrifuge

Todd E. Noble and John M. Dixon
Queen's University, Kingston, ON

We investigate the structural evolution of fold-thrust systems by analog scale modelling carried out in a large geotechnical centrifuge at C-CORE, St. Johns, NF. One-metre-long multilayered models of foreland stratigraphic sequences are constructed of plasticine and silicone putty and shortened horizontally at 160 g to simulate the nucleation and progressive growth of fold-thrust structures and fold-thrust systems as a whole.

Plane-layered models composed of five internally laminated stratigraphic units of alternating bulk competency develop geologically realistic duplex structures. An evolutionary relationship between folding and faulting exists: low-amplitude buckle-folds in the competent units localize and control the spacing of thrust ramps in duplex structures. Internal laminations in the competent units reveal the spatial and temporal interplay of faulting, folding and internal strain accrued during development of individual fault-propagation folds. The model fault-propagation folds that develop from plane layers share several characteristics with schematic, geometric and kinematic models of natural fault-propagation folds, e.g., fold geometry (including the amount of thinning of the forelimb), and folding and faulting relationships during fault-propagation folding. In addition, the internal strain accommodation mechanisms active in the model overthrust structures are similar to those documented in natural structures. Contraction faulting, layer-parallel shortening, and rotation of fault-bounded blocks within the competent units facilitate the development of the individual fold-thrust structures. Contour plots of bedding-contraction fault intersection angles reveal the timing when, and the locations on the structures where, the different deformation mechanisms are active.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005